UNDERFLOOR HEATING A solution or a problem?

Transcription

1 UNDERFLOOR HEATING A solution or a problem? Joakim Larsson Master Thesis in Energy-efficient and Environmental Buildings Faculty of Engineering Lund University

2 Lund University Lund University, with eight faculties and a number of research centers and specialized institutes, is the largest establishment for research and higher education in Scandinavia. The main part of the University is situated in the small city of Lund which has about inhabitants. A number of departments for research and education are, however, located in Malmö and Helsingborg. Lund University was founded in 1666 and has today a total staff of employees and students attending 280 degree programs and subject courses offered by 63 departments. Master Program in Energy-efficient and Environmental Building Design This international program provides knowledge, skills and competencies within the area of energy-efficient and environmental building design in cold climates. The goal is to train highly skilled professionals, who will significantly contribute to and influence the design, building or renovation of energy-efficient buildings, taking into consideration the architecture and environment, the inhabitants behavior and needs, their health and comfort as well as the overall economy. The degree project is the final part of the master program leading to a Master of Science (120 credits) in Energy-efficient and Environmental Buildings. Examiner: Hans Bagge (Building Physics) Supervisor: Dennis Johansson (HVAC) Keywords: Underfloor heating, Energy, Thermal mass, Energy efficiency, Heating systems Thesis: EEBD 15/10

3 Table of content Underfloor heating- a solution or a problem 1 Background Energy and environmental issues EU directives National targets Energy in Swedish residential buildings Underfloor heating Possible benefits of underfloor heating Possible disadvantages with underfloor heating Floor materials System control Underfloor heating in combination with heat pumps Objectives Limitations 4 2 Method Questionnaire study Indoor climate measurements Loggers and outdoor climate Sorting of values Analyses of the measured houses Simulations Industry knowledge and directives 9 3 Results and analysis Questionnaire study Overall satisfaction Discomforts During heating season During the whole year Flooring materials Cold floors Varying temperature with different flooring materials Wanted temperature 19

4 3.2 Indoor climate measurements Temperature measurements Distribution of logged temperatures Influence of the outside temperature Comparison between the two measured systems Humidity measurements Comparison between the two measured systems Influence of the outside relative humidity Analysing the measured residences Comparing with the questionnaire answers Moisture addition Simulations Energy simulations Thermal mass 40 4 Discussion Industry knowledge Questionnaire study Indoor climate measurements Simulations 46 5 Conclusions Future work References Appendix A Appendix B... 57

5 1 Background 1.1 Energy and environmental issues According to the Intergovernmental Panel on Climate Change, IPCC, it is clear that humans have had a grave impact on the climate changes that has taken place since the 1950s. The atmosphere and the oceans are getting warmer which causes ice and snow to melt, raises the sea-levels and increases the risk for natural disasters. The anthropogenic emissions of greenhouse gases are at an all-time high, much because of the persistent use of fossil fuels. 80% of the world s energy use still comes from fossil fuels. This might come as a surprise since the negative impact of using fossil fuel is well known and that the environmental question often is high on the political agenda. (IPCC,2013) There are several reasons for this, one being the exponential increase of human population, another is that although highly developed countries use of fossil fuel decreases the use in less developed countries increases as they are reaching for quick and cheap changes. Renewable energy sources, which have a much lower emission of greenhouse gases than fossil fuels, are becoming more evolved and more common. This is a step in the right direction, but it is not the only solution. In order to more effectively decrease the environmental impact the use of energy should be lowered EU directives In March 2007 the European Union leaders set new targets for its members in order to try reducing the environmental impact and to support the development of renewable energy sources. The three major objectives are; a 20% reduction in EU greenhouse gas emissions from 1990 levels, raising the share of EU energy consumption produced from renewable resources to 20 % and a 20% improvement in the EU s energy efficiency. Because of these three key objectives the targets are known as the targets and are aimed to be fulfilled in National targets The Effort Sharing Decision sets national targets for 2020 which is binding for each member in the European Union. This decision targets the 60% of greenhouse gas emissions that is not produced by the industrial sector and therefore not covered by the EU Emission Trading System. The targets which is expressed in percentage-change from 2005s levels is decided by the wealth of each country, this means that a wealthy country have to lower its emissions more than a less wealthy. A less wealthy country is even allowed to increase their percentage in order to leave space for a growing economy, the main goal is that in 2020 the greenhouse gas emissions (covered by the Effort Sharing Decision) from all members of the European Union should be lowered by 10% Energy in Swedish residential buildings As set by the Effort Sharing Decision Sweden needs to lower its greenhouse emissions outside the industrial sector with 17% compared to 2005s levels. Greenhouse gases from residential buildings fall under this category and will be addressed by improving the energy performance of buildings. (Council of European Union, 2015) 1

