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Energy use and comfort, comparison of Bungalows in Spain.
Why not better than developed countries?
by Hakan Falk at Energy Saving Now. (energysavingnow.com)
Introduction.
I have had houses in Spain for 25 years and experienced the level of comfort in buildings in many geographical areas. 1997 I got involved in an investigation about introducing prefabricated Nordic houses in Spain. This was a study regarding use of prefabricated Nordic construction, for use as rental accommodation, compared to traditional construction in Spain. In the study I did calculations and comparisons between Nordic houses and traditional Spanish constructions. Some of the findings have almost a general worldwide validity and when I went trough some of my material, I decided to publish parts of it. It is especially interesting in the light of the EU commissions suggestions of using the Danish Building Code as a model for EU.
During the years and especially since I moved to Spain, my interest for the Spanish situation increased. I noticed that the construction methods and installation designs largely resulted in very over dimensioned systems for heating and air conditioning. Spain is wasting a very large amount of energy resources in its buildings and could save enormously by introducing better knowledge and standards. Spain is at the end of its biggest building boom in history and still do not have a country wide Thermal Building Code. The future implications of this, when the world will have more serious energy crises, can be immense.
The project with Spanish bungalows is interesting, because it is a product comparison and it at the same time highlights a general worldwide situation. The following will discuss the different factors that effect comfort and energy in traditional Spanish and Nordic constructions.
Description of simulation method.
I have used a Swedish computer program called BRIS which in English means BREEZE, by its original developers, professor and tech. Dr. Gösta Brown and tech. Dr. Engelbrekt Isfält, both at the Royal Technical University of Stockholm (KTH), with the help of program developer fil. Kand. Axel Bring who did the first versions. In 1972 Theodor Rosenthal rewrote the program from a special programming language to Fortran, with some assistance of myself, and have since then maintained and developed BREEZE. The first versions of the simulation program for energy transmission in building constructions existed already 1963 and it is still is one of the most advanced simulation programs in the world.
When the developers were presented with a Swedish energy price 1990, it was calculated that the use of BREEZE for design of buildings and research was saving energy in the range of 100's of millions yearly for the Swedish society. This sum is much larger today, since the new 1978 Thermal Building Codes was developed by the help of simulations with BREEZE. Since Sweden has no own oil resources, the impact of BREEZE is significant on the Swedish national economy.
In the following paragraphs is a description of factors that influence comfort and energy and how the BREEZE program takes consideration to them,
- The Construction.
BREEZE take in consideration the energy transmission through the construction, with correct transmission calculations. It also calculates energy storage and emission and the effect of those. One very important difference compared with other programs, is that HVAC systems are built into and coupled to the simulation model. Experiences has proved that the latter is absolutely necessary for a correct simulation.
- Climate.
The BREEZE simulation works with weather conditions and can do simulations with actual hourly weather conditions for up to one year. It also considers the effects of sun radiation at the specified site and will simulate the effects of sun radiation on facades and through windows, as well as give the indoor temperatures, surface temperature and indicators for comfort levels.
- Temperatures.
At the time of the calculations I had no access to meteorological data in Spain and the calculations are therefore performed with average temperatures ± amplitude. This will result in some discrepancies in comparison to real situation, but will still produce a correct comparison between the different construction types and results close to the realities. The following average temperatures was used,
| Month | Average Temperature | ± Amplitude |
| January | 4° | 6° |
| February | 6° | 6° |
| March | 8° | 6° |
| April | 12° | 6° |
| May | 16° | 6° |
| June | 20° | 6° |
| July | 24° | 6° |
| August | 28° | 6° |
| September | 24° | 6° |
| October | 18° | 6° |
| November | 12° | 6° |
| December | 8° | 6° |
These temperatures are estimated being relatively close to averages. experienced 50 km off the coast in Northern Catalonia.
- Sun radiation.
The BREEZE simulation will take in consideration the effects of sun radiation on facades and through windows at the location specified by longitude and latitude. In addition cloud cover and shadows can be considered. For the purpose of the comparisons, we did not consider any shadows, since they are location dependent and most calculations are for sunny days. The longitude and latitude were specified for the Barcelona/Girona area.
- Factors influencing the feeling of comfort.
A person will feel comfortable when it does not feel cold or hot and can maintain its body temperature with ease, The comfort is influenced by a number of environmental factors which includes,
Air temperature
Radiation exchange with hot and cold surfaces
Air movements
Humidity
Symmetry
The person is also a part of his environment and produces energy corresponding to the above factors. In total a person produces approx. 80 watt of energy without working and more if exercise is performed. The energy is divided as follows,
Radiation 50%
Convection 24%
Transpiration 22%
Lungs etc. 4%
The BREEZE simulation will handle the factors that are construction dependent such as the air temperature, surface temperatures, emission and symmetry. I will in the following describe each factor that influences comfort and its importance.
- Air temperature.
