FACULTY OF ENGINEERING AND SUSTAINABLE DEVELOPMENT
Department of Building, Energy and Environmental Engineering
Heat balance of a historical church Transmission losses
Maider Galarraga
June 2014
Master Thesis in Energy Systems, 15 credits Supervisor: Magnuss Mattsson
Examiner: Ulf Larssson
PREFACE
The author of this thesis wants to express her sincere gratitude to the following people, who in a special way at a certain moment of this long experience have rendered their assistance and support for the accomplishment of her dream.
Magnuss Mattsson, my thesis supervisor, for providing necessary information, for sharing his knowledge and for his disposition.
Jose Ignacio Blanco, for his dedication, confidence and support during these years.
Edorta Gamboa and Leire Herrero, for their support, advise and time.
And most of all, my beloved parents, and my beloved friends for their never ending encouragement and care.
Finally, I would like to dedicate this piece of work to my beloved
grandmother.
ABSTRACT
The structure of old monumental buildings differs a lot from contemporary buildings. The structural materials were wood, bricks and stone. Originally these buildings had no heating and for centuries the indoor climate was mainly determined by the outdoor climate. Due to rapid changes in society the demands of the churchgoers vary in the last decades. As a consequence of the high thermal comfort in modern day buildings, this was also required in churches. Thus, in a large number of churches heating systems were installed.
In this project transmission losses from Hamrånge church have been studied. For this purpose transmission through walls, windows and floor has been analysed. Besides, a comparison between air infiltration losses, solar heat gain and transmission losses has been carried out in order to give a wide overview about the energetic performance of the building.
The methodology used could be defined as repetitive due to the similarity of the formulas utilized. For the energetic analysis of the church, temperature, humidity and sun irradiation sensors have been installed in the church. Besides, one-year basis has been established for transmission losses calculation: from 12/10/1 to 13/09/30. That way, the comparison with air infiltration losses and solar heat gain has the same time frame.
As a result, the superiority of the transmission losses has been noticed together with the positive influence of solar heat gain during summertime. Besides, the variation of the heating power curve has been clarified too. Moreover, after studying the energetic performance of the church restoration opportunities could be considered.
However, in historical buildings such as Hamrånge church, any change should lead to
the preservation of the building itself.
TABLE OF CONTENTS
Page
1. INTRODUCTION... 1
2. THEORY...4
2.1 Transmission losses characterization……...4
2.2 Transmission through walls and floor...9
2.3 Transmission through windows...11
2.4 Thermal capacity of materials……….………..13
3. METHOD...14
3.1 Methodology……….14
3.2 Limitations………..………..17
3.3 Measurement devices……….……...………18
4. RESULTS...20
4.1 Hamrånge church transmission losses……….20
4.2 Air infiltration and solar heat gain…...……….………...23
4.3 Heat balance of Hamrånge church………..…….25
4.4 Solar heat gain and transmission loses through windows………26
4.5 Heat buffering of materials………..27
5. DISCUSSION...28
6. CONCLUSION...32
7. REFERENCES...33
8. APPENDIX...36
1 HEAT BALANCE OF A HISTORICAL CHURCH:
TRANSMISSION LOSSES
1.1 Background
The structure of old monumental buildings differs a lot from contemporary buildings. The structural materials were wood, bricks and stone. In order to construct high buildings with huge spans, thick massive walls and many massive columns were needed.
Originally these buildings had no heating and for centuries the indoor climate was mainly determined by the outdoor climate. Because of the massive walls, the large indoor air volume, the relatively small windows and most often relatively limited natural ventilation, the indoor climate was much more stable than the outdoor climate. There was hardly a difference between the day and night temperature. In summer the indoor air climate was cool compared to outdoors, in winter indoor conditions were warmer.
Due to rapid changes in society the demands of the churchgoers vary in the last decades. As a consequence of the high thermal comfort in modern day buildings, this was also required in churches. Thus, in a large number of churches heating systems were installed. Further researches have shown that heating installations cause great building physical impact. This may lead to the deterioration of the building itself and its interior. [1]
Nowadays, the number of churches and chapels owned by the Church of Sweden is 3381. The Swedish Heritage Conservation Board protects up to 2953 churches [2]. As this organization has explained, the care and preservation of Swedish cultural environment is a matter of national concern. [3] Therefore, when restoration is needed, it should be developed considering preservation, energy requirements, thermal comfort and aesthetics at the same time. Concerning statements before, the energetic performance of these type of buildings is, therefore, aim of study.
1.2 Previous studies
With the objective of quantifying the damage occasioned to church buildings due to the installation of heating systems, studies among European countries have been developed [4].
In those researches the principal consequences between heating and no heating have been described. Also the harm caused in churches has been studied such as the damage in organs and ceiling contamination. [5] For that purpose, air temperatures, humidity, ventilation rates…were measured. Afterwards, and with the help of simulation programs, analysis was carried out and then results were pointed out.
The most important conclusion has been that heating monuments has a positive effect on the preservation of the building and its interior. However, the restriction stands for not heating continuously to reach the level of thermal comfort [6].
Although this thesis is just focused in the calculation of heat losses, anterior studies could offer a perspective of the importance of improving the heating systems.
Thus, a reduction of losses would imply a reduction of the needed heating power and hence, less damage to the building.
Figure 1. Church organ. Temperature distribution
1.3 Scope
In this project transmission losses from Hamrånge church have been studied. For this purpose not only walls and windows have been analysed, but also the thermal capacity of construction materials and some other associated effects. Besides, a comparison between air infiltration losses, solar heat gain and transmission losses has been carried out in order to give a wide overview about the energetic performance of the
building. That way, the first steps for further restoration possibilities will be established.
The church under study is located on a hill 30 km north from Gävle, at Bergby village. In relation to previously mentioned, church walls are made of stone and plastered on inside and outside. Apparently, stone and lime mortar have been used to fill the interior side. In addition, the windows at the church are double-glazed and the floor is composed by wood and lime sand layers.