6 In 2013 the energy consumed within residential buildings in Sweden was GWh and approximately 87% (55181 GWh) of this energy was used to heat the buildings. A good way to reduce the consumption of energy and thereby lower the impact on the environment could be to use more efficient heating methods. (Statistikcentralen, 2014) 1.2 Underfloor heating Underfloor heating is often promoted to be an energy efficient heating method and is becoming more and more common in Swedish single family houses. 61% of all single family houses built in Sweden during was equipped with underfloor heating, which is a large increase compared to where only 10% of new buildings where equipped. (Betsi, 2009) An underfloor heating system functions similar to the traditional radiator heating system, but instead of having hot water running through and heating small surfaces, such as radiators that are placed inside the room, the hot water runs through pipes that are casted in the foundation under the floor or placed underneath the flooring material and therefore heats up the larger floor area. According to the Swedish authorities the floor surface should not exceed 27 C. (T2, 2002) Possible benefits of underfloor heating Underfloor heating should take away the factor of cold floors which is a desirable advantage for many. It is also hidden underneath the flooring and does not take away space or affect the appearance of the living area. The human head thrives in a temperature of about C but the feet wants a temperature about 5 C higher than that. If a room is heated from the floor the general temperature in the room should thereby be able to be lower, because the human feet is the primary sensory organs for temperature i.e. if the feet are warm we feel warm. This should, according to experts, allow for a room temperature that is 2-3 C lower and an energy saving of about 15% than if a conventional radiator system were used. (Boverket, 2015) Since radiators are relatively small in area the water needs to be relatively hot in order to heat an entire room, the radiated heat will also mostly be located around the radiator. This should not be the case for underfloor heating. Since the entire floor is heated there is a lot of contact between the heated floor and the air, which should allow for lower water temperatures in the system and more dispersed heat in the entire room. (Boverket, 2015) Utilizing the thermal storage in a building is often a good way to lower the amount of energy needed to keep a building heated. Since the entire floor is heated when underfloor heating systems are used there is a lot of mass where the thermal energy can be stored. This stored energy should help to keep a uniform indoor temperature throughout the day and lower the energy need Possible disadvantages with underfloor heating Floor heating systems radiates the same amount of heat up to the building as it does down to the foundation, it is therefore important to have a lot of insulation in the foundation to prevent the energy from being wasted in to the ground. According to Swedish authorities and experts it is recommended to have at least 250 millimetres of insulation below the floor 2

7 heating system. This will lead to a higher initial cost of the system and can be hard to implement when renovating or rebuilding. (Boverket, 2015) It is also debatable that since such a large surface is heated by the system it is not to recommend if the demand of energy is low. It will always take a certain amount of energy to heat this large surface, which leads to that the minimum amount of energy that can be provided by an underfloor heating system is higher than systems that uses smaller surfaces. If the system is used in a well-insulated building with an energy demand that is lower than the minimum energy that can be provided, the system may turn on and off and thereby provide uneven temperatures and waste energy. This can make the underfloor heating system difficult in new buildings where it is common to have a lot of insulation in order to reach the energy goals. Since it is common to have the floor heating casted inside the concrete, which can store a lot of heat, there will be a time delay before any changes of heat supply will influence the temperature of the room. This means that if the temperature outdoor rapidly changes it will take time before the heating system adapts, which can lead to both overheated and cold indoor climate. If the building has large windows and a slowly adapted heating system, solar energy in combination with the stored energy in the concrete can rapidly increase the indoor temperature and lead to uneven temperatures and overheating. It is common to place radiators underneath windows to avoid downdraughts from the cold window surfaces, which is not possible with an under floor heating system. To avoid this complication the Swedish authorities and experts recommend that window constructions with a U-value below 1.0 W/(m²K) are installed. These window constructions are expensive and this will raise the price of installing underfloor heating both in new buildings and renovations. (Boverket, 2015) It can also be argued that there is an increased risk of water damage with a floor heating system compared with other heating systems. If there is a leak in any of the water pipes in the floor it would be hard to detect in time and the water damage it causes could be very extensive. A discussion with Vattenskadecentrum (Water damage center) revealed no known, apparent increase of such risks Floor materials The type of flooring material chosen when using an underfloor heating system can have a high impact on how the system works. If a heavy material, such as stone that stores a lot of heat, is chosen it should create a system that takes a relatively long time to influence the temperature in the room. When the outdoor temperature quickly drops this can help to keep an even indoor temperature, but when the outdoor temperature quickly raises or the sun starts to shine the combined energies could create overheating since the heating system is slow to adapt. If a lighter material, such as parquet floor, that does not store so much heat, is chosen the heating system should be quicker to adapt to changing conditions. If the outdoor temperature then quickly raises or the sun starts shining the flooring material does not have a lot of energy stored and will faster adapt. The same goes for if the temperature outside rapidly drops. 3

