Sustainability & Economical Evaluation of the Smart and Energy Efficient Technologies for the Rammed-earth House in Accra Ghana

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Master Thesis

Sustainability & Economical Evaluation of the Smart and Energy Efficient Technologies for

the Rammed-earth House in Accra Ghana

(Case Study in Accra, Ghana)

Aslan Soltaninazarlou

Tanawut Taechakraichana

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2 Master of Science Thesis EGI_2016-099 MSC

Sustainability & Economical Evaluation of the Smart and Energy Efficient Technologies for the Rammed-earth House in Accra Ghana

Aslan Soltaninazarlou Tanawut Taechakraichana

Approved Examiner

Jaime Arias Hurtado

Supervisor Peter Hill

Commissioner Contact person

Abstract

The energy consumption of buildings contributes 18% of world greenhouse gas emissions (GHG). This fact, along with the current increase in new African buildings, leads to vast opportunities for building sustainable buildings in Africa. The research aims to find which smart and sustainable technologies are economical and suitable for the rammed-earth building project in hot and humid climate for sustainable development, as is the case in Accra Ghana. Two evaluation steps were conducted - technologies evaluation and scenarios evaluation - by simulating energy demand reduction compared to the baseline for economic evaluation in IDA Indoor Climate Energy (ICE) software, together with Microsoft Excel and market research. Ten technologies were initially chosen and applied to the five scenarios by consideration for economics and suitability. The result shows that four out of five scenarios were economical. However, only two scenarios were suggested for the project - Realistic with variable refrigerant flow air-conditioning (Realistic with VRF AC) and Economic Internet of Things (Economic IoT) - when net present value (NPV), payback period, benefit per cost ratio (B/C), and suitability are taken into account.

Moreover, the sensitivity analysis demonstrates that the occupancy pattern affects the energy consumption to some extent, and infiltration rate relates to energy consumption. These methods can be applied for possible future projects, and the results can be used as a reference for projects in hot and humid climates with rammed- earth construction.

Sammanfattning

Energiförbrukningen i byggnader bidrar 18% av världens utsläpp av växthusgaser (GHG). Detta faktum, tillsammans med den nuvarande ökningen av nya afrikanska byggnader, leder till stora möjligheter att bygga hållbara byggnader i Afrika. Forskningen syftar till att ta reda på vilka smart och hållbar teknik är ekonomiskt och lämpar sig för rammade jorden byggprojekt i varmt och fuktigt klimat för hållbar utveckling, vilket är fallet i Accra i Ghana. Två steg utvärderingsfördes - teknik utvärdering och scenarier utvärdering - genom att simulera minskad energiförbrukning efterfrågan jämfört med baslinjen för ekonomisk utvärdering i IDA Indoor Climate Energy (ICE) programvara, tillsammans med Microsoft Excel och marknadsundersökningar. Tio tekniker initialt valt och tillämpas på de fem scenarier av hänsyn till ekonomi och lämplighet. Resultatet visar att fyra av fem scenarier var ekonomiskt. Emellertid var endast två scenarier som föreslås för projektet - realistisk med variabelt

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3 köldmedium luftkonditionering (realistisk med VRF AC) och ekonomiska sakernas Internet (Economic IoT) - när nuvärdet (NPV), återbetalningstid , nytta per kostnadskvot (B/C), och lämplighet beaktas. Dessutom känslighetsanalysen visar att beläggningen mönstret påverkar energiförbrukningen i viss mån, och infiltration avser energiförbrukning. Dessa metoder kan användas för eventuella framtida projekt, och resultaten kan användas som en referens för projekt i varma och fuktiga klimat med rammade-jord konstruktion.

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Acknowledgement

First of all, we would like to express our utmost gratitude to Jaime Arias Hurtado - our examiner - and Peter Hill - our supervisor - for supervising us and giving us exceedingly precious suggestions. Secondly, I would like to thank the CEO of Asaduru company, Mohamed Bedri and the team that gave us the opportunities to work with them and provided this interesting project. Also, we would like to give special acknowledgement to the former architecture of Asaduru, Samer Quintana who provided us with the house design and crucial information.

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List of Figures

Figure 1 shows the flowchart of the experiment processes ... 12

Figure 2 shows the surface temperature of different roof material versus albedo or solar reflectance [30]... 14

Figure 3 demonstrate the spectral characteristics of building materials and also albedo (solar reflectance) and surface temperature for different roof materials [30] ... 15

Figure 4 shows windows R values versus energy consumption rate in cold climates [40]... 17

Figure 5 shows Various windows with different R values versus heating and cooling energy use in cold climates [40] ... 17

Figure 6 shows windows R values versus energy consumption rate in hot and humid areas [40] ... 18

Figure 7 shows Various windows with different R values versus heating and cooling energy use in hot and humid climates [40] ... 18

Figure 8 shows relationship between PPD and PMV [48] ... 20

Figure 9 shows Summer and winter comfort zones in ASHRAE standard [48] ... 21

Figure 10 shows Heat pump/air conditioner sale in Sweden between 1982 to 2014 [56] ... 23

Figure 11 shows the main parts and schematic of the air to air conditioner system [55] ... 24

Figure 12 shows heat recovery VRF system [58] ... 25

Figure 13 shows standard mini VRF system [58] ... 26

Figure 20 shows multi joint cooling system [61] ... 26

Figure 15 shows two pipe fan coil unit system [62] ... 27

Figure 16 four pipes fan coil unit system [62] ... 28

Figure 17 shows different indoor fan coil unit configurations [63] ... 28

Figure 18 shows radiant ceiling cooling panel and its infrared image [65] ... 29

Figure 19 shows temperature variation on surface of a standard cooling panel [65] ... 30

Figure 20 shows AHU and PV systems working together in a hot and humid are [68] ... 31

Figure 21 shows relationship between different dew points, temperature and relative humidity at 1 bar atmospheric pressure [72] ... 32

Figure 22 shows an heat/cool recovery air-handling unit system [71] ... 33

Figure 23 shows the overview of a FTX system [70] ... 33

Figure 24 shows the smart home concept applied to the project ... 34

Figure 25 shows the example of connected light bulb [77]... 35

Figure 26 shows wall and roof occupancy sensor [78] ... 36

Figure 27 shows the concept of tubular light [90] ... 38

Figure 28 shows the concept of designing light shelve [91] ... 39

Figure 29 shows the Nest smart thermostat [94] ... 41

Figure 30 shows the Tado smart air conditioner control [100] ... 41

Figure 31 shows an exterior venetian blind [102] ... 42

Figure 32 shows a window awning [102] ... 42

Figure 33 shows a multi-purpose sensor [109] ... 44

Figure 34 shows the location of the project [18] ... 46

Figure 35 shows the overview of the project [19] ... 47

Figure 36 shows the 3D house model of 3 bedroom plan [19] ... 47

Figure 37 shows the plan for the 3 bedrooms model house of Asaduru company [19] ... 48