When measurements were done, different devices were used such as thermistors, humidity sensors and sun irradiation sensors. For transmission losses calculation data given by indoor air, walls and window temperature sensors has been used principally.
Moreover, a period for the calculations has been settled: from 1st of October 2012 to 30th of September 2013. That way, the three energy categories have the same basis, which will lead to higher accuracy in results and comparisons.
The following picture shows the east facade of the church:
Figure 2. Hamrånge church
2 THEORY
2.1 Transmission losses characterization
Before explaining transmission losses and their way of calculation, it has been considered necessary to provide the reader definitions and concepts that will be used throughout this work. Doing so, it is intended to provide a better understanding of this concept.
Heat transfer theory
Heat transfer takes place by three different mechanisms:
conduction, convection and radiation, with the direction of net heat flow always going from the higher temperature to the lower one. A building loses or gains heat by the previously mentioned mechanisms, with the amount of heat transferred by each depending on the construction of the building envelope. The building steady-state heat balance can be expressed as:
𝑄
!!"#$%&+ 𝑄
!"#$%"&'_!!"!_!"#$= 𝑄
!"#$+ 𝑄
!"#$+ 𝑄
!"#$"%$&' (1)Below the main features of heat transfer mechanisms are explained:
Conduction
Heat transfer by conduction refers to the energy that is transferred when vibrating atoms collide and free electrons move collectively. It takes place every time there is a temperature difference between two sides of a material, or two or more different solids in contact. This mode also intervenes when there is heat transferred in gases and liquids and in the contacts between a solid at one side and liquids/gases at the other. The heat transfer rate by conduction through a building component is usually expressed as:
𝑄
!"#$= 𝐶 ⋅ 𝐴 ⋅ (𝑇
!"− 𝑇
!"#)
[W] (2)In equation (2) C =λ/d (W/m2K) is the thermal conductance of the material; A [m2] is the surface through which heat is being exchanged and
(𝑇
!"− 𝑇
!"#)
is the temperature difference between the two sides of the element (K). Besides, λ (W/m K) is the thermal conductivity of the material and d is its thickness.Convection
Convection is a mechanism of heat transfer occurring by observable movements of fluids that carry the heat from one place to another. In buildings, air movements normally cause this. Fluids expand when they gain heat and contract when they lose heat.
To consider convection as the heat transfer mechanism fluid in contact with the surface must be in motion; if not, the mode of heat transfer is conduction. If an external force is the responsible of the motion of the fluid (e.g., fan, pump, wind), forced convection has occurred. If fluid motion results from buoyant forces caused by the surface being warmer or cooler than the fluid, it is natural convection.
The equation used to calculate convective heat transfer is:
𝑄
!"#$= 𝛼 ∙ 𝐴 ⋅ (𝑇
!− 𝑇
!)
[W] (3)In this expression
𝛼
is the convective surface heat transfer coefficient (also denoted as h);(𝑇
!− 𝑇
!)
is the temperature difference between the surface and the ambient air (K), and A is the area of the surface (m2).Radiation
Radiation refers to heat transfer caused by the emission and absorption of electromagnetic waves. All the surfaces above absolute zero emit electromagnetic energy, and when these waves strike another surface, part of the energy is reflected, part is absorbed and sometimes part can be transmitted, depending on the characteristics of the surface. All these emissions result in heat exchange between surfaces at different temperatures.
The equation to determine transferred heat by radiation is:
𝑄
!"#= 𝜎 ⋅ 𝐴 ⋅ (𝑇
!!− 𝑇
!!)
[W] (4)In the expression above
𝜎
refers to Stefan-Boltzmann constant,(𝑇
!− 𝑇
!)
is the temperature difference between the surface and the ambient air (K), and A is the area of the surface (m2).Thermal performance of a building
With the purpose of encouraging energy conservation in buildings each structure is given an energy efficiency rating. This takes into account a number of factors, including the heating system, the insulation in a building and the amount of energy used for space heating.
In order to conserve the energy used for space heating, the amount of heat lost through the envelope of a building should be kept to a minimum The standardised, calculated measurement of heat loss for all building materials is known as a U-value.
U-value
The U-value is the amount of heat lost (conducted) every second, across 1 m2 of material, for every degree difference in temperature between two surfaces in a steady state.
Since the envelope in a building consists of multiple elements, for a standardised calculation of heat loss, a U-value rating is calculated for each element or material. A lower U-value indicates a slower rate of heat loss, therefore the more energy efficient the element is considered to be.
The energy (heat loss) is measured in watts per meter squared (W/m2K) and U- values are calculated using materials’ thermal resistance.
Thermal Resistance (R) is a measure of the ability of a material to resist the passage of heat. It is measured in m2 K/W, and in practice is the inverse of thermal conductance (C).
Thus, U values will be calculated as follows:
𝑈 =! !
!"! !!!!!" [W/m2K] (5) 𝑅! =!!!
! [m2K/W] (for conduction resistances)
Where 𝑑! is the thickness of the surface and Rsi and Rse are internal and external surface resistances, which will be explained in the following section.
Related to what has been mentioned at the beginning of this work, the following table shows values of thermal conductivity for stone, brick and wood, church construction materials indeed [7].
Table 1. Thermal conductivity of church construction materials [8]
Material Thermal Conductivity (W/mK)
Stone (basalt, granite) 2,33
Building brick 0,73
Wood (softwood/hardwood) 0,12/0,17
Surface heat transmission coefficient
The surface heat transmission coefficient (hi and he [W/m2K]) indicates the heat that is being transferred from or through a surface in contact with a fluid per square meter. It comprises conduction, convection and radiation effects. This property is multi-factor dependant: air movement, surface roughness or ambient temperature will influence its value.
As mentioned, if the inverse of this parameter is obtained surface resistance is found out.