8 1.2.4 System control Underfloor heating- a solution or a problem There are different ways on how the underfloor heating can be controlled. The standard being a thermostat either in the floor or in the room, this could create problems since heat from other sources is not taken under consideration. There is a more energy efficient way where the thermostat measures the temperature both in the floor and in the room at the same time and thereby utilizes heat from other sources such as the sun or people. (T2, 2002) Underfloor heating in combination with heat pumps A heat pump can be used in combinations with an underfloor heating system. The efficiency of the heat pump is called the Coefficient of Performance (COP) and is the ratio between the energy usage of the compressor and amount of useful heat extracted from the condenser. The COP for a heat pump is affected by several factors, one being the temperature difference between the heat distribution and the heat source. The lower this temperature lift is the higher the COP of the heat pump will be. See Figure 1.1 for example. (Berntsson, 2000) Figure 1.1 COP difference with different temperature lifts with different types of heat pumps Since an underfloor heating system operates with a lower temperature than for example a radiator heating system the temperature lift will be lower when using this system, giving the heat pump a higher COP. If a heat pump is used in combination with a heating system it is therefore more beneficial to use an underfloor heating system. 1.3 Objectives Underfloor heating has both advantages and disadvantages in different perspectives regarding energy use, indoor climate and economy. Particularly the option to utilize the thermal mass is influence with an underfloor heating system. This thesis will investigate the existing knowledge on issue of underfloor heating and how residents with underfloor heating perceive their indoor climate by a questionnaire. It will also include indoor climate measurements and energy simulations to try to resolve important factors influencing the energy use and indoor climate by use of underfloor heating. 1.4 Limitations Variation of COP for different heat pumps with temperature lift LIFT ( C) TYPE OF HEAT PUMP 20 C 25 C 30 C 35 C 40 C 45 C 50 C 55 C 60 C Earth source (G & W) High efficiency ASHP Standard ASHP This thesis has limited its research to single family houses and thereby taking away the factor of heating from others dwellings. Electric floor heating is not investigated in this study, since it is considered having to high primary energy use to be worthwhile. The underfloor heating system is only looked at as a heating system in this thesis and not as a cooling system where cold water is run through instead of hot water. 4

9 Measurements and simulations made in this study are limited to two heating systems, water radiator heating systems and water underfloor heating systems. Results from simulations are based on the geographical location Helsingborg in Sweden and any conclusions based on these results may not be representative for different locations. 5

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11 2 Method Underfloor heating- a solution or a problem In this chapter the different methods used in order to fulfil the objectives of this thesis is presented. 2.1 Questionnaire study In order to determine how pleased residents are and how they perceive their indoor climate with underfloor heating it was decided that a questionnaire study needed to be conducted. In order to get sensible results the single family houses targeted in the study needs to fulfil different requirements. The houses could not be too old since underfloor heating is rarer in older buildings and building standards have changed. Row houses and multiple family houses should be avoided because of the heat transfer between apartments or houses. If possible the targeted houses should have the same outdoor climate and thereby be affected by climate changes in the same way. It would also be preferred if the houses had different types of heating system in order to compare the results. It was, because of previous mentioned reasons, decided that to hand out paper questionnaires directly to the houses would be the most efficient way to carry out the study. By doing it this way, houses that did not meet the requirements could be skipped and only information valuable to the study would be collected. A relatively new built residential area with a lot of single family houses would fit well, both because of logistic reasons and that the houses would share the same outdoor climate. The questionnaires were delivered with a pre-stamped envelope and a covering letter (see Appendix A) that explains how and why the study is conducted. The questionnaire used is a composition between two surveys made by Boverket (small houses and adult) and a series of made up questions that were relevant to this thesis. In order to not reveal that the study is about underfloor heating or heating systems, which could affect the residents answers, the headline of the questionnaire was A few questions about your indoor climate and also contains some questions that are not relevant to the study. In the survey (which can be seen in appendix B in Swedish) the residents answers questions on a scale from either 1-5 or 1-3 on how pleased they are with aspects of their indoor climate regarding different phenomenon, changing outdoor climate etc. The questionnaire also contains questions about which types of flooring material the house has and which types of heating systems that exists. The respondents will be able to remain anonymous or will be able to fill in their name and phone number and thereby accepting further questioning if needed. The results from the questionnaire study will be analysed and answers from houses with different heating systems will be compared, the level of satisfaction with underfloor heating in different aspects will try to be determined and the most common floor materials will affect the upcoming simulations in this thesis. Maria Park, a residential area located a few kilometres north of Helsingborg in Sweden, was chosen to be the target area of this study. It was chosen because it is a large residential area (which means a lot of potential respondents), it is relatively new built and has a lot of single family houses that does not have the same type of heating systems. 7