Because air temperature is easy to measure it is often wrongly used as a general measurement of comfort. It is also very often a large difference between the measured temperature and the temperature perceived by people. The perceived temperature is a combination of the earlier mentioned comfort factors. Air temperature can often compensate variations in radiation, air movements or humidity, i.e. during a sunny, cold and dry spring day, the temperature in the sun can be perceived as more than 20 degrees even if the air temperature is maybe 8-10 degree lower. The BREEZE simulation considers influence from radiation and calculates the perceived temperature, which is called effective temperature and people will mostly have a feeling of comfort with perceived temperatures between 18º to 20º C for heating and 22º to 24º for cooling. The values have been well verified in research by KTH in Stockholm.
- Radiation to and from surfaces.
A person will feel radiation/emission from and to surfaces and it will contribute to his perception of temperature and feeling of comfort. It is easy to identify radiation from warm surfaces, but radiation to a cold surfaces is often wrongly identified as air movement (draft). If it is both a warm and a cold surface in the same direction the person will feel the sum of them and they will compensate each other. This is the reason for always place radiators on outside walls and under windows in the rooms. Placing radiators on partition walls and especially opposite outside walls, is a design error. The BREEZE simulations calculate surface temperatures and will therefore be able to calculate the effect on the comfort considering radiators.
- Air movements.
Air movement (wind and draft) can have a major effect on the perceived temperature. One sample is the wind chill effect that now is popular to mention in weather reports. Everybody also knows the effect of ventilators during hot summer days. BREEZE simulations do not consider air movements and therefore this must be considered by construction design. A good construction is little effected by outside winds and does therefore include wind breaking wall construction, doors and windows. Air movements can also be caused by cold surfaces, since the cold air close to the surface will move downwards by thermal forces. This kind of air movements will cause draft and negatively influence the comfort. This is the reason why ideal placement of radiators is under the windows, where it will both compensate for draft and the radiation to a cold surface. By BREEZE giving surface temperatures, warnings are given for situation where a thermal downdraft can occur for a surface.
- Humidity.
The relative humidity is also an important factor for the feeling of comfort. The air can at a certain temperature only contain a certain maximum amount of water, this is described as 100% relative humidity. Warm air can contain more water than cold air and if warm humid air is cooled down it will condense the surplus of water i.e., fog. If surfaces are colder than air temperature it will cool down the air close to the surface and if the air is humid it will result in condensation on the surface i.e. mirrors in bathrooms during hot showers. The following diagram shows the relationships between temperature, relative humidity and amount of water in the air.
People are dependent on evaporating water from the skin (transpire) to keep an ideal body temperature. If the air is very humid, it cannot take up more water, the evaporation cannot take place and people will feel uncomfortable. This can vary with the metabolism for different people i.e., slim people that do not have to watch the weight, have a high burning rate and will be less effected by warm humid conditions, where people with low burning rate will feel very uncomfortable. Normally people will feel comfortable between 30% to 70% relative humidity. BREEZE simulations do not consider the humidity. By BREEZE giving surface temperatures, warnings are given for situation where a humidity condensation can occur for a surface.
- Symmetry.
The BREEZE simulation also calculates a comfort factor, which considers the directions of which the body radiates the heat. If the symmetry is unbalanced the feeling is uncomfortable i.e. an open fire in a cold room which gives a lot of heat to the front, but the back is very cold. The comfort factor (symmetry) is a measurement of the influence of the difference of temperature of the surfaces.
Description of calculated construction objects.
The calculated house with small terrace is c:a 63 sqm construction with measurements around 8.25 x 7.65 m and 55 sqm living area. It is oriented with is main facade at south. It has 8 windows of which the two largest ones and the door are oriented at south.
- Spanish type 1.
The wall construction is 30 cm Brick walls. The roof is two times bricks with air space. Windows are double insulation glass. Floor is the same for all houses.
- Spanish type 2.
The wall construction is 30 cm Brick - 5 cm air - 15 cm Brick wall from the outside to the inside. The roof is two times bricks with air space. Windows are double insulation glass. Floor is the same for all houses.
- EU suggestion.
The wall construction from the outside to the inside is, 2.8 cm ventilated Wood panel - wind breaker - 10 cm mineral wool - humidity barrier - 2 cm Wood Panel wall . The roof from the outside to the inside is, Tiles - 2 cm Wood panel - 20 cm mineral wool - humidity barrier - 2 cm Wood Panel. Windows are double glass. Floor is the same for all houses. This corresponds close to the suggested EU Building Code, modelled from the Danish, and the prior 1978 Swedish Building Code for permanent houses and the current for summer vacation houses.
- Swedish standard.
The wall construction from the outside to the inside is, 2.8 cm ventilated Wood panel - wind breaker - 20 cm mineral wool - humidity barrier - 2 cm Wood Panel wall . The roof from the outside to the inside is, Tiles - 2 cm Wood panel - 40 cm mineral wool - humidity barrier - 2 cm Wood Panel. Windows are double glass. Windows are double insulation glass with third glass on the inside Floor is the same for all houses.
Simulation results.