Conduction and convection combination
When conduction and convection appear simultaneously they should be considered in the global heat transfer coefficient calculation. Thus, thermal resistances for conduction and convection should be got and then added
[9]. Afterwards, U-value will be obtained as following:
UTot=1/RTot;
RTot= RCOND+RCONV (6)
RCOND= d/λ
[m2K/W]; RCONV= 1/h
Energy balance of a building
Energy can be supplied and consumed in different ways and for different purposes. Generally, the energy that is supplied should be equal to the energy that is being consumed.
According to the Second Law of Thermodynamics, heat flows spontaneously from a material at a higher temperature to the one at a lower temperature. Therefore, in the presence of a difference between indoor temperature and outdoor temperature, heat may be conduced to the outside since indoor temperature is warmer than outdoor temperature.
Heat losses through building envelope consist of transmission losses through walls, windows, roof, floor and so forth. Ventilation losses are divided into two different types: mechanical ventilation losses and natural ventilation losses, and finally heat losses of hot top water. Correspondingly, the heat supplied to compensate losses consists of solar radiation, heating systems and internal heat. This last one includes heat from equipment, lighting and people inside the building.
The heat balance is represented with the following equation:
𝑄!"#$%+ 𝑄!"#.!"#$+ 𝑄!"#.!"#$+ 𝑄!"#= 𝑄!"#+ 𝑄!"#+ 𝑄!" [W] (7)
Where,
𝑄!"#$%à Transmission losses through the building envelope
𝑄!"#.!"#$à Mechanical ventilation losses
𝑄!"#.!"#$à Natural ventilation losses (air leakage, infiltration)
𝑄!"#à Heat demand for domestic hot water
𝑄!"#à Heat gained due to solar radiation through windows
𝑄!"#à Internal heat gain (lighting, occupants, electrical devices)
𝑄!"à Space heating
As in this project only the transmission losses of the church have been analysed, a deeper analysis of them has been carried out.
Transmission losses
Temperature and pressure differences between the outdoor and indoor air result in a transfer of heat through the building envelope. Heat is lost to outside by transmission due to temperature differences. Infiltration occurs through e.g. leaky window frames, door cracks etc. and means that a large amount of outdoors air enters so extra heat has to be supplied to warm up the relatively cold air to the indoor temperature. The insulating properties and the air- tightness of the building envelope will determine how much heat will be exchanged.
Transmission losses calculation could be described as:
𝑄!"#$%= (𝐴 ∙ 𝑈) ∙ (𝑇!"− 𝑇!"#) [W] (8)
Where,
A: Is the area of studying [m2] U: Heat loss coefficient [W/m2K]
Tin and Tout: indoors and outdoors temperatures [K]
2.2 Transmission through walls and floor
It is important to define conduction as the main heat transfer mechanism through walls and windows. As a generalization, it will be considered that different layers compose the element under study. To calculate the heat transfer the next suppositions will be assumed:
- Temperatures of the surfaces are constant.
- A, λ and d are known features.
First of all, the theory for a single-layer element will be analysed. After that, and realizing the similarity between single-layer and multi-layer cases, results will be extrapolated.
To start, lets consider the equation !!"!!!+!!"!!!+!!"!!!= 0 for steady state.
After operating, the expression for the one-dimensional thermal field is derived:
𝑇 = 𝑇!−!!!!! !⋅ 𝑥 [K] (9) Where T is used to express temperature, d is the thickness of the layer and x is used to denote a distance from an axis.
After that, Fourier’s Law is used to determine the amount of heat transferred by conduction through the element. It should be integrated to obtain the expression below:
𝑄 = −𝑘 ⋅ 𝐴 ⋅!"
!" → 𝑄 = 𝐴 ⋅!!!!! !
!
[W] (10)
In this equation !
! [m2K/W] is the thermal resistance and 𝑇 [𝐾] is used to denote temperature. [10]
There is an electrical analogy with conduction heat transfer that can be used in problem solving. The analogue of heat is current, and the analogue of the temperature difference is voltage difference. That way, the concept of thermal resistance circuits appears. This is the methodology to follow when more than one layer composes the element. [11]
Figure 3. Series thermal resistance circuit
In the composite slab shown in figure 2 the heat flux is constant with x, the resistances are in series so that they sum R=R1 +R2, and TL and TR are the temperature at the left and right sides respectively [12]. Thus, the heat transfer rate is given by:
𝑄 =
!!!!! !=
!!!!!!!!!!
[W/m
2] (11)
2.3 Transmission through windows
Heat transmittance through a window is not a simple process. It is determined by the radiation and conduction of the different materials and convection between materials used to manufacture the window. Therefore, a combination of conduction, convection and radiation should be done to get the total heat transfer. When talking about windows there is a concept that should be highlighted: fenestration.
Fenestration is an architectural term that refers to the arrangement, proportion, and design of window, skylight, and door systems in a building. Fenestration can serve as a physical and/or visual connection to the outdoors, as well as a way to admit solar radiation for natural lighting, and for heat gain to a space. Fenestration can be fixed or operable, and operable units can allow, for instance, natural ventilation to a space. [8]
Fenestration affects building energy use through four basic mechanisms:
thermal heat transfer, solar heat gain, air leakage, and day lighting. The energy effects of fenestration can be minimized by [13]:
1. Using daylight to balance lighting requirements.
2. Using glazing and shading strategies to control solar heat gain to supplement heating through passive solar gain and minimize cooling requirements.
3. Using glazing to minimize conductive heat loss.
4. Specifying low-air-leakage fenestration products.
5. Integrating fenestration into natural ventilation strategies that can reduce energy use for cooling and fresh air requirements.
Fenestration includes several components from which glazing units and frames are principally distinguished. A glazing unit may consist of a single glazing or multiple glazing. These last ones are commonly called insulating glazing units. The most common material for those is glass. Clear glass transmits more than 75% of the incident solar radiation and more than 85% of the visible light. [8]
Furthermore, there is a variety of window framing materials such as wood, metal, and polymers. Wood has good structural integrity and insulating value but low resistance to weather, moisture and organic degradation. This is the frame material used in the windows of Hamrånge church.