12 A total of 400 surveys were handed out directly to the mailbox of houses in Maria Park. They were only handed out to buildings that looked to fit the requirements, houses that did not were skipped. 2.2 Indoor climate measurements In order to get a more detailed view of how the indoor climate changes with different factors, it was decided that temperature and humidity measurements needs to be made on single family houses with water underfloor heating systems and the more traditional water radiator heating systems. Respondents from the questionnaire study with these types of heating systems will be selected and asked if they allow for measuring in their homes. The selected responders should meet the requirements mentioned in chapter 2.1. They should especially share the same outdoor climate in order to be able to be compared with each other. The purpose of doing these measurements will be to try to see how and how fast the two different systems adapts to changes in the outdoor climate, if the indoor temperature varies more with one system compared to the other and if the average temperature with an underfloor heating system is lower than with a radiator heating system. In order to collect data when the outdoor climate creates interesting conditions and to be sure that the heating systems would be turned on, the measuring period for all measured houses was set to be between the 20 th March and the 10 th of April (during the heating season) Loggers and outdoor climate The loggers used in the measuring was Onset HOBO temp/rh loggers which has a margin of error of ±0.21 C for temperature and a 2.5% accuracy for relative humidity. Since ±0.21 C does not make a significant difference in these measurements it was discussed and decided that this should be ignored. The relative humidity was on the other hand corrected since 2.5% makes a significant difference in the range of the data that was collected. The logger registered values every fifth minute for both temperature and relative humidity. (Onset, 2015) The residents were instructed not to place the logger in direct sun light, on the floor or in a box or cabinet. It was recommended to place the logger in the hall or living room where the humidity from the kitchen or the bathroom affected as little as possible. Data for the outdoor climate was taken from SMHI s measurements of Helsingborg for the time of interest. SMHI s temperature and relative humidity measurements were given, unlike the loggers, for every hour. (SMHI, 2015) Sorting of values Microsoft Excel was used to sort and analyse the measurements, all values was scanned in order to detect unrealistic values that could have been caused by residents moving the loggers. No such values were detected. Since the measurements from SMHI was given every hour and the measurements from the loggers every fifth minute the values did not enter the same rows in excel. This was problematic because diagrams that include both measurements, in order to analyse the 8

13 results, were required. A macro was written in excel to insert eleven empty rows between every value given from SMHI and thereby matching the loggers values. The macro can be seen in Figure 2.1. Figure 2.1 Macro used to insert eleven empty rows between every value in Excel Analyses of the measured houses In order to see how well the residents perceive their indoor climate, the answers of the questionnaire study (for the measured houses) were compared with the measured data. To give a clearer view on how the buildings are used, moisture supply were calculated for each measured residences. 2.3 Simulations Many of the possible advantages and disadvantages of having underfloor heating systems comes from the fact that the system heats up a large area and then uses this stored energy to create an even indoor climate throughout the day. It is also alleged that an underfloor heating system allows for a lower room temperature and because of that needs less energy. To try to determine if the possible advantages and disadvantages with an underfloor heating system, which is more explained in chapter and 1.2.2, is correct a series of simulations will be made using Design Builder, which is an interface program for EnergyPlus. The simulated building in this study will be a 16 m times 12 m one story single family house. Two different heating systems will be used, water underfloor system and water radiator system. Different flooring materials will be used based on the results from the questionnaire study and different U-values on building components will be used in order to try to see how this affects the energy consumption and balance of the systems. 2.4 Industry knowledge and directives To be able to determine the possible advantages and disadvantages of using an underfloor heating system and try to investigate the ones that cannot be investigated through simulations, a literature study and interviews with expert and authorities will be conducted. This study will also aim to find out the level of knowledge and what types of guidelines that exist in the building industry. The possible advantages and disadvantages found through this study are described in chapter and the conclusions of this study will be discussed in chapter 4. 9