Figure 38 an example of Rammed earth construction [21] ... 49

Figure 39 the process of compressing earth in rammed earth construction method [22] ... 49

Figure 40 shows the average temperature and precipitation of Accra Ghana [117] ... 50

Figure 41 shows the seasonal temperature range of Accra Ghana[117] ... 50

Figure 42 shows the wind speed of Accra Ghana [117] ... 51

Figure 43 shows relative humidity in Accra Ghana [118] ... 51

Figure 44 shows the dew point of Accra Ghana [118] ... 52

Figure 45 shows the solar irradiation on the project [19] ... 52

Figure 46 shows the overview of Kyoto Pyramid [23] ... 53

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Figure 47 shows the 3D energy model of 3 bedroom house imported to IDA-ICE [19] ... 55

Figure 48 shows the cooling set point in living room for one day ... 60

Figure 49 shows the temperature set points used in the technologies evaluation for fan coil system ... 62

Figure 50 shows the total energy consumption of the technologies ... 66

Figure 51 shows the energy reduction of the technologies ... 67

Figure 52 shows the incremental investment cost of technologies ... 67

Figure 53 shows the net present value of the technologies ... 68

Figure 54 shows the payback period of the technologies ... 68

Figure 55 shows the benefit to cost ratio of the technologies ... 69

Figure 56 shows the energy reduction of the scenarios ... 70

Figure 57 shows the incremental investment cost of the scenarios ... 70

Figure 58 shows the net present value of the scenarios ... 71

Figure 59 shows the payback period of the scenarios ... 71

Figure 60 shows the benefit per cost ratio of the scenarios ... 72

Figure 61 shows the CO2 reduction from the scenarios ... 72

Figure 62 shows the effect of type of occupancy schedule on energy consumption ... 73

Figure 63 shows the effect of variable fixed ACH on the energy consumption in comparison with baseline ... 74

Figure 64 shows the effect of variable fixed ACH on CO2 level ... 74

Figure 65 shows the effect of variable fixed ACH50 on the energy consumption ... 75

Figure 66 shows the effect of variable ACH50 on CO2 level ... 75

List of Tables

Table 1 shows the zones geometry ... 56

Table 2 shows the rammed-earth properties ... 56

Table 3 shows U-value and thickness of building envelop ... 57

Table 4 shows the glazing properties ... 57

Table 5 shows the windows size and quantity ... 57

Table 6 shows the zones area and number of light bulbs ... 58

Table 7 shows the cooling capacity in the baseline ... 58

Table 8 shows the properties of exterior Venetian blind ... 61

Table 9 shows the designed cooling power for different zones of the three-bedroom house for fan coil system ... 62

Table 10 shows the maximum designed cooling power (W) and chilled water mass flow rates (kg/s) in the different zones of three-bedroom house using cooling panels ... 63

Table 11 shows the financial parameters ... 64

Table 12 shows the initial and changing rate of discounted rate and electricity price in Ghana ... 64

Table 13 shows the range and median of equipment price ... 64

Table 14 shows the technologies applied to scenarios ... 65

Table 15 shows the factors and factors range ... 73

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Nomenclature

Abbreviation

AC Air Conditioning

ACH Air Change rate

AHU Air Handling Unit

BIM Building Information Modelling

B/C Benefit per Cost Ratio

COP Coefficient of Performance

COP2 Cooling Coefficient of Performance

CO2 Carbon Dioxide

FTX Från och Tillluft Värmeväxling-Supply and Exhaust Air Heat Exchanger

GHG Greenhouse Gas

GWP Global Warming Potential

HVAC Heating, Ventilation and Air-conditioning

ICT Information and Communication Technology

ICE Indoor Climate and Energy

IOT Internet of Things

LED Light Emitting Diode

PIR Passive Infrared

PVent Personal Ventilation

PV Photovoltaic

PPD Predicted Percentage of Dissatisfied index

PMV Predicted Mean Vote index

RFID Radio Frequency Identification SEMS Energy Management Systems

UN United Nation

U value Rate of transfer of heat through a structure divided by the difference in temperature across that structure

VRF Variable Refrigerant Flow

WWR Windows to Wall area

Symbol

Al Area of Utilization [m2]

C Corrected Cooling Consumption [kWh/year]

Cu Coefficient of Utilization

Fc Lighting Cooling Factor [kWh/year]

F Future Value [USD]

I Lighting Output [lux]

i Interest Rate [%]

L Lighting Energy Reduction [kWh/year]

Li Total illumination [lux]

LLF Lighting Loss Factor

n Considered Period [Year]

P Present Value [USD]

Pa Pressure [Pascal]

S Simulated Cooling Consumption [kWh/year]

T Total Cooling Consumption [kWh/year]

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Project description

Awareness of global warming has become increasingly important in this era. Greenhouse gases (GHG) emissions, a major influence on global warming, are mainly emitted from energy consumption of the residential sector, which is 18% of the world GHG, 21% in the United States[1] and 23% in Australia [2] . Globally, the urban population will increase to five billion or 60% of the world population by 2050 [3], and will lead to an increase of energy consumption in the residential area, especially, in developing countries in Asia and Africa continents.

Because of these reasons, developing countries in the region need to be sustainably planned. The population in Africa is counted to be around 1.2 billion, which was projected to reach 2.5 and 4.4 billion in 2050 and 2100 respectively [4]. Currently, 60% of the African population does not have access to energy with annual 7 % increase of urban energy demand. The United Nations (UN) set up the global challenge by guaranteeing that the world can have access to modern energy by 2030, and will increase energy efficiency and renewable utilization by double [5]. Moreover, buildings' energy consumption is considered as 56% of the total African energy consumption which is 75% of the electricity generation [5]. The rapid increase in energy demand causes an energy deficit in the region. However, the forecast by [5] reveals the potential of improving building energy consumption since about 75% of the buildings will be newly built according to the forecast. Therefore, the supply of future energy consumption needs to be thought carefully in the most effective way. These issues can be tackled by applying current and future technologies such as using heat pumps, sustainable and energy efficient house design and an integration of information and communication technologies (ICT). However, the main factor that a house owner and engineers need to consider before implementation is the economic feasibility. However, there is no clear picture of the overall technologies of smart and sustainable and energy-efficient house both individually and wholly as a system. End users and engineers find it difficult to decide which technologies are economical and worthy to invest in, particularly for a future project.

Asaduru is a Swedish company focusing on sustainable development with expertise in rammed earth construction, which gives more advantages than the traditional way of construction using concrete. Rammed- earth is an environmental friendly construction method from cradle to grave since it uses mostly local materials like soil, sand and sometime stabilizer like cement. In addition, it has a good thermal mass capacity with an average U-value (average heat transfer coefficient like concrete) without insulation layer in between. The company pursues to develop a project as a model for sustainable houses in Ghana, Africa. The company aims to develop 20 houses to supply the upper-middle class in Ghana with a sustainable community prototype, and plans to develop a project for the low-middle class in the future since Africa lacks several million households.