Regarding energy, it flows through fenestration in several ways:
conductive and convective heat transfer caused by the temperature difference between outdoor and indoor air, long-wave (above 2500 nm) radiation between the fenestration and its surroundings and between glazing layers, and short-wave (below 2500 nm) solar radiation incidence on the fenestration, either directly from the sun or reflected from the ground or adjacent objects.
It should be pointed out that in this thesis only conduction and convection heat transfer mechanisms have been treated. The heat gained due to solar radiation belongs to another study. [14]
U- factor (thermal transmittance) for windows
In the absence of sunlight, air infiltration, and moisture condensation the heat transfer rate through a fenestration system follows this equation:
Q = U*Apf
*(T
Out– T
In) [W] (12)
Where
Q = energy flow (W)
U = overall coefficient of heat transfer (U-factor) (W/m2K) Apf = total projected area of fenestration (m2)
TIn = indoor air temperature (K) TOut = outdoor air temperature (K)
Most fenestration systems consist of transparent multipane glazing units and opaque elements forming the frame. The glazing unit’s heat transfer paths are subdivided into centre-of-glass, edge-of glass and frame contributions. Consequently, the total rate of heat transfer through a fenestration system can be calculated knowing the separate contributions of the mentioned parts. The overall U-factor is estimated using area-weighted U-factors for each contribution by:
U
0=(U
cg*A
cg+U
eg*A
eg+U
f*A
f)/A
pf[W/m
2K] (13)
To give an end to this section the complexity of the heat transfer through a window is illustrated.
Figure 4. Heat transfer through windows [15]
2.4 Thermal capacity of materials
The thermal capacity of materials is denoted as Ct [J/m3 K]. This property has great influence in steady state heat transmission processes. It will determine what is know as thermal inertia, a concept that is influenced by the delay and attenuation of the heat wave at the same time. Besides, it will contribute to the thermal stability of the interior of buildings.
The specific heat γ [J/Kg K] is one of the factors that will establish the thermal capacity of materials. The similarity between values of this feature is notorious among construction materials. For instance, organic materials are ranged between 900- 1500 [J/Kg K]. In contrast, water stands out among them. It has a value of 4184 [J/Kg K].
Therefore, it means that the heat capacity of materials could increase depending of the amount of water each material contains. [16]
In addition, not only the specific heat contributes to the definition of this idea but also the density has to be outlined. It is considered to be the main factor when obtaining thermal capacity.
The total heat capacity of a building envelope [J/m2 K] is proportional to its thickness. Usually, dense materials have high thermal capacity, but are good thermal conductors too. As a result, large material thicknesses should be installed in order to achieve proper insulation. Commonly, heavy materials have low insulation but lot of thermal inertia. On the contrary, lightweight construction has just the opposite characteristics [17].
3 METHOD
3.1 Methodology
First of all, it is important to define the methodology used as repetitive.
The repetitiveness has appeared due to the usage of similar formulas for the calculation of transmission losses through church windows, walls and floor. As in previous sections explained, this components share similar expressions regarding heat transmission. The prior differences remain in the temperature gradient, the area and the heat transmission coefficient value. Besides, U-value depends on material properties and on the way in which heat has been transferred.
For the energetic analysis of the church, temperature, humidity and sun irradiation sensors have been installed. The task was responsibility of the personnel of the University of Gävle. To give an idea, along a mast 12 indoor air temperature sensors were placed. Moreover, along a wall 6 sensors were pasted too. Besides, ceiling and crawl space surface temperatures were also taken. Finally, 2 separated sensors were glued on a window glass.
Furthermore, extra information has been provided. For instance, the plans of the church, its position, data of construction materials, weather information and the accurate position of every measuring sensor were given.
The picture below shows the placing of some measurement systems:
Figure 5.Measuring sensor distribution along a mast
It is important to clarify that for transmission losses calculation temperature is the useful parameter among others. In fact, temperature differences and averages have been calculated for the main objective of the thesis.
The information given by the sensors was captured in data loggers. From those 7 files were extracted dating values from 12/08/09 to 13/10/07. As said, one-year basis has been established for transmission losses calculation: from 12/10/1 to 13/09/30.
That way, the comparison with air infiltration losses and solar heat gain has the same time frame. It is important to point out that all the files provided had not the same time division. For that reason, an average hourly value has been selected in order to simplify the huge range of data and make the calculations in an hourly basis. Thus, 8760 temperature values have been utilized.
Apart from the data provided from data loggers, information about weather has been given too. In two different files, temperature for Hamrånge and Gävle was plotted together with wind speed and humidity values. This information has been used to get outdoor temperature. Due to the absence of information to complete the whole year a combination of both files has been done. Furthermore, information from a weather webpage has been necessary to complete last month temperature values. [18] The following pictures shows what the information provided by data loggers look like:
Figure 6. Example of data provided by loggers. Air temperature sensors placed on the mast. Recording every 2 minutes
Figure 7. Hourly values for wall placed sensors. Wall temperatures
Once all the temperature values were selected, the corresponding temperature averages for indoor air, wall and window surfaces have been done. For their obtaining, the differences between sensor heights have been considered and then a height- weighted average has been calculated. As an example, wall temperature has been got as following:
T= (W1*0,8+W2*1,2+W3*1,7+W4*2+W5*1,5+W6*1,45)/9,9 Where
Height of W1= 0,6 m; Height of W2=1,6 m.
ΔH1=(1,6-0,6)/2+(0,6/2)=0,8 Total height of the wall=9,9 m.
After that, areas and heat transfer coefficient values have been obtained.
The calculation of the areas has been executed using the plans and choosing the sizes for each element. However, more details have been necessary to recognize when U-values were analysed. As explained before, when a combination of conduction and convection appears thermal resistances for both should be taken into account. Even if it is not a hard task, collecting values for convection heat transfer coefficient has not been easy.