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15 3 Results and analysis Underfloor heating- a solution or a problem In this chapter the results from the different studies are presented and analysed. Some discoveries and interesting results are pointed out and shortly commented but will be more discussed in chapter Questionnaire study Off the 400 residents asked 141 responded, which is an answering rate of approximately 35%, most of them responding anonymously. 120 residences used underfloor heating and 21 used other heating systems. The results of these 141 answered questionnaires were compared and analysed using Microsoft Excel. In order to compare underfloor heating systems (shortened UFH) with other systems, answered questionnaires with underfloor heating was sorted out, these results was then compared with results from answered questionnaires with different heating system (which is referred to in this thesis as other ). In order to analyse the results, an average of the answers is calculated and the percentile for 97.5% and 2.5% are used to see the spread of the answers. The percentile is a measure that indicates the value where the given percentage of observations in a group of observations is below, for example if the 97.5 percentile is 20, 97.5% of all values are below Overall satisfaction The respondents have answered questions on how satisfied or dissatisfied they are with their residence on a scale from 1-5, 1 being satisfied and 5 being dissatisfied. Underfloor heating systems are compared with other heating systems in order to try to see if this system is more satisfying. 11

16 5 4 3 Percentile 97.5 Average Percentile How satisfied are you with your residence as a whole? (UFH) How satisfied are you with your residence as a whole? (Other) How satisfied are you with your residence regarding energy use? (UFH) How satisfied are you with your residence regarding energy use? (Other) How satisfied are you with the thermal comfort in your residence? (UFH) How satisfied are you with the thermal comfort in your residence? (Other) Figure 3.1 Results from the overall satisfaction questions in the survey. The higher the number on the x- axis is the more dissatisfied the responders are. In all questions seen in Figure 3.1 residences with underfloor heating is on average slightly more satisfying than residences that use other heating systems. The spread in the answers are however greater with underfloor heating system, this shows that responders that are dissatisfied with energy use and thermal comfort of their residence are more dissatisfied if they have an underfloor heating system. This is particularly evident regarding energy use. High energy use on an underfloor heating system could indicate that the heat is wasted, either by lack of insulation or by factors that forces the system to turn on and off in order to keep the wanted indoor temperature. It could also mean that the residences with underfloor heating systems do not have a lower indoor temperature than residences with other heating methods Discomforts The respondents answered questions on how often they experience different discomforts such as draught or unsatisfying indoor temperatures. Answers were given on a scale from 1-3, 3 being never, 2 being sometimes and 1 being often. The goal of these questions was to try to see if different discomforts are more common or less common when using an underfloor heating system and try to see if it is harder to control these types of systems. 12

17 During heating season Underfloor heating- a solution or a problem Since the heating systems is mostly used during the heating season and since interesting conditions are in place during this time some questions are asked only for this time frame. The interesting conditions being that the solar energy is affecting the indoor climate even though it is still cold outside. On the x-axis 3 means never, 2 means sometimes and 1 means often Have you during the last 3 month (dec-feb) been troubled by Percentile 97.5 Average Percentile 2.5 Figure 3.2 Results of discomfort factors during the heating season As seen in Figure 3.2 underfloor heating systems do not differ much from other systems regarding discomfort during heating season. Interesting is that when the respondent have problems with varying room temperatures they have more problem with underfloor heating systems than other systems even though the average is better. Draught does not appear to be more problematic in houses with underfloor heating and it is more common with high temperatures when using other systems During the whole year The respondents were then asked if and how frequent discomforting temperatures occur in their residence during the summer and the winter. 13

18 4 Are you in your residence troubled by Percentile 97.5 Average 1 Percentile Figure 3.3 Survey results of discomforting indoor temperatures during summer and winter The respondents view on discomforting temperatures during summer or winter in their residence is almost the same whether they have an underfloor heating system or not (as seen in Figure 3.3). The only difference is that underfloor heating systems have a slightly better average when it comes to uncomfortable cold temperatures during winter time. Highest discomfort is with high temperatures during summer time. The responders were asked if and how often different types of draught occurred in their residence and if and how often they experience cold floors. This is interesting since underfloor heating systems does not prevent downdraught in the same way as for example radiator heating systems Are you in your residence troubled by Percentile 97.5 Average Percentile 2.5 Figure 3.4 Survey results on frequency of different discomforting factors 14