The project will combine sustainable construction, sustainable house and smart home concepts to develop the most efficient and affordable house model focused on self-sufficient communities and zero/low GHG emission.

The similar energy efficient house projects conducted in hot dry and hot humid climates shows that the interior temperature in the houses can be reduced by the utilization of various passive techniques like window shading, natural ventilation, choosing convenient orientation, thermal energy storage systems, evaporative cooling, night ventilation, night sky radiation cooling and thermal inertia. All of these techniques result in increased comfort inside the houses [6], [7]. In the same way as, the internet of things is used to control alongside with an efficient and economical cooling system and ventilation for achieving the lowest energy demand as possible for implementation in rammed-earth house, which is already well-known for using a sustainable material.

This research will be prepared for Asaduru under Royal Institute of Technology's supervision, which aims to evaluate the breakeven point of different technologies in the market to combine as scenarios for simulating the energy reduction of technologies and scenarios compared to the baseline. These studied technologies will be considered for the project plan before construction.

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Objectives

The main objective of this thesis is to consider the appropriate systems to be applied to the rammed-earth houses project in Accra, Ghana from a techno-economic point of view. To achieve the objective, some sub- objectives need to be done as follows.

- Study the main principle of the technologies for applying to the building at Asaduru sustainable house project.

- Develop different scenarios to evaluate the most appropriate technologies for the sustainable buildings.

- Evaluate energy performance for different scenarios in order to assess the energy reduction, costs and environmental impact.

Method and Approach

The literature reviews of Accra's climate condition, smart and sustainable technologies, rammed-earth construction and market research of the technologies were investigated. The house model was provided by Asaduru. The energy simulation using IDA-ICE version 4.7 with student license is followed by an economic evaluation of technologies and scenarios as a system using Microsoft Excel financial functions, along with market research and basic assumptions. The IDA-ICE makes use of the best and latest building energy model available along with variable time step instead of "hand code component subroutines" [8]. Furthermore, the software is capable of adapting the controlled strategy, which enables the users to apply basic control principles. The IDA- ICE is believed to be a suitable software for both non-existing and existing projects for energy demand simulation by applying different technologies and controlled strategies. The building information and basis of smart device principles applied to the simulation were obtained from literature review. The weather data were taken from Energy Plus website, which conducts real measurement of weather in a number of different countries. The latest weather file in March 2016 was used in the simulation.

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Overview

FIGURE 1 SHOWS THE FLOWCHART OF THE EXPERIMENT PROCESSES

The processes of the experiment are shown in Figure 1. The process starts with data collection to obtain the available technologies in the market for applying in the simulation software IDA Indoor Climate and Energy (ICE).

The energy simulation, economical evaluation and suitability were conducted to initially obtain an idea of which technologies will be put into the different scenarios. After the selection of the technologies in to three scenarios- Realistic, Highest Energy Reduction and Economic, energy simulation and economical evaluation, again, will be conducted to be able to decide that which technologies best match to the projects.

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Literature review

The first step of methodology is to review different technologies, which would be applied in the project. Different passive-energy efficient and smart systems will be discussed and reviewed for their principles, price and the products available in the market. Not all of them may be implemented in this project, but can be a good guideline to the future works in this field. Moreover, some previous similar projects will also be evaluated.

Previous work

A research by Torunski et al. [9] discusses the potential of energy saving when smart systems are applied. Four methods were compared, from which three of them are actual measurements. Only one simulation method, which is done by University of Karlskrona, was stated in the paper. A research by Hussain et al. [10] displays the potential of home automation on energy saving by measuring energy consumption in four houses before and after the installation. It found out that home automation could decrease energy consumption by 18.7%;

however, the site location, weather and house material were not defined. Several years later, the Energy Management System (SEMS) was purposed by Park et al. [11] who experimented on a system that consists of sensors, a home management system and three appliances using wireless communication. Some research examines single smart devices; for example, a lighting schedule using “life log data” was investigated in Yang et al. [12] for evaluating lighting energy consumption in smart houses. There are many types of simulation software used for energy consumption simulation. In 2015, there was a research by Shoubi et al. [13] that tried to reduce energy demand by applying the simulation software. The study aims to find an alternative material for reducing a building's energy demand using Building Information Modelling (BIM). A double floors house in Johor, Malaysia was a case study that suggested an alternative design for the project. Another research by Mehdiand et al. [14]

investigated and optimized electricity consumption for appliances, which were differentiated into four types of appliances, using mathematical models. One interesting and well-known simulation software is IDA Indoor Climate and Energy (IDA-ICE). The software is appropriate for incorporating HVAC and lighting systems with a controlled strategy of the technologies. One research by Hilliaho et al. [15] investigated the appropriateness for IDA-ICE to simulate energy consumption of glazed space compared to the actual measurements. Recently, a research applied IDA-ICE to investigate the effects of the traditional assumption on the returned temperature of the heating system [16]. The result shows a good approximation. Moreover, research by Taylor et al. [17]

shows the energy consumption of rammed-earth offices compared to concrete offices. It said that there is a high possibility for the energy consumption reduction to be well designed and that the control strategy could be changed. However, none of the research were conducted for a future project with rammed earth construction, adapted not only for controlled strategy, but also for cooling demand in a hot and humid climate with the best thermal comfort, and considered all the technologies as a system in regards to economical point of view.

Therefore, the objective of this thesis is in the following section.

Reflective roofs

Unlike the regions located in the northern hemisphere, which normally are in need of both cooling and heating, most of the tropical or subtropical areas such as the location of our project in Accra, mostly are in need of cooling. This is the main concern in construction of the houses in tropical and hot-humid climates [26].

Since the majority of the heat gain which is originated from solar irradiation is coming from windows, roof and walls, passive cooling techniques can be implemented to the envelopes to reduce the cooling demand without compensation with large amounts of valuable energy [27]. Passive cooling techniques are mostly preventive measures against increasing the temperature inside the buildings. According to Asimakopoulos et al. [28], the reflective cooling technique is mainly aimed to slow down the heat transfer into the building. The reflective roof technique which is investigated by Givoni et al. [29] showed a promising effect in terms of reducing heat transfer through the roof to the entire envelope. Also, the color and thermo-physical properties (solar reflectance and

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14 thermal emittance) of the roof material have a huge effect on external surface temperature. Figure 2 and Figure 3 demonstrate the impact of roof material and roof color on albedo or solar reflectance and also on surface temperature. The measurements are conducted in same outdoor condition and it is clear that utilizing light colors like white and grey can maintain the surface temperature at lower rates rather than dark colors like black which has almost 100% hotter surface temperature.