Continuing with the process, and once all the data has been collected, heat transfer calculations have been carried out. Firstly, transmission losses through walls have been obtained. Secondly, heat losses through floor have been got. And finally, transmissions losses through windows have been attained. For all those calculations equation (8) has been used. These are the assumptions made for the calculus:
1. Combined conduction and convection in walls.
2. Combined conduction and convection in windows.
3. Combined conduction and convection through floor.
The principal difference regarding heat loss calculation remains in U- value. Hence, for walls and floor equation (6) has been utilized. For windows a webpage has been checked. [19] It has been realized simpler than using equations written in paragraphs above. Nevertheless, there are simple double-glazing windows so that the selected U value could be defined as common.
With the aim of showing the results in a clear and tidy way, and in order to make the comparisons as accurate as possible, various charts have been generated. Thus, next graphs have been plotted:
1. A chart containing hourly values of heat losses.
2. A chart showing total heat loss during a month.
3. A chart containing two 5-day periods, on February and April.
To give an end to this paragraph, it should be mentioned how the information about the total heating power of the church has been managed. The current to the heating units was measured by connecting current measuring clamps (Metrel d.d., Horjul, Slovenia) to each of the three main electricity phases. The measurements of church total heating power were written giving values for every minute since 12/06/20 until 13/10/15. Accordingly, values for the selected one-year-period have been chosen together with hourly value selection. After that, monthly and 5-day averages have been obtained.
So, this has been the methodology followed in this thesis. All what has been done has given opportunity for reflexion and has aided in conclusion making process.
3.2 Limitations
In this section the limitations of the project will be cleared. It is of great importance to recognize the uncertainties in the calculations of transmission losses. Thus, the possible mistakes have been listed in the next points:
• A unique value has been selected as hourly average. Notice that most of the data is given every couple of minutes.
• Even if building materials are defined, it has been unfeasible to get the U-value for some heterogeneous elements. For example, the walls of the church are made of stone a lime mortar. In this case, stone has been chosen as the main component.
• For windows simplifications have been made. Thus, the frame has been neglected and for the total area the sum of single glasses has been made (per each window).
• As explained at the beginning of this section, and due to the lack of data, some file combination has been done in order to get temperature values for the whole year. This is the case of the outdoor temperature. Apart from this, a weather webpage has been checked. Therefore, there are days that have the same value along 24 hours.
• For wall and window area obtaining building middle height has been taken. It is also a restriction due to the fact that the church is unstable regarding this particular size.
• Finally, Microsoft Excel has been used as the main calculation tool. Although the results are precise, the utilization of some simulation program would have lead to more detailed information.
All what has been mentioned will have an influence in the final result.
Even though, the calculation of transmission losses through windows, walls and floor are considered accurate enough to make conclusions and discuss whether heat is being lost in huge proportion.
3.3 Measurement devices
It has been considered interesting to add this section in order to give the reader a concise list of all the equipment used in the measuring process. Thus, their principal features will be explained providing a bit of knowledge about them.
•
Thermistors: temperature-measuring sensors. They have been placed along wall surface, mast, and window. They have been also glued in church benches. It’s a type of resistor that varies its resistance with temperature changes. There are usually made of polymer or ceramic materials. They achieve a higher precision within a limited temperature range. The utilized thermistors are 47 mm in diameter and 4 mm long.•
Sun irradiation sensor: “Sunshine pyranometer”, SPN1. It is placed on the top of the church roof. Its sampling and storage intervals are of 5 seconds and 2 minutes, respectively.•
Data loggers: “Grant data-logger” and “ELTEK SQ851-WXT”. It is an electronic device that records data over time or in relation to location either with a built in instrument or sensor or via external instruments and sensors. Increasingly, but not entirely, they are based on a digital processor. Generally they are small, portable, and equipped with a microprocessor, internal memory for data storage and sensors.•
Weather transmitter: Vaisala weather transmitter WXT520.Placed 17 metres over ground on a mast 1 km Northwest of the church.
The following pictures show some measuring equipment:
Figure 8. [CO2] measuring
4 RESULTS
Throughout this section results will be presented. All the details of required information for transmission losses calculation is shown afterwards in the appendices.
4.1 Hamrånge church transmission losses
In order to present clearly what has been obtained not only heat loss values will be displayed but also graphs and few comments.
To begin with, transmission losses through walls will be presented. As explained, graphs containing hourly and monthly values will be shown.
Figure 10. Time history of hourly averaged transmission losses through walls
Figure 11.Time history of monthly losses through walls -‐20
-‐10 0 10 20 30 40 50 60
kW
0 5000 10000 15000 20000 25000
kW
In Figure 10 transmission losses through walls during 365 days are represented. As it could be noticed, the maximum value stands for almost 60 kWh and the minimum is under zero, which means that the heat flow is in the opposite direction: from the outside to the interior of the church.
For the obtaining of monthly values a sum of the daily heat losses has been carried out for each period. These types of charts are useful when comparing transmission losses with church’s total heating power.
As for walls, same charts will be shown for the floor.
Figure 12. Time history of hourly averaged transmission losses through floor
Figure 13. Time history of monthly heat losses through floor
Heat transfer through floor has its maximum and minimum around December and September, with values around 12 and 2 kWh respectively.
0 2 4 6 8 10 12 14
kW
0 1000 2000 3000 4000 5000 6000 7000
kW
Similarly, the following charts have been obtained for heat transfer through windows.
Figure 14. Time history of hourly averaged transmission losses through windows
Figure 15. Time history of monthly losses through windows
Following the same pattern of walls, heat loss through windows also has a negative minimum value what means that the heat flux is flowing in the opposite direction. Nevertheless, this heat gain is little enough to lead to significant changes on the heat balance of the church. The maximum value amounts to be 12 kWh.
It is important to point out that losses through fenestration, and especially through windows and doors, are considered risky in the way that they used to be of high.
In this case, December appears to be the month in which the losses are higher, and staring -‐4
-‐2 0 2 4 6 8 10 12 14
kW
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
kW
at hourly averaged graphs, window and floor maximums are similar in numbers, 12kWh each.