19 As seen in Figure 3.4 downdraught from windows does not occur especially often in residence with underfloor heating systems, which could be a possible disadvantage of using this system, although it is more common than when using other systems. Another interesting result is that cold floors is nearly as common in underfloor heating systems as it is in other systems even though the heat radiates from the floor. To try to see if underfloor heating systems are harder to control than other systems and if the temperature varies during changes in the outdoor temperature, the respondents answered questions on how they perceive these issues. 4 Are you in your residence troubled by Percentile Average 0 varying room temperatures during temperature changes outside (UFH) varying room temperatures during temperature changes outside (other) difficulty to influence room temperature (UFH) difficulty to influence room temperature (other) Percentile 2.5 Figure 3.5 Results on how respondents perceive varying room temperatures and difficulty to influence the this temperature As seen in Figure 3.5 it is more common to have varying room temperature during temperature changes outside when using an underfloor heating system. This indicates that this system is slow to adapt to changing conditions. When the respondents have difficulty to influence the room temperature they have a higher level of difficulty if they use an underfloor heating system. Despite that it is more common to have a problem with this if another system is used Flooring materials To see which flooring material that is the most common when using underfloor heating systems, the respondents answered questions on which types of flooring materials they have, both on the ground floor and upstairs floors. It is also of interest to see if the designers of the buildings prefer to use a flooring material that stores much heat or a material that stores lower amounts of heat. These results are presented in percent of how many of the residences that have a specific type of flooring material above an underfloor heating system. 15

20 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 2.5% PVC-/vinyl floor 84.2% 85.8% Wood/wood parquet Tiled 9.2% Stone Figure 3.6 Results in percentage on how common certain flooring materials above underfloor heating is on the ground floor 100% 90% 80% 70% 70.0% 60% 50% 40% 30% 20% 14.2% 20.8% 10% 0% 0.8% Carpeted Wood/wood parquet 1.7% Tiled Stone No underfloor heating upstairs Figure 3.7 Results in percentage on how common certain flooring materials above underfloor heating is on upstairs floors From the results that is presented in Figure 3.6 and Figure 3.7 it is clear that wooden flooring and tiled flooring, often in combination (which is the reason the percent s adds up to more than 100), is the most common flooring material when using underfloor heating systems. These two flooring materials will therefore be used and analysed in the upcoming simulations. It is approximately equally common with tiled as it is with wooden flooring and therefore the results do not answer if a heavy flooring material is more preferred than a lighter. The results also show that 70% of all respondents with underfloor heating systems do not have underfloor heating systems on the upstairs floors. This can be explained by that it takes a lot of labour to put in all the piping to have an underfloor heating system on upstairs floors, which in turn can cost more than it gives. 16

21 Cold floors Underfloor heating- a solution or a problem According to the survey residents with underfloor heating systems experience cold floors nearly as much as residents without this system, which is peculiar since the heat is supplied from the floor. In order to try to find a reason for this the surveys where cold floors were a discomfort was sorted out to see which flooring material these houses have. 3.0% 87.9% 90.9% Wood/wood parquet Tiled Stone Figure 3.8 Flooring materials when having discomfort with cold floors and using an underfloor heating system As seen in Figure 3.8 it is most common to have a combination of tiled flooring and wooden flooring. 82% of the houses in this study have that combination above their underfloor heating system. It is therefore hard to be sure if one material causes cold floors more than the other. It is only residents with these three flooring materials that have problems with cold floors Varying temperature with different flooring materials As explained in chapter the flooring material can have an impact on how much the indoor temperature varies with an underfloor heating system. In order to try to see if the flooring material influences the varying indoor temperature, the respondents with this issue was sorted out and the flooring materials of this residences was compared. This is done to see if it is more or less common with varying indoor temperature with a lighter of heavier flooring material. 17

22 9.9% 85.6% 82.9% Wood/wood parquet PVC-/vinyl floor Tiled Stone 2.7% Figure 3.9 Flooring material when having problems with varying indoor temperature caused by changing outdoor temperature As seen in Figure 3.9 it is slightly more common to have a heavy flooring material when having problems with varying indoor temperature, the difference is although very small. In order to investigate this further, only residence that often has problems with varying temperature (answer 3) is sorted out and their flooring materials are compared. 13.6% 84.1% 75.0% Wood/wood parquet PVC-/vinyl floor Tiled Stone 2.3% Figure 3.10 Flooring material when often having problems with varying indoor temperature caused by changing outdoor temperature In Figure 3.10 the difference is clearer, it is more common with heavy flooring materials when often having problem with varying indoor temperature caused by changing temperature outdoors. 18

23 3.1.4 Wanted temperature Underfloor heating- a solution or a problem In the survey the respondents answered on which temperature they would like to have in their residence and which temperature they experience, both for winter and summer. The average difference between these temperatures would give a result on how close the heating system is on giving the wanted temperatures, at least how close the respondents perceive it to be. Temperature difference/ C Winter (UFH) Summer (UFH) Winter (other) Summer (other) Percentile 97.5 Average Percentile 2.5 Figure 3.11 Results on the difference between wanted and perceived indoor temperature in winter and summer As seen in Figure 3.11 the difference in wanted and perceived indoor temperature is very low during winter time. In summer the difference is, in both underfloor heating and other systems, much larger but more when using underfloor heating. Some of the respondents using this system could even perceive temperatures more than 9 C warmer than what they would like to have. 3.2 Indoor climate measurements In the questionnaire study the respondents could leave their name and telephone number and accept to be contacted if needed. Some respondents did that and a few of them was contacted and asked if they would allow temperature and humidity measuring in their residence. Three residences with water radiator systems and four residences with water underfloor heating systems allowed measuring. 19