FIGURE 2 SHOWS THE SURFACE TEMPERATURE OF DIFFERENT ROOF MATERIAL VERSUS ALBEDO OR SOLAR REFLECTANCE [30]

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15 FIGURE 3 DEMONSTRATE THE SPECTRAL CHARACTERISTICS OF BUILDING MATERIALS AND ALSO ALBEDO (SOLAR REFLECTANCE) AND SURFACE TEMPERATURE FOR DIFFERENT ROOF MATERIALS [30]

Moreover, Akbari et al. showed that increasing the solar reflectance of the roof material from 0.1 to 0.35 can decrease the cooling demand by approximately 7 % inside the envelope [30]. Still, accumulation of dust and dirt on reflective roofs can reduce the reflectance factor and increase the maintenance. Visual discomfort is another aspect to take into consideration for reflective roofs.

However, nearly all the researches that were implemented to find out the effect of the reflective roofs are from countries with hot and dry climate. Thus, more investigations must be done in hot and humid regions like Accra, Ghana to understand the effect of cool roofs [26], [31] .

Finally, according to Stetiue et al., reflective and radiative cool roof techniques are among the most effective and cost competitive measures in terms of cooling energy reduction methods. This positive contribution can reach to 42% in hot arid areas and to 17 % in humid regions [32].

Green roofs

One of the well-consolidated methods to reduce the cooling demand inside the buildings is the green roof technique. This technology is able to not only generate considerable energy savings but also improve the thermal performances of the building and provide other ecological benefits [33], [34].

While according to Bevilacqua et al. [34] green roof technique can decrease the surface temperature of the roof by 12C in the hot and arid climate of Southern Italy-Calabria, it only can decrease the roof surface temperature in a hot and humid region like Hong Kong by 5.2C [35].

This research clearly shows the difference between the green roof effect in hot and humid versus hot and dry climates. Obviously, the effect of the green roof on cooling energy reduction is much higher for hot and dry climates in comparison to hot and humid ones. This crucial factor should be taken into account when the green roof technique is going to be implemented in the project in Accra , Ghana with high humidity all over the year.

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16 Moreover, Jim et al. demonstrated that the cooling effect of the green roof is diminishing on rainy and cloudy days in contrast with sunny days [35].

Beside all above, according to Lamnatou et al. [33]. the combination of Photovoltaic panels (PVs) with green roofs technique which can be a novel method in the construction sector, may provide advantages like an increase in PV output due to interaction between PV and plantation. This is mainly due to slightly lower temperatures under or around PV panels, which play a crucial role to increase the PV panel efficiency especially in hot seasons.

Natural ventilation

The two main natural ventilation systems can be named as wind catchers and cross ventilation. However, according to some surveys higher relative humidity has a negative effect on cooling energy demand reduction in hot and humid areas. Zhang et al. [36] clearly demonstrated that at the outdoor temperatures of over 28 °C and relative humidity above 70%, the indoor temperature of the building will rise by 0.4 °C for every 10% increase of relative humidity. While the average relative humidity level in Accra is around 76 to 86% around the year and wind velocity is not so high either, utilizing the natural ventilation methods to decrease the cooling demand is not seemingly useful. In the other words, opening the windows and doors to allow the outdoor fresh air to infiltrate the indoor area will directly affect the cooling demand negatively in almost all months in Accra [7], [37].

Another research which is done by Aflaki et al. [38] demonstrated that high humidity levels, persistent cloud cover and low temperature differences between day and night are among the main constraints against the use of natural ventilation as a prevalent strategy in hot and humid climates. The maximum effect of natural ventilation can be achieved when it relies on some strategies to avoid heat gain in envelopes. In other words, limiting the solar absorption of the house, window to wall and window to floor ratio measures, house orientation and design are the main factors which should be taken into consideration in projects that will be constructed in hot and humid areas [38].

Insulation and windows

One of the important strategies for building energy conservation is insulation of the building envelope for both opaque and transparent structures. By this, insulation of the different parts of the house such as roofs, walls, floor and even foundation can be defined as essential factors of an energy efficient house. Furthermore, having better insulation in transparent areas like windows and skylights can reduce the heating and cooling energy loss in the buildings. Also, it is documented that the thickness of the insulation layers has a big impact on savings which are achieved by reduction in energy use. According to Karlsson et al. [39], it is still uncertain how much insulation is the optimum for reducing the energy consumption in a single family house. Nevertheless, most of the surveys showed that insulation has a minor role in hot climates regarding saving cooling energy inside the house. In other words, the benefit of insulation in hot and humid climate is too low in comparison to cold climates [40], [41].

Also, the heat gain in hot and humid areas are mainly coming from solar radiation and conduction through windows, infiltration and conduction through walls and roof. While these are referring to outdoor condition and temperature, internal heat gains from electrical appliances, occupants and lighting stand for about one third of the total heat gain in a single family house.

Something which is worth to know about wall and roof insulation strategies in hot and humid areas is that the insulation does not have a significant role regarding cooling demand reduction in the building. Kim et al.[40]

clearly showed that decreasing the U value of the wall insulation in a hot and humid area like Florida in the US will just decrease the home energy consumption slightly. This is almost the same for roof insulation strategies [42]. In overall, adding insulation layers to the building envelope in hot and humid climates will insignificantly change the cooling demand.

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17 To our knowledge the effect of windows glazing and insulation is much better for cold climates rather than hot climates. Kim et al. [40] showed that in cold climates, triple glazing window with a U value of 1.65 W/m²K consumes 50% and 18% less energy in comparison with single glazed window with a U value of 5.68 W/m²K and double glazed window with a U value of 2.84 W/m²K, respectively. In other words, in cold climates, increasing the insulation layers and air/gas gaps between window glazing directly affect the energy consumption inside the buildings. Nevertheless, the positive effect of the increased glazing is mostly seen for heating demand and it can reduce the heating energy and not cooling demand. Figure 4 and Figure 5 demonstrate the energy consumption rate against windows R-values (R-value=1/U-value) and heating/cooling energy consumption for various windows R-values, respectively, in cold climates.

FIGURE 4 SHOWS WINDOWS R VALUES VERSUS ENERGY CONSUMPTION RATE IN COLD CLIMATES [40]

FIGURE 5 SHOWS VARIOUS WINDOWS WITH DIFFERENT R VALUES VERSUS HEATING AND COOLING ENERGY USE IN COLD CLIMATES [40]

On the other hand, when increasing the windows insulation and glazing in hot and humid areas are discussed, it came up with an interesting result. Windows with U value of 5.68 W/m²K and 0.57 W/m²K have nearly identical heating and cooling energy consumptions [40]. It means that utilizing single/double glazed windows in hot and humid regions like Accra is more appropriate regarding energy savings and economical aspects.

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18 Eventually, the negligible role of better insulation in walls, roof and windows in hot and humid areas is mainly due to the small temperature difference between indoor and outdoor temperatures. Figure 6 and Figure 7 show the correlation between various windows with different R values with heating and cooling energy use in hot and humid areas of the US.