To summarize, total transmission losses are shown. In the same way as before, a graph covering monthly values is attached.
Figure 16. Time history of monthly averaged transmission losses
As it can be easily understood, the higher the temperature difference between outdoor and indoor air, the higher the losses through walls, windows and floor.
This fact could be checked when looking at the maximum and minimum values of the chart. As seen, the peak occurs around December, when is common to have great differences in indoor-outdoor temperature, and March. As it is not common to have lower temperature differences in March than in February, this fact has been corroborated. Thus, the averaged temperature gradient is 14ºC in February whereas in March amounts to be almost 20ºC. Hence, a possible mistake in calculation has been eliminated.
In addition, graphs belonging to floor and wall heat loss have been contrasted just because the maximum values tend to appear in December and March too.
In contrast, around June transmission losses have its minimum, when the temperature difference tends to be lower.
4.2 Air infiltration and solar heat gain
As mentioned in the first paragraphs, a heat balance of the church has been performed. For that, transmission losses, air infiltration losses and solar heat gain have
0 5000 10000 15000 20000 25000 30000 35000
kW
been analysed. Even though among this project only the first type of losses are studied, the results for the other two energy categories have been provided. [14][20]
Hence, the results for air infiltration losses are shown in the following graph.
Figure 17.Time history of monthly averaged air ventilation losses
In the next graph monthly values for solar heat gain have been plotted, where is feasible to identify the peaks during summertime.
Figure 18. Time history of monthly averaged solar heat gain 0
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
kW
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
kW
4.3 Heat balance of Hamrånge church
Focusing on the heat balance of the church the contribution of each energy category has to be identified. While transmission and ventilation losses have a negative connotation as they are considered “ losses”, solar heat gain has a positive influence. As a result, the graph shown in figure 19 has been obtained. For its calculation the next principle has been applied:
Heating Power = Ventilation + Transmission – Solar heat gain
Figure 19. Heat balance of Hamrånge church
With the aim of providing a deeper knowledge about the thermal performance of the church two 5-day periods have been studied. The mentioned periods have been selected taking into account solar radiation effects. Hence, the first one has been chosen on February and the second one on April, when there are great variations of sun hours and irradiance.
Here the results for 1st 5-day interval are shown. It should be pointed out that on February there are less hours of sun.
0 10000 20000 30000 40000 50000 60000
kW
Losses
Heating Power
Figure 20. Heat balance of the church on February
Continuing with the analysis, the following result has been obtained for 5- day interval on April:
Figure 21. Heat balance of the church on April
4.4 Solar heat gain and transmission losses through windows
As commented before, solar radiation is a source of heat to take advantage of. Thus, it could be possible to supply a part of the heat that has been lost. As its contribution is not high, it could be possible to equalise with the heat that is being transferred through windows. To give an approximation a chart of solar heat gain has
-‐5 0 5 10 15 20 25 30 35 40
01/02/13 00:00 08:00 16:00 02/02/13 00:00 08:00 16:00 03/02/13 00:00 08:00 16:00 04/02/13 00:00 08:00 16:00 05/02/13 00:00 08:00 16:00
kW
Heating Power (+) Transmission losses (-‐) Air In9iltration losses (-‐) Solar Heat (+)
-‐20,00 0,00 20,00 40,00 60,00 80,00 100,00 120,00
01/04/13 00:00 08:00 16:00 02/04/13 00:00 08:00 16:00 03/04/13 00:00 08:00 16:00 04/04/13 00:00 08:00 16:00 05/04/13 00:00 08:00 16:00
kW
Heating Power (+) Transmission losses (-‐) Air In9iltration losses (-‐) Solar Heat (+)
Figure 22. Window heat flow and solar heat gain
In figure 22 is clearly defined the variation of solar heat gain among the year under study. Whereas until February losses through windows cannot be complemented by the influence of the sun, the opposite pattern has been established from March on. Thus, the superiority of solar heat gain could be used to block the losses through windows.
4.5 Heat buffering of materials
To give an end to this paragraph the heat buffering of materials has been studied. As explained before heat buffering effects appear due to the capacity of materials to store heat. Hence, the possibility of church construction materials to store heat has been analysed. For that purpose the values obtained for 5 day intervals have been used.
The following graphs have been checked:
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
October Novembe Decembe January February March April May June July August Septemb
kW
Transmission windows Solar Heat Gain
0 10 20 30 40 50 60
kW Losses
Heating Power
Figure 24. 5-day interval on April 0
20 40 60 80 100
kW
Losses
Heating Power
5 DISCUSSION
In this section of the thesis the results are going to be explained. In addition, detailed comparisons will be performed too.
Regarding transmission through floor, there is a fact important to mention.
The heat that is going out through the floor is the responsible, at the same time, of preheating the air leakage coming from the crawl space. Consequently, it will have influence on the possible reduction of the total heating power needed for the church.
In what the three energy categories involve, similarities and differences could be pointed out: looking at figure 16 and checking the results obtained for ventilation losses the same pattern for both could be observed: during the cold months and due to the high temperature gradient between the inside and outside air of the church, the losses tend to be high and have their peak values. On the other hand, minimum values have appeared around June or July. The results have agreed, consequently, with heat transfer theory. [21] On the other hand, and due to the lack of sun, solar heat gain stands for minimum values during wintertime and maximum values during no-heating season, when the solar effect increases.
Concerning the heating power of the church, it appears to be enough to cover the necessities of the church, as shown in figure 19. However, there are a few points in which an extra or a lack of power has been detected. For instance, in November the extra heating is clearly shown whereas in February the lack of power is appreciated.
Possibly, a solution for eliminating the mentioned heat gaps could be a performance of an energy auditing to the church. By this, the energy needed could be precisely amounted for each period. Besides, new heating sources could be included and thus energy savings will appear. Another positive effect of this analysis will surely be the settlement of restoration possibilities.
