Timo Kalema, Tampere University of Technology Petri Pylsy, Tampere University of Technology
Abstract
In Nordic countries low-energy and passive houses are mostly individuals designed for a certain building site and use. However, in order to increase the amount of low-energy houses it should be possible for builders to buy buildings with certain energy performance and costs. This paper presents results of a project, in which these concepts were developed for the use of building manufactures.
The annual energy use for heating for single-family houses fulfilling the new Finnish building regulations is in the weather conditions of South-Finland approximately 140 kWh/m2/a in which the share of hot water heating is 35 kWh/m2/a. This energy use is obtained with the new reference U-values for the exterior envelope, a 30 % efficiency for heat recovery from exhaust air and using for the tightness of the envelope the value n50 = 4 1/h.
Concepts including the thermal insulation of the building’s envelope as well as the main features of the heating and the ventilating systems for achieving an energy consumption for heating of 100 – 20 kWh/m2/a are
analyzed. The analysis includes calculation of energy consumption for heating and the total costs including the investment and the energy costs. In addition an energy performance grading according to the new Finnish certification system has been calculated.
Without the use of a heat pump the lowest reasonable energy consumption for heating approximately is 60 kWh/m2/a. In this case the U-values of the insulated structures are approximately 0.10 W/Km2 and that of the windows 0.85 W/Km2. The average efficiency of the heat recovery must be high (70 %) and the envelope tight (n50 = 0.6 1/h). Depending on the interest and the repayment time the allowable extra investment cost for this kind of low-energy house is approximately 20 000 €.
With the use of various heat pumps the energy consumption for heating can be reduced up to approximately 30 kWh/m2/a. In this case the allowable extra investment cost is approximately 35 000 €.
Introduction
It has been studied by calculations the following concepts for decreasing the energy consumption for heating of single-family houses:
good thermal insulation and tightness of the envelope efficient heat recovery from exhaust air
various heat pumps as energy saving heating systems
Calculations are made for a 130 m2 single-family house using the weather data of Helsinki. The energy performance grading is calculated using the weather data of Middle-Finland (Jyväskylä), which is the official weather for this purpose. The starting point of calculations is a house fulfilling the present Finnish building regulations. The basic values for energy price are the present ones and a certain increase of energy price is assumed. The basic real interest of calculations is 3 % and the calculation period is 30 years.
Four cases according the thermal insulation level of the envelope have been analysed. The specific transmission heat losses for the four cases are from 104 to 51 W/K. For all levels of thermal insulation four tightness levels of the envelope (n50) varying from 4 to 0.6 1/h have been used. For the annual efficiency of the heat recovery three values varying from 0.30 to 0.70 have been used.
The heat pumps studied are exhaust air, outdoor air and ground heat pumps. The last ones can have either a ground coil or a drilled well as a heat source. Exhaust air and outdoor air heat pumps cover only a part of the heating load. The basic heat source can be either electric heating or district heating.
Finland has taken into use from the beginning of the year 2008 an energy performance grading for buildings.
The grade is calculated from the total use of heating energy as the sum of the energy use for space and hot water heating and for the space cooling (Qsh,, Qkwh,,Qsc), the heat losses of technical systems (heating and hot water devices) Qhl and the electricity consumption of technical equipment Eeq divided by the gross floor area Agf. The heat generation efficiency is not taken into account otherwise, but as heat losses of the heat generation system.
Equation for calculatingthe energy performance grade(ET) or the total use of heating energy/gross floor area is
Energy performance grade A is defined so, that the value of ET is less than 150 kWh/m2/a. Buildings just fulfilling the building regulations usually have an energy performance grade D, in which the total use of heating energy is 190 – 230 kWh/m2/a.