FIGURE 6 SHOWS WINDOWS R VALUES VERSUS ENERGY CONSUMPTION RATE IN HOT AND HUMID AREAS [40]

FIGURE 7 SHOWS VARIOUS WINDOWS WITH DIFFERENT R VALUES VERSUS HEATING AND COOLING ENERGY USE IN HOT AND HUMID CLIMATES [40]

Orientation of the house

It is widely known that house orientation is among the crucial factors which can affect the energy consumption in buildings, positively or negatively, depending on the house location and solar orientation [43], [44]. While in cold climates, facing the buildings toward more solar radiation is more desirable, in hot climates this should be reversed where solar radiation should be avoided to leak through the envelope. According to surveys done by some passive house research groups, an energy saving of 20 to 36% can be achieved if correct landscape, location and orientation is chosen for the buildings [45].

The house orientations which face South and Southeast have the benefits of free solar gains and free lighting during some hours a day for areas located in northern hemisphere. This is because that sun is shining from

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19 Southeast to Southwest with a slight angle during a whole year in northern hemisphere. Conversely, sun shines from Northeast to Northwest in southern hemisphere [46]. Although, depending the construction company's desire and customers request the orientation, shape and plan of the houses can be changed regardless of their role on energy consumption of the building.

Indoor climate and thermal comfort

According to ASHRAE, thermal comfort can be defined as “the condition of mind that expresses satisfaction with the thermal environment”. The judgment of thermal comfort depends on many inputs influenced by physical, physiological, psychological, and other processes affected by occupants [47].

Humans have a very effective, complex and not fully understood unconscious temperature regulatory system.

This system is working to hold the body core temperature at 37°C according to metabolism, respiration, blood circulation near the skin surface and sweating. Obviously, there are some environmental factors which affect the sense of thermal comfort in humans that are; temperature, air velocity, humidity and radiation. In addition, the upper limit for the wet bulb temperature or severe heat stress for both unclothed and clothed individuals is around 30°C at air speeds of 0.1 to 0.5 m/s [47]. On the other hand, acquiring the correct and desirable indoor temperature and relative humidity level implementation of mechanical or passive cooling systems like AHU or AC is necessary. These systems will be explained in detail in the next parts of the report.

Beside all above, to get an optimum indoor air quality (IAQ) in buildings, ventilation systems and air infiltration play a crucial role. By this, occupants can achieve; a better thermal regulation, in and outdoor pollution control and desirable fresh air [47].

PPD and PMV and Comfort Zones

Getting back to the basic definition of the thermal comfort for occupants we can define the Predicted Percentage of Dissatisfied index (PPD) and Predicted Mean Vote index (PMV) values. These values, which are defined by Fanger (Fanger 1970) can be used " to predict mean value of subjective rating of a group of people in a given environment". This is mainly due to variation of the thermal comfort sense for different individuals. According to Fanger, PMV values between +1 and –1 are acceptable, while values higher than +1 or lower than –1 are not desirable and are counted as dissatisfaction limits. The formula for PMV is shown below.

EQUATION 1 FORMULAR FOR PMV

𝑃𝑀𝑉 = (0.303𝑒^−0.036𝑀+ 0.025)𝑥[(𝑀 − 𝑊) − 𝐻 − 𝐸𝑐− 𝐶𝑟𝑒𝑠− 𝐸𝑟𝑒𝑠] (1) Where

M - metabolic rate, W/m²

W - effective mechanical power, W/m²

H - dry heat loss, heat loss from the body surface through convection, radiation and conduction, W/m²

Ec - evaporative heat exchange at the skin, when the person experiences a sensation of thermal neutrality, W/m²

Cres - respiratory convective heat exchange, W/m² Eres - respiratory evaporative heat exchange, W/m²

Another Fanger value, which is called PPD, can be used to predict the number of individuals who are not satisfied with a given thermal condition. As it is shown in Figure 8, PPD of 10% corresponds to PMV of ±0.5 which is widely accepted as a scale for thermal comfort in the world [47], [48].

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20 FIGURE 8 SHOWS RELATIONSHIP BETWEEN PPD AND PMV[48]

These two values will be used in our project to show the thermal satisfaction for every zone in the house.

Furthermore, in order to understand and achieve the thermal environmental conditions for human occupancy, there is a standard of ASHRAE 55, which expresses the comfort conditions or zones for at least 80% of the sedentary or slightly working occupants who find that zone thermally comfortable and acceptable. This standard scale includes winter and summer seasons with CLO values of 0.9 (0.14 m².K/W) and 0.5 (0.078 m².K/W), respectively. Figure 9 shows the chart for ASHRAE summer and winter comfort zones.

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21 FIGURE 9 SHOWS SUMMER AND WINTER COMFORT ZONES IN ASHRAE STANDARD [48]

Relative Humidity and dew point

Relative humidity or RH can be defined as a "ratio of partial pressure of the water vapor in the air to the pressure of the saturated vapor at the same temperature" [48].

The RH percentage is mainly useful when the dry bulb temperature is known for the specific condition. According to most of the literatures and ASHRAE handbook the standard RH value for indoor condition is around 50% at 21°C. However, in order to avoid condensation on cold surfaces we may need to maintain the RH value lower than 50% depending on the indoor environment conditions. That is why we need to define another variable called the dew point. The dew point is an atmospheric temperature (depending to pressure and humidity) below which water droplets start to condense and dew can form. It is also a tool to measure the humidity of the environment. At the dew point temperature, the saturated water vapor pressure is equal to the ambient vapor pressure. Below the dew point, saturated water vapor will begin to condense on solid surfaces that are colder than dew point temperature. It is worth to know that due to commonly high relative humidity levels in Accra, specific measures and cooling strategies should be considered for the designed houses [47]–[49].

Ventilation rate and CO

2

level

It is documented that in order to acquire optimum air quality and thermal comfort in buildings, utilizing and implementing ventilation are an important role. This is mainly due to the accumulation of undesired pollutants derived from the occupants’ activities inside the building that consequently lead to the need for introducing a reasonable amount of fresh air and removing aged air from the building. In other words, while the building is

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22 being designed, infiltration and ventilation rates should be taken into consideration to get the desired indoor air quality (IAQ). In accordance with ASHRAE Standard 62, the minimum fresh air ventilation per person for any type of building is 8 l/s which is able to dilute the CO2 concentration inside the envelope and maintain it around 700 ppm. This concentration is nearly the same as the typical CO2 generation rate per person inside a closed envelope. Although, CO2 is not counted as a hazardous or toxic gas inside the building, it should be diluted accordingly to achieve a desirable IAQ. Nevertheless, the recommendations for CO2 level in ASHRAE standard 62 for different building types are for classrooms and conference rooms 15 cfm (7 l/s) per occupant. For office space and restaurants 20 cfm (9.5 l/s) per occupant is recommended and for hospitals, it is 25 cfm (12 l/s) per occupant.