For the purpose of this article, we have taken the months of January and August and selected the following constructions from the simulations,
Chart 1. The results from Effective Temperature (Perceived Temperature) in January are very interesting. It confirms the personal experiences from a large number of people. The air temperatures in Spanish houses are normally 3º to 5º higher for the Spanish construction, for a similar feeling of comfort as in the Nordic construction. This means that in this cases when the air temperature have been set to 22º, Spanish type 1 need a 1º higher (23º) room temperature, EU suggestion 2º lower (21º) and Swedish standard 3º lower (19º) room temperatures, to equalize the temperature sensation in the buildings. The extra gains in January energy use for the EU and Nordic constructions can be 10% to 25% better than our simulations indicate.
Chart 2. The results from Effective Temperature (Perceived Temperature) with AC in August, all fall within acceptable values and show little difference. Without AC the heavy construction in the Spanish houses have significantly lower peak temperatures during the day time, but night time temperatures are significantly higher.
Chart 3. Comfort values for the different constructions in January. The comfort coefficient in BREEZE is a value that is lower with higher comfort, since it is a value that describes the unbalances in temperature distribution. In the chart we have taken 2.5-coefficient, to make higher value a higher comfort. This is only done for presentation and comparison purpose. As we can see, the January comfort values for the EU and Swedish Building Code are significantly better than the Spanish constructions. The same comfort values for August does not show any significant differences between the construction alternatives and is therefore not included.
Chart 4. Energy and power use for heating in January. This chart is quite self explanatory. Prices for kWh in the calculations, are 1997 prices in Pesetas. Today we use 1 Euro = 166 Ptas and the cost of 16 Ptas/kWh have gone up with around 40% to 50%.
It is very significant differences between the constructions and it give an additional background to the EU suggestion for common minimum Thermal Building Codes.
Chart 5. Energy and power use for cooling in August. This chart is quite self explanatory. Prices for kWh in the calculations, are 1997 prices in Pesetas. Today we use 1 Euro = 166 Ptas and the cost of 16 Ptas/kWh have gone up with around 40% to 50%.
It is very significant differences between the constructions and it give an additional background to the EU suggestion for common minimum Thermal Building Codes.
Conclusions.
Normally when we do a project, it is a specific project and often one that is going to be built. Sometimes it is a project were we are asked if a situation could be changed. In research it can be studies of general situations of interest, but to transform this to implementations can be difficult. The project with Spanish bungalows is interesting, because it is more of a product comparison and it at the same time highlights a general worldwide situation.
The comparisons are simple and the results very definite. This if you accept that the simulation method, which has been well tested by research and thousands of projects, is correct and working.
- Confirmation of possible energy savings.
The simulation comparisons quantifies and confirm the savings that can be done. It is a good correlation with other research and data in the EU suggestions for an European Thermal Building Code. The energy savings are considerable and between 65% to 80%.
- Confirmation of Effective Temperature.
The simulation comparisons confirms the validity of using Effective Temperature as a more correct measure of comfort. The traditional differences of real commonly used room temperatures in Spanish and Swedish accommodations, correlate to the results of the simulations.
- Confirmation of EU suggestion for Building Code.
The method used by EU to find a suitable model for common Building Code, is based more on statistical analyses than on detailed technical analyses. Due to the timing of renewal cycle, the method will give preference to Building Codes that been in place for a long time and are proven. The Danish (prior 1978 Swedish) stands out as superior, because it is basically sound and have been implemented more than 40 years. It also stands out because it was in force during the industrial building boom in Denmark. If the new 1978 Swedish Building Code would have been implemented 20 years earlier, it is likely that it would show major benefits compared even to the Danish.
The simulation comparisons confirms the technical validity of the EU commissions choice of the Danish Building Code and the probable effects of its implementation.
- Confirmation of influence from surface temperatures.
Since the validity of Effective Temperature is confirmed by the correlation between simulations and realities, the influence of the importance of surface temperatures are also confirmed. The acknowledgement of this can result in significant improvements in design practises.
- Illustration of the effects and how the constructions energy storage works.
The simulation comparisons show the needed energy use, explicit both in size and time. Any major or minor failure to supply the energy at any specific moment of time, will result in the energy to be stored in the construction. Lack of or excess of energy at a moment of time, will have to compensated in a later moment of time. The compensation in itself will create an energy waste and/or a loss of comfort.
- Illustration how Peak demands can build up.
Since the simulation comparisons show how the energy storage works, it also explains how a predictable peak demand build up itself. Due to failure to deliver or too high delivery, the storage in the construction will be effected. If the control system and/or control policies (like advices/equipment for turning of or change room temperatures), it will result in a later need of compensation. If the control policies are commonly applied, the compensation will be predictable both in time and size, this will of course result in an excess peak demand. The alternative is to instead use the storage to minimize the peak demand by in an intelligent way place it in periods that otherwise would have a lesser demand.
- Guidance for design of control system.
Since simulation comparisons show the needed energy use, explicit both in size and time, it is possible to design control system and policies that satisfy this. The current traditional control systems and policies, are designed to eliminate the influence of the energy storage in the construction. The result is large energy waste.
The simulation comparisons of bungalows in Spain are very useful as an illustration of the basics of what we want to communicate.
Hakan Falk
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