For a deeper knowledge of the thermal performance of the church two periods have been selected and studied. The first one has covered the first five days of February 2013. The average temperature for these days has been around -3ºC [18]. Thus, and taking into consideration once more the heat transfer theory, it seems to be coherent for the heat flux to move from the inside of the church, which will be heated up to
guarantee the thermal comfort of the churchgoers, to the outside. It should not be forgotten that heat is going from higher temperatures to lower ones, form the interior of the church to the outside indeed.
Staring at figure 20, the superiority of the heating power has been appreciated for most of the period. This result is in agreement with the fact that the church should be heated up to deal with the losses. However, the existences of three heat gaps where losses are dominant have been noticed. A reason for this could be the absence of adjustment of the heating power curve. Doing so, the extra power could be used to supply the lack of heat. Moreover, solar heat gain has a poor influence among this period, a result that was expected, on the other hand.
Focusing now in the second interval, which covers the first five days of April, and having as a reference figure 21, a decrease in losses has been detected.
Besides, the heating power of the church is excessive for the last day of this period.
However, the power is not enough to manage the losses on the first four days. The influence of the solar heat gain is appreciated now. This fact is mainly due to the rise of hours of sunlight. It will contribute to diminish the losses and consequently, decrease the power needed by the church.
The solar heat gain has a positive effect on the heat balance. Due to this fact, it could be used as a sustainable source of heat. If its influence were used just to cover the losses though windows the following cost savings would have been obtained.
Even if it is just an approximation, it could give an idea of the amount of energy and cost that can be saved, and then make the installation of a solar system possible.
Table 2. Cost savings
MONTH ENERGY (kWh) PRICE (öre/kWh) SAVING (SEK)
March 3500 151[22] 5285
April 1900 2869
May 1500 2265
June 900 1359
July 800 1208
August 1000 151
September 1200 1812
TOTAL (SEK) 14949
To give an end to this paragraph the heat buffering of materials will be discussed. When the losses are high it means that the heat transfer through the element is flowing normally. This last statement could be noticed either on the first four days of
February or April, in figures 23 and 24, respectively. In contrast, when there is an excess of heat materials have favourable conditions to absorb it. Hence, apart from the heat that has been released to the outside, there is an excess of heat available to be absorbed by the material.
It should be important to point out that when air temperature differences between indoor-outdoor are higher the heat that could be retained by materials appears to be lower. It could be justified looking at the chart on figure 23 where losses are dominant.
Nevertheless, the energy storage is a matter under research and it has been many times studied in order to understand it and get the best materials for heat storing.
Energy storage technologies are a strategic and necessary component for the efficient utilization of renewable energy sources and energy conservation. Thermal energy storage (TES) in general has been a main topic in research for the last 30 years, but most researchers still today feel that one of the weak points of this technology is the material to be used as storage medium. [23]
6 CONCLUSION
Once transmission losses, air infiltration losses and solar heat gain have been analysed the heat balance of the church has been obtained. As a result, the superiority of the transmission losses should be highlighted together with the positive influence of solar heat gain during summertime. Besides, the variation of the heating power curve of the church has shown the excess and the lack of power among the year.
As once mentioned, a solution for achieving a balance concerning the needed power by the church could be the performance of an energy auditing. By this, the building is analysed in terms of used energy. [24] Besides, the energy required by the different unit processes will be defined and it will lead to energy saving measures and cost saving. Furthermore, as the losses are known the extra heat to be supplied will be known too.
Moreover, after studying the energetic performance of the church restoration opportunities have to be considered. It must be realized that for historical buildings such as Hamrånge church, any change should lead to the preservation of the building itself. Thus, extra limitations will appear when trying to update construction materials. However, making simple changes like crack covering or window changing will conclude surely, with loss reduction.
Finally, it is important to mention that studying transmission losses and comparing afterwards with the other two energetic categories not only has given the overview about the energetic performance of the church, but also has settled the results for further building renovation possibilities.
7 REFERENCES
[1] Schellen, Henk. Heating Monumental Churches: indoor climate and preservation of cultural heritage. Einhoven: Technische Universitiet Eindhoven, 2002. ISBN: 90-386- 1556-6.
[2] “ 2012 Review and Financial Summary for the Church of Sweden, National Level”.
[3] Heritage Conservation Board (KRFS 1989:15): Heritage Conservation Act.
(1988:950). Chapter 1, section 1. April 2002.
[4] Dario Camuffo, Emanuela Pagan, Sirkka Rissanen, Łukasz Bratasz, Roman Kozłowski, Marco Camuffo, Antonio della Valle. An advanced church heating system favourable to artworks: A contribution to European standardization. Journal of Cultural Heritage, Volume 11, Issue 2, April–June 2010, Pages 205-219.
[5] “ Bauphysikalische Untersuchungen in unbeheizten und beheizten Gebäuden alter Bauart” (Künzel 1991).
[6] Arroyo, Fátima, Villegas-Sanchez, Rosario. The church of Saint Martin (Trujillo, Spain): Study of stone degradation. Journal of Cultural Heritage, Volume 13, Issue 3, supplement, June 2013, Pages e109-e 112.
[7] Derbal, R., Defer, D., Cauchois, A., Antczak, E. A simple method for building materials thermophysical properties estimation. Construction and Building Materials, Volume 63, 30 July 2014, Pages 197-205.
[8] ASHRAE Handbook FUNDAMENTALS. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. 2009.
[9] Blingen, E. Conjugate heat transfer by conduction and natural convection on a heated vertical wall. Applied Thermal Engineering, Volume 29, Issues 2-3, February 2009, Pages 334-339.
[10] Blanco Ilzarbe, Jesús Mª; Sala Lizarraga, Jose Mª; López Gonzalez, Luis Mª.
Tecnología Energética. Publicacioes -Escuela Superior de Ingenieros. Bilbao, 2004.
ISBN: 84-95809-19-2.
[11] Karimipanah, Taghi. Building Energy Systems class notes. Lecture 1: Building Physics. Department of Technology and Built Environment. Fall 2013.