[1 cfm (ft³/min) = 1.7 m³/h = 0.47 l/s] [47], [48], [50].

Also, the minimum ventilation rate for a building is 0.35 l/s.m² of living areawith regard to Swedish house regulation standards [51]. This is the minimum amount of outside fresh air ventilation rate if there is occupancy in the room or zone, otherwise, the ventilation rate should be around 0.10 l/s.m² of living area. This clearly shows that even though the building can be unoccupied in some hours of the day, the ventilation system should provide some amount of fresh air to the zones. Furthermore, it is recommended that buildings and envelopes are exposed to forces of ventilation or airing at least once a day [51].

Occupancy factor

Occupancy and rate of the occupancy are among the most effective and crucial factors in building design, operation and maintenance. While occupancy can influence the lighting, ventilation, indoor air quality (IAQ) and temperature, it should be elaborately predicted and surveyed before the house construction phase starts [47].

For instance, overestimating the occupancy rate inside the buildings can lead to oversizing of the mechanical cooling systems and thus over predicting cooling loads. This can also lead to misinterpretation of the building energy performance simulations. Ding et al. [52] documented that with a proper occupancy schedule the cooling demand for the building can be reduced by 36%.

However, interior disturbance arising from occupant behavior is accounted as the main hindrance and uncertainty in order to get an elaborate prediction over occupancy schedule. Another survey that is conducted by Carlucci et al. [53] showed that different occupancy schedules have a statistically significant influence on the building’s energy performance, especially cooling energy demand. However, the effect of occupancy schedule is seen more in high-performance buildings rather than poorly insulated buildings. Thus, despite high costs and modeling time, more detailed and precise description of occupancy and occupant-dependent input variables is required in order to get an accurate energy and performance modeling for a high-performance building [53].

Mechanical Cooling Systems

Unlike passive cooling systems where mechanical parts like pumps, fans or compressors are mainly avoided, active cooling/heating systems have some running parts that allow users to maintain the indoor climate in a desirable and acceptable level. Generally, the heat and cooling transmitting process can be done by means of convective systems like warm air systems and convector systems (heat pump/air conditioning and fan coil), convective and radiative systems like floor heating systems and radiator systems and finally radiative systems like ceiling heating/cooling systems. To our knowledge, convective systems have more priority due to providing more evenly distributed heat/coolness inside the envelope in comparison with radiative systems, which are used mainly to cover local heating/cooling demand. Accordingly, the energy consumption of the former systems is generally more than the latter.

However, the mechanical cooling systems can be divided into three main categories of; all air systems, air and water systems and all water systems [47], [48].

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23

Split type ductless air to air conditioning systems

Generally, the majority of home and small commercial air conditioning systems utilize and circulate refrigerant in a closed “split” system to cool/heat and condition inside air. In case of cooling, outdoor air is the medium used to re-cool and condense the refrigerant. In turn, the cooled refrigerant is pumped to indoor evaporator unit to take the heat from the space and cool down the room [54], [55]. Figure 10 shows the yearly sold air to air heat pump/air conditioner systems in Sweden from 1982 to 2014. Other types of the heat pumps like air to water, air to brine and supply air heat pumps are shown too. Only in 2008, more than 75,000 air to air heat pump/air conditioner have been sold which clearly shows the popularity of this product. Also, there is a lack of statistical information for air to air heat pump selling rate between 2012-2014[56].

FIGURE 10 SHOWS HEAT PUMP/AIR CONDITIONER SALE IN SWEDEN BETWEEN 1982 TO 2014[56]

Compressor is the heart of the system and can be reciprocating, scroll or screw type. There is a four-way valve located at outdoor unit after compressor which switches the cooling and heating direction when it is needed.

The condenser coil is the outside unit in case of cooling. Outdoor and indoor fans pull and blow air from and to the atmosphere, respectively The evaporator coil is the inside unit in case of cooling and other minor parts like water drainage system and filters. Figure 11 shows the main components of a split-type air to air heat pump/air- conditioner.

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24 FIGURE 11 SHOWS THE MAIN PARTS AND SCHEMATIC OF THE AIR TO AIR CONDITIONER SYSTEM [55]

This popular cooling system has some pros and cons, which should be taken into consideration especially in such projects that visual impact of the house auxiliary systems like cooling apparatus is important for clients and construction companies.

Since these systems' hearts are located at outside of the house, operation and maintenance can be carried out easier during lifetime of the system. In other words, piping, compressors, fans, wiring system and noise producing parts are separated from the indoor unit, which in turn may reduce the inconvenience to the occupants. Another advantage is that they are ductless, and the interior unit is completely inside the thermal shell [57]. Moreover, seasonal changes cannot affect the cooling process especially in a hot and humid climate like Accra with an even outdoor temperature around the year. Dehumidifying is among the main advantages of these systems, which enables the end users to feel comfortable in hot and humid climates. Visual impact of the air to air conditioner is not the only drawback of these systems. This can be more complicated if the house owner wishes to install more than one split type AC in his/her house[48], [54].

Variable refrigerant flow (VRF) and multi joint cooling systems

The next generation of the split type air to air conditioning systems can be called variable refrigerant flow or VRF cooling/heating systems, which is used in residential and commercial buildings. This technology has been widely used in Japan formerly, and it has reached the European and American markets in 1987. These systems have been implemented in more than 50% of medium-sized commercial and residential buildings and 33% of large commercial buildings in Japan. Similar to split AC systems, cooling or heating energy is transferred to or from the space directly by circulating refrigerant (different refrigerant types like R410A with inverter technology can

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25 be used) to evaporators or indoor units located near or within the conditioned space. VRF technology is more complex, sophisticated and flexible in comparison with ductless split and ductless multi joint (multi split AC systems) conditioning systems. Also, they have larger capacities starting from 11 kW to 200 kW capacities depending on the cooling/heating requirement of the buildings. Capability of connecting the outdoor unit/units to several indoor (evaporator in cooling case) units with just one main piping line, having multiple compressors and complex oil and refrigerant management and control systems can be considered as the superiorities of these systems when compared to the old and conventional split AC systems.

Considering the VRF term, it is referred to "the ability of the system to control the amount of refrigerant flowing to each of the evaporators, enabling the use of many evaporators of differing capacities and configurations, individualized comfort control, simultaneous heating and cooling in different zones, and heat recovery from one zone to another" [58]. Some advantages of these systems are; lightweight of every modular unit in comparison with chillers and extendibility of the VRF systems to cover large cooling/heating loads of hundreds of kilowatts, and the design flexibility of the VRF system where as one condensing unit (outdoor unit) can be easily connected to up to 20 indoor evaporating units (indoor unit) with different capacities from 1.75 kW up to 14 kW and different configuration like ceiling recessed, wall-mounted, floor console. Also, for buildings and envelopes requiring simultaneous heating and cooling VRF can be a good choice. In contrast with multi split AC systems, while one zone utilizes cooling another zone can take the benefit of heating at the same time. Extra heat exchangers which are located in distribution boxes are utilized to transfer some reject heat from the superheated refrigerant exiting the zone to be cooled to the refrigerant that is going to the zone to be heated [58].