24 3.2.1 Temperature measurements One of the possible advantages of underfloor heating is that it should allow a lower indoor temperature than for example radiator heating systems. In order to see if this is correct, in the measurements made for this study, an average of all logged temperatures in each residence was calculated and compared. Figure 3.12 Results of the average temperatures of the measured residences As seen in Figure 3.12 only Underfloor heating 2 has a significantly lower average temperature than the residences using radiators. In the other residences the average temperature is fairly even. The percentiles give an indication that the spread of logged temperatures is larger in the residences that uses underfloor heating systems Distribution of logged temperatures To take a closer look on the spread and to some extent see how much the indoor temperature varies, the logged temperatures were sorted from smallest to largest and then compared. 20

25 Temperature/ C Temperature/ C Radiator 1 Radiator 2 Radiator 3 Underfloor heating 1 Underfloor heating 2 Underfloor heating 3 Underfloor heating 4 Outdoors (second axis) Figure 3.13 Variation in temperature for the measured residences In Figure 3.13 it can be seen that the radiator systems (the line of Radiator 1 is underneath the line of Radiator 2) has a spread that is more even than the underfloor heating systems. The temperature in all residences seems to more or less follow the curve of the outdoor temperature. The underfloor heating systems have more thermal spikes, which could indicate that these systems are slower to adapt to raising outdoor temperatures or solar gains. To try to see how fast the heating system in each residence adapted to changing outdoor temperatures, the measured indoor temperature was compared with the outdoor temperature. Looking for heat peaks indoors and if they occur shortly after raising temperatures outside, also to try to see how high these peaks gets. In figure this comparison is presented for each residence. Temperature/ C Temperature/ C Inside Temp Outside Temp /03/ :00 29/03/ :00 08/04/ :00-10 Figure 3.14 Inside temperature for Radiator 1 compared with the outside temperature 21

26 Temperature/ C Temperature/ C Inside temp Outside Temp /03/ :00 29/03/ :00 08/04/ :00-10 Figure 3.15 Inside temperature for Radiator 2 compared with the outside temperature Temperature/ C Temperature/ C /03/ :00 29/03/ :00 08/04/ :00 Inside Temp Outside Temp Figure 3.16 Inside temperature for Radiator 3 compared with the outside temperature Temperature/ C Temperature/ C /03/ :00 29/03/ :00 08/04/ :00 Inside Temp Outside temp Figure 3.17 Inside temperature for Underfloor heating 1 compared with the outside temperature 22

27 Temperature/ C Temperature/ C Inside Temp Outside Temp 18 19/03/ :00 29/03/ :00 08/04/ :00-10 Figure 3.18 Inside temperature for Underfloor heating 2 compared with the outside temperature Temperature/ C Temperature/ C /03/ :00 29/03/ :00 08/04/ : Inside Temp Outside Temp Figure 3.19 Inside temperature for Underfloor heating 3 compared with the outside temperature Temperature/ C Temperature/ C Inside Temp Outside Temp 19 19/03/ :00 29/03/ :00 08/04/ :00-10 Figure 3.20 Inside temperature for Underfloor heating 4 compared with the outside temperature 23

28 It is no surprise that the temperature raises shortly after raising temperatures outside, the interesting, with the comparisons in Figure 3.14-Figure 3.20, is to see how fast the system adjusts its heating after these heat peaks outside. After examining these diagrams and the data behind them it seems that the underfloor heating systems is slower to adapt and therefore causes higher temperature peaks than radiator systems. To more see how the temperature differs inside the measured residences the difference between the maximum and the minimum temperature in each residence was calculated. Table 3.1 The temperature difference between the maximum and the minimum temperature for every measured day in the measured residences Date UFH1/ C UFH2/ C UFH3/ C UFH4/ C Rad1/ C Rad2/ C Rad3/ C 20/03/ /03/ /03/ /03/ /03/ /03/ /03/ /03/ /03/ /03/ /03/ /03/ /04/ /04/ /04/ /04/ /04/ /04/ /04/ /04/ /04/ Average:

29 As seen in Table 3.1 it is more common to a have larger temperature difference between the daily maximum and minimum indoor temperatures when using an underfloor heating system. When examining Figure 3.18 it looks like Underfloor heating 2 should have a less varying indoor temperature than the rest of the residences but it has a peak on the third of April that affects its average in Table 3.1. If this date was to be taken away the average daily temperature difference would be 1.13 C, which is as good as for a residences using radiator heating Influence of the outside temperature In order to closer investigate how much the outside temperature influences the inside temperature, diagrams with the indoor temperature as a function of the outside temperature were made. With the help of Excel a trend line and an equation that shows the connection between the two variables were added. Temperature/ C y = x R² = Temperature/ C Figure 3.21 The inside temperature as a function of the outside temperature in Underfloor heating 1 As seen in Figure 3.21 there is, unsurprisingly, a connection between the outdoor and indoor temperature. The interesting being the factor in front of x (for future references called k) in the equation, the closer this factor k is to one the larger the connection is between the outside and inside temperature. The coefficient of determination (R²) describes how well one variable describes the other, in this case how well the outdoor temperature describes the indoor. If R² is between minus one and zero the connection is negative, if it is zero there is no connection and if it is between zero and one the connection is positive. This analysis was made for all measured residences and the resulting coefficients are presented in the table below. 25

30 Table 3.2 The connection variables for the indoor and outdoor temperatures in the measured residences k R² Average k Underfloor heating Average R² Underfloor heating Underfloor heating Underfloor heating Radiator Radiator Radiator It seems like the outdoor temperature has a slightly larger influence on the indoor temperature when using underfloor heating systems. The average coefficients k and R² are larger for the residences with underfloor heating systems Comparison between the two measured systems In order to see how the two different systems compare with each other, interesting values such as average temperature, maximum and minimum temperature, for the measured temperatures of all residences with underfloor heating was compared with the values of all residences with radiator heating systems. Table 3.3 Temperature comparisons between the two systems Underfloor heating Radiators Average temperature/ C Standard deviation/ C Maximum temperature/ C Percentile 95/ C Percentile 75/ C Percentile 50/ C Percentile 25/ C Percentile 5/ C Minimum temperature/ C The standard deviation is a distribution measurement on how the values are distributed around the average value. As seen in Table 3.3 the average temperature is lower in the residences with underfloor heating but the standard deviations is larger, which indicates that temperatures when using this system varies more. 26

31 3.2.2 Humidity measurements Underfloor heating- a solution or a problem In order to see if there is any differences in humidity levels when using underfloor heating systems or radiator heating systems the same comparisons made with temperature in chapter was made for the measured humidity. Relative humidity/% percentile Average 2.5 percentile Radiator 1 Radiator 2 Radiator 3 Underfloor heating 1 Underfloor heating 2 Underfloor heating 3 Underfloor heating 4 Figure 3.22 Results of the average relative humidity in the measured residences In Figure 3.22 it is showed that there is no significant difference in the average relative humidity levels when using underfloor or radiator heating systems. The spread of the levels differs a lot from residence to residence and will therefore be further investigated. To try to see if there is more spread in relative humidity levels with the different heating systems, the measured values was sorted from smallest to largest and then compared. 27

32 Relative humidity/% 60 Underfloor heating- a solution or a problem Relative humidity/% 100 Radiator Radiator 2 Radiator3 Underfloor heating 1 Underfloor heating 2 Underfloor heating 3 Underfloor heating 4 Outside (second axis) Figure 3.23 Variation in relative humidity for the measured residences Figure 3.23 show that the residences using radiator heating systems have more high values of relative humidity, the residences with underfloor heating have more even relative humidity levels. To try to see how the relative humidity changes with the indoor temperature, these values were compared and analysed. This should give an indication of when the high level of relative humidity occurs. Temperature/ C 25.5 Relative humidity/% /03/ :00 29/03/ :00 08/04/ : Indoor temp Indoor RH Figure 3.24 Indoor relative humidity for Radiator 1 compared with the indoor temperature 28

33 Temperature/ C Relative humidity/% Indoor temp Indoor RH /03/ :00 29/03/ :00 08/04/ :00 20 Figure 3.25 Indoor relative humidity for Radiator 2 compared with the indoor temperature Temperature/ C Relative humidity/% /03/ :00 29/03/ :00 08/04/ :00 Indoor temp Indoor RH Figure 3.26 Indoor relative humidity for Radiator 3 compared with the indoor temperature Temperature/ C Relative humidity/% /03/ :00 29/03/ :00 08/04/ :00 Indoor temp Indoor RH Figure 3.27 Indoor relative humidity for Underfloor heating 1 compared with the indoor temperature 29