[12] Hsue-shen Tsien. Heat conduction across a Partilly Insulated Wall. Collected works of Tsien (1938-1956), 2012, Pages 227-230.
[13] Velle, Bjorn Petter; Hynd, Andrew; Gustavsen, Arild; Arasteh, Dariush; Goudey, Howdy; Hart, Robert. Fenestration of today and tomorrow: A state-of-the-art renew and future research opportunities. Solar Energy materials and Solar cells, Volume 96, January 2012, Pages 1-28.
[14] Herrero, M. Leire. Heat Balance of a historical church: solar heat gain. University of Gävle. 2014.
[15] Kent, R (1999): Composites and Plastics in Construction [online] Available from:
http://www.tangram.co.uk/TI-Polymer-Plastc&CompositeWindows.html [Accessed 20 May 2011]
[16] Norma Básica de la edificación “NBE-CT-79” sobre Condiciones Térmicas de los Edificios. REAL DECRETO 2429/1979, 6-JUL de la Presidencia del Gobierno. B.O.E.:
22-OCT-79.
[17] Pielichowska, Kinga and Krzysztof. Phase change materials for energy storage.
Progress in Materials Science, Volume 65, August 2014, Pages 67-123.
[18]http://www.wunderground.com/history/airport/ESOW/2013/9/23/MonthlyHistory.html
#calendar
[19] Helping you meet Part L of Government Building Regulations, Pilkington. Available from:
http://www.pilkington.com/~/media/Pilkington/Site%20Content/UK/Reference/TableofD efaultUValues.ashx
[20] Aristegui, Jesus. Heat Balance of a historical church: air infiltration losses.
University of Gävle. 2014.
[21] Petrucci, Ralph H.; Harwood, Williams S; Herring, F. Geoffrey. General Chemistry.
Prentice Hall. 8th edition. 2006. ISBN: 978-84-205-3533-3
[22] Swedish Energy Agency: Real energy prices for households in Sweden including energy taxes and VAT, 1986-2010 IN öre/kWh.
[23] Fernández, Inés; Martínez, Mónica; Segarra. M; Cabeza, Luisa F: Selection of materials with potential in thermal energy storage. Department of Materials Science &
Metallurgical Engineering, Universidad de Barcelona.
[24] Mardan, Nawzad. Industrial Energy Systems class notes. Lecture 2: Energy Technology. University of Gävle.
8 APPENDIX
8.1 Dimensions of the church
Figure 1 Appendix. Church’ top view
Figure 2 Appendix. Church’ lateral view
8.2 Data for heat loss calculation
Table 2. Data for heat loss through walls
TRANSMISSION LOSSES THROUGH WALLS
Total area 906,06 m2
Materials Stone and lime mortar (1,3m), plaster (0,001m)
Thermal parameters λstone=2,33[W/m K]; λplaster=0,3[W/m K]
U-value calculation Eq. (6)
U-value 1,3612 [W/m2 K]
Heat loss calculation formula Eq. (8)
Total area of the walls:
Atot=Along. + Aperp. – Awindows
Along. + Aperp. =[(40,18*9,9)+(16,64*9,9)]*2 = 1125.036 m2 Next the space occupied for a window has been obtained Awindows= Awindow1+ Awindow2+ Awindow3
Awindow1= [(2,61*3,29)+ (π* 2,012*0.5)]*12=179,196 m2 Awindow2= [(2,61*3,29*0,5)+ (π* 2,012*0.5)]*2=21,23 m2
Awindow3=[((3,29*0,5)-0,522)*2,61)+ (π* 2,012*0.5)]*2= 18,55 m2
Atot= 906,06 m2
U-value calculation:
UTot=1/RTot
RTot= RCOND+RCONV
RCONV=sum (1/h)= 1/hi+1/he=0,17 (m2/W K) [8]
Where hi and he are interior and exterior surface convection coefficient values.
RCOND=sum (di/λi) (m2/W K)
UTot=1/(0,17+(1,3/2,33)+2*(0,001/0,3))=1,3612 [W/m2 K]
Table 3. Data for heat loss through floor
TRANSMISSION LOSSES THROUGH FLOOR
Total area 668,59 m2
Materials Wood board (0,045m), lime sand (0,17m)
Thermal parameters λwood=2,33[W/m K]; λlime sand=0,3[W/m K]
U-value calculation Eq. (6)
U-value 0,9531 [W/m2 K]
Heat loss calculation formula Eq. (8)
Area of the floor:
A= (40,18*16,64)=668,6 m2 U-value calculation:
UTot=1/RTot
RTot= RCOND+RCONV
RCONV=sum (1/h)= 1/hi+1/he=0,22 (m2/W K) [8]
Where hi and he are interior and exterior surface convection coefficient values.
RCOND=sum (di/λi) (m2/W K)
UTot=1/(0,22+(0,17/0,87)+2*(0,045/0,142))=0,9531 [W/m2 K]
Table 4. Data for heat loss through windows
TRANSMISSION LOSSES THROUGH WINDOWS
Total area 88,75 m2
Materials Glass (0,015m), air gap (0,15m) wood frame
Thermal parameters λglass=0,78[W/m K]; λair=0,026[W/m K]
U-value calculation Eq. (6)
U-value [13] 2,8 [W/m2 K]
Heat loss calculation formula Eq. (8)
Helping you meet Part L of Government Building Regulations, Pilkington
Total area of windows:
It is important to mention that the window frame has been neglected. For the calculation of the area of one single window only glass has been taken into account.
Thus, and as the dimensions of separate glasses are provided, a multiplication has been done.
Awindow1=[30 glasses* (0,522*0,401)]*6*2(facade) Awindow2=[18 glasses*(0,522*0,401)]*2(facade) Awindow3=[14 glasses*(0,522*0,401)]*2(facade) Awindows=424 glasses (0,522*0,401)=88,75 m2
Next find attached the table where surface heat transfer coefficients have been taken from.
Figure 3 Appendix. 1/hi and 1/he values.” NBE-CT-79”