Energy efficiency of the VRF AC systems is generally dependent on various factors like climate, type of project, occupancy regime and comparison method. While some research showed that the cooling energy savings by VRF systems utilizing R410A as refrigerant and inverter technology in relatively temperate Brazilian climate may reach to 30%, others showed a little or no savings compared to the conventional water or air-cooled chillers.

The main factor of savings by VRF systems are due to their high part-load efficiency. Another aspect of the VRF systems can be seen when energy losses are considered in the ducting system. According to ASHRAE Standard around 10% of the energy is getting lost inside the ducts in ducted HVAC systems. VRF systems do not need any kind of duct and utilize the evaporative cooling of refrigerant sent by small pipes directly to the needed zone [59]. Figure 12 and Figure 13 demonstrate heat recovery VRF system and standard VRF system, respectively.

FIGURE 12 SHOWS HEAT RECOVERY VRF SYSTEM [58]

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26 FIGURE 13 SHOWS STANDARD MINI VRF SYSTEM [58]

Multi joint or multi split cooling/heating systems have the same principle of working as one to one split type AC systems. The only difference is that in this technology ‘multiple’ evaporator units can be connected to one external condensing unit. This system can easily replace the ducted cooling systems due to their high costs and aesthetically unacceptable view. Also, multi joint cooling/heating systems are appropriate for small to medium residential and commercial applications. However, in this cooling/ heating technology each evaporator (indoor unit) has its own set of refrigerant pipework connecting it to the condenser (outdoor unit). This technique is seen to be very similar to the VRF system but the main difference is that multi joint systems are unable to provide individual control over different independent thermal zones. Also the user cannot utilize cooling and heating for different zones at the same time. Either cooling or heating should be used in this technology. In our project, which consists of 6 different zones or rooms to be conditioned, multi joint cooling systems can be a good choice in regards with their low visual impact and spatial need. The only issue here seems to be the very long refrigerant piping system that comes from the outdoor unit to every indoor unit and makes the multi joint technology less desirable [60], [61]. Figure 14 shows the multi joint cooling/heating system.

FIGURE 14 SHOWS MULTI JOINT COOLING SYSTEM [61]

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27

Fan coil cooling systems

Fan coil systems, which are categorized under waterborne, hydronic or all water systems, are used in many different type of buildings for several decades worldwide and became a popular cooling, heating and ventilation technology. The basic components of a fan coil unit are heating/cooling coil, fan section, and a filter. The system is flexible enough to work alone in one zone or to be connected by ducting system to serve multiple zones. Fan coil systems can be controlled by a manual switch, thermostat, or more complicated and sophisticated building management systems. It is very interesting to know that Building Control System or Building Energy Management System can easily manage and control the fan coil units regardless of their configuration and size.

Furthermore, the main energy carrier in this technology is water which is heated by a boiler or cooled by a chiller in a central plant and sent to the units inside the house or building. Also, in cold climates in order to prevent freezing of the water some chemical treatment is often involved and conducted in water. This includes the addition of propylene, ethanol or ethylene glycol to water. However, these additives alter the heat transfer properties of the fluid and designers should be aware of this issue before adding them to the system [62], [63].

Fan coils typically utilize a two or four pipes configuration. While two pipe systems cannot use both heating and cooling at the same time for different zones, four pipes systems have the ability to use both cooling and heating simultaneously. Although, two pipe systems have lower initial costs and installation process is easier and less time consumer, they are not flexible with cooling and heating demand since changing from one to another for the entire system is a time-consuming process. In other words, some issues can arise such as when seasonal or occupancy loads change for starters. Obviously, four pipe systems have higher piping and installation costs but occupant comfort and IAQ can be kept at an acceptable level in all seasons and conditions. Figure 15 and Figure 16 show the two and four pipes fan coil configuration in detail [62].

FIGURE 15 SHOWS TWO PIPE FAN COIL UNIT SYSTEM [62]

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28 FIGURE 16 FOUR PIPES FAN COIL UNIT SYSTEM [62]

As it comes from the name of this system, fan coils always have a fan to blow air across a chilled or heated water coil, which in turn is supplied to the zone or room. The supply air can be a mixture of outside and inside air with specific percentage or just a recirculation of the inside air [62], [63].

Another aspect of the fan coil systems is the capability to remove the undesired humidity inside the envelope in hot and humid climates. As the warmer and moist air passes through the cooling coil which has a temperature below the dew point temperature of the ambient air, condensation occurs on the surface of the coil immediately. This can create serious issues with regards to water leakage under or around the indoor units if the unit is not installed correctly. Auxiliary condensed water pipes that lead the condensed water from indoor unit to the outside of the building are very important and must be correctly installed. To our knowledge, while the average relative humidity level in Accra is between 70 to 85% throughout the year, dehumidification measures should be taken into account during the designing of the cooling systems.

Figure 17 demonstrates the various coil unit configurations that can be installed in different places of the building depending on the zone requirements. While some of them can be installed under ceiling (horizontal fan coils), others are directly installed on floor (vertical fan coil units) [63].

FIGURE 17 SHOWS DIFFERENT INDOOR FAN COIL UNIT CONFIGURATIONS [63]

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Radiant Cooling Panels

This technology is very similar to radiant heating systems but in reverse. The thermal energy is exchanged between the cooling panels and heat loads present in the zones or rooms. Even though there is no forced ventilation to facilitate cooling, a uniform cooling gradient in the room can be achieved. Thus the risk of a draft is naturally avoided by means of this technology [64].

It is recognized that the dominant cooling mode of the ceiling radiant cooling panels are long wave radiation heat transfer. Several attempts have been made in order to obtain the indoor non-steady state radiation heat transfer model of radiant ceiling cooling. A paper written by Zhang et al. [36] is a good example of them.

According to Ning et al. [65] radiant cooling panels have the potential of energy savings, good indoor environment provision and improved thermal comfort. They found that radiant cooling panels, which are modified with thin air layer, not only can provide a uniform surface temperature distribution but also may control the condensation issue in hot and humid climates. This is mainly in contrast with finding of other survey conducted by Hu et al. [66] in hot and humid areas of China. They clearly showed that condensation is one of the problems that limits the application of radiant cooling in hot and humid areas. According to Tang et al. [67]

the condensation rate on the radiant ceiling was 25% greater than that on the radiant wall and 3.5 times greater than that on the radiant floor. One of the most effective measures that can be suggested to overcome this crucial issue is by increasing the chilled water temperature to prevent condensation. However, by this, the cooling capacity is decreased with the increase in chilled water temperature which is not desirable and may lead to decreasing thermal comfort and increase the percentage of PPD which is not acceptable. Another solution to the condensation issue is to utilize a parallel installed ventilation or small air handling unit (AHU) which is capable of dehumidifying the entering fresh air and recirculating the room air at the same time. Also, the entering chilled water temperature to the panel is generally between 14 °C and 16 °C. Figure 18 shows the radiant cooling panel and its infrared image.

FIGURE 18 SHOWS RADIANT CEILING COOLING PANEL AND ITS INFRARED IMAGE [65]

As a summary, we add the advantages of the radiative cooling panel systems as below;

It decreases the mechanical cooling load and operational costs while the cooled ceiling panels operate at relatively high temperatures like 16 °C. It also works under silent and draft free conditions in contrast to conventional air conditioning systems like split AC or VRF systems. Finally, it possesses smaller spatial requirements in comparison to ducted HVAC systems. Figure 18 and Figure 19 demonstrates the temperature variation acquired by CFD simulation on a standard cooling panel.

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30 FIGURE 19 SHOWS TEMPERATURE VARIATION ON SURFACE OF A STANDARD COOLING PANEL [65]

Air Handling Units and Ventilation Systems

One of the crucial and essential components when dealing with house design and thermal comfort is ventilation.

As already mentioned before in the thermal comfort part, the need for having ventilation is mainly due to accumulation of undesired pollutants derived from occupants’ activities inside the building which consequently need an introduction of a reasonable amount of fresh air and removal of aged air from the building. While with regards to ASHRAE Standard 62, the minimum fresh air ventilation per person for any type of building is 8 l/s which is able to dilute the CO2 concentration inside the envelope and maintain it around 700 ppm, the Swedish BBR standard has a slightly different definition for ventilation rate. According to this standard, the minimum ventilation rate for a building is 0.35 l/s.m2 of living area. To get the desirable and acceptable indoor climate proper ventilation units should be installed correctly to introduce the fresh air and reject the exhausted aged air that has accumulated inside the house [47], [51].

Besides, all buildings are in need of temperature control to acquire an acceptable indoor climate. Air handling units or AHU is another complicated system equipped with cooling and/or heating coils and air filters that are dedicated to cover the cooling, heating, humidification and dehumidification demands for the different zones in buildings. AHUs can easily process the outside air before it reaches the indoor area according to the demand.

For hot and humid climates like Accra, there will be no need to turn on the heating coil since the outdoor temperature never drops under 23 °C around the year Figure 40. In contrast, the cooling coil should constantly operate to diminish the humidity content and reject unnecessary amount of water vapor and heat entering with the fresh air. According to ASHRAE standard maintaining the relative humidity in hot and humid climates to around 50% is desirable and more convenient [47]. However, the initial costs and high energy consumption of AHUs can be a reason to avoid using them in small residential buildings like our project with only 140 m². Thus the utilization of private ventilation (PV) and small scale supply and exhaust ventilation systems with heat/cold recovery (FTX) units can be seen as an alternative to huge and costly AHU systems. Figure 20 shows the schematic of a AHU and PV system which are working together to provide a better indoor climate for occupants in an office building in a hot and humid area [68].

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31 FIGURE 20 SHOWS AHU AND PV SYSTEMS WORKING TOGETHER IN A HOT AND HUMID ARE [68]

However, another important factor of infiltration should be taken into consideration when dealing with ventilation rates and fresh air requirement. To our knowledge houses with an average and bad insulation have higher infiltration air change per hour (ACH) than in tight and well-insulated houses. In the following parts of the report we will show how variations in ACH can change the indoor climate radically in terms of CO2 accumulation and amount of the fresh air.

Exhaust and supply air ventilation with heat recovery (FTX system)

This energy efficient system performs well regardless of the weather and can supply large amounts of fresh ventilation air to the different zones of a building. There are two fans one for exhaust and one for supply air. If the FTX system is designed for heat recovery the entire process can be expressed as below. The exhaust air is drawn from the utility room, kitchen and bathroom, which have higher temperatures and the supply air is sent to bedrooms, living rooms and the studio in the central unit of the FTX. There is a heat exchanger in which the warm exhaust air energy is transferred to outdoor. The whole process can save a heating energy of 50 to 60% in comparison with ventilation systems without heat recovery unit. The only thing is the maintenance of the unit in even intervals of 1 year to change the dust and pollutant filters and clean the diffusers from unwanted accumulations of dust and other substances [69], [70].

However, in the very cold days of the year, the heating energy passed from exhausted indoor air to fresh outdoor cold air may not be sufficient to get the desirable temperature before introducing the ventilated air to the zones.

Thus, there is a need for a heating coil to process the supply ventilated air temperature and rise it to the desired set point. Also, there will be some interruptions during the very cold days which is due to defrosting of the FTX coils for some minutes per hour [70].

Humidity Control of the Fresh Air in Hot and humid Climates

In contrast with the heat recovery FTX system which is equipped with heating coil or electric heater, the FTX units planned installation in hot and humid climates should be equipped with a cooling coil to reduce the

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32 temperature and humidity of the supplied ventilated air [71]. Obviously, the efficiency of the cold recovery FTX unit will be lower than the efficiency of the heat recovery FTX units due to the high temperature of the exhaust air entering the heat/cold exchanger. However, the main reason to utilize this technology can be to provide acceptable amount of fresh air to the zones, and reduce the CO2 levels inside the occupied rooms by dispatching the aged and exhausted air from them. Also, the cooling coil of the FTX system can be connected to the chiller unit of the fan coil system or outdoor unit of the VRF air conditioning system which is situated outside of the house [34].

According to psychrometric data, dew point will be higher if the temperature and humidity are both high. At surface temperatures below those dew points, the risk of condensation and water damage is too high. Therefore, having a cooling coil in connection with FTX ventilation is crucial and a must have factor. Figure 21 show the different dew points for different temperatures and humidity ratios.

FIGURE 21 SHOWS RELATIONSHIP BETWEEN DIFFERENT DEW POINTS, TEMPERATURE AND RELATIVE HUMIDITY AT 1 BAR ATMOSPHERIC PRESSURE [72]

Figure 22 demonstrates the schematic of the cooling coil unit of the AHU system installed in hot and humid area [71] while Figure 23 shows a heat recovery FTX ventilation system which is used very commonly in Sweden [70].

The illustration shows a FTX system with following components and functions. No 1. Fresh outdoor air is introduced, supply air. No 2. The cold supply air is heated in a heat exchanger using the extracted warm room air, exhaust air. No 3. The heated supply air is distributed in the house. No 4. The polluted exhaust air is extracted from the kitchen and bathroom. No 5. The exhaust air gives up its heat to supply air in the heat exchanger and flows out.

Sustainability & Economical Evaluation of the Smart and Energy Efficient Technologies for the Rammed-earth House in Accra Ghana

Master Thesis