The following quantities for energy (Chapter 6) have been used:
- Energy use for heating is a net energy for space and hot water heating
- Energy consumption for heating is the purchased heating energy (fuel, electricity). It is calculated from the former by using a generation efficiency (coefficient of performance for heat pumps)
- Total use of heating energy is a quantity used in the Finnish energy certification system. It includes the energy quantities of Eq. 1. However, it does not take into account the energy saving due to a heat pump and not the flue gas heat loss of a boiler. Therefore electric heating systems having small heat losses of technical equipment have the best grading.
The results for energy are presented as specific values calculated per floor area. The specific values for the two first energy quantities are calculated for a fixed interior floor area and for the last one according to the Finnish system for a gross floor area, which includes the area taken by the insulation of exterior walls.
Input data of calculations
In the basic case of calculations (Case 1) the U-values of the components of the exterior envelope are according to the present Finnish reference values of building regulations. In addition to this three better thermally insulated envelopes (Cases 2 – 4) have been studied (Table 1).
The interior floor area of the single-family house studied is 130 m2. Figure 1 presents the simple floor plan used in the analysis. The windows’ area/floor area is 12 %. The windows are mainly facing towards south (53 %) and towards north (38 %). Table 2 presents their total solar transmission coefficients. The house is a wood frame house having a massive floor and its thermal capacity/floor area is 70 Wh/(m2K).
When improving the thermal insulation of the envelope the gross floor area calculated according to the outer dimensions increases from Case 1 to Case 4 by approximately 9 % due to thicker thermal insulation layers in exterior walls. This means that the increase of the floor area improves itself the calculated energy performance by 9 %. Naturally the improvement of the thermal insulation improves the energy performance much more.
The hot water consumption is 200 dm3/day and the internal heat gains 7.5 W/m2 on the average. The annual mean exterior temperature is 4.3 oC and the solar radiation on a horizontal surface 936 kWh/m2/a (weather data of Helsinki).
Figure 1. Simple floor plan of the single-family house studied.
Table 3 presents the heating systems studied, their investment costs and their estimated service costs for a 30 years period. Table 3 also includes the energy prices used and their somehow arbitrary estimated rates of increase. It has been estimates that the price of heating oil increases noticeably more rapidly than that of electricity or district heating.
The investment costs include the energy source, a water based floor heating for heat distribution (not in electric heating) and a separate hot water storage (electric heating). Electric heating, district heating, oil heating and heat pump heating using a drilled well as a heat source are basic heating systems, which can alone manage the full heating load. Air-to-air heat pumps and exhaust air heat pumps are additional heat sources for reducing the energy consumption.
For the annual efficiency of the heat recovery from exhaust air to supply air three values (30 %, 55 % and 70
%) are used and for the tightness of the building’s envelope four values (n50 = 4, 2, 1 and 0.6 1/h). The basic value for real interest is 3% and that for the calculation period 30 a.
The energy performance grading for the cases studied is calculated according to the Finnish system. It includes default values (Table 4) for internal heat gains and rather high values for the electricity consumption of
technical equipment and for the heat losses of technical systems.
Table 1. U-values for the exterior envelope for the four cases studied.
* Exterior envelope insulated according the present building regulations Table 2. Properties of the envelope, windows and the gross floor-area.
Unit Case 1 Case 2 Case 3 Case 4
Specific heat loss W/K 103,8 85,8 61.8 50.8
Average U-value W/Km2 0.27 0.22 0.16 0.13
Gross floor area m2 142 145 151 155
Relative gross floor area % 100 102 106 109
Solar transmission of windows 0.567 0.567 0.567 0.45
Table 3. Properties of heating systems, their investment and service costs and energy price for a 30 years period.
System
Water based floor heating 3700 800
Table 4. Default values for electricity consumption of technical equipment, heat losses of technical systems and internal heat gains for a small house. Finnish energy certificate system.
Energy kWh/m2/a
Electricity for technical equipment 50
Heat losses of technical systems 26
Internal heat gains 66
Results
The energy use for heating for the single-family houses studied for the Helsinki weather including the space heating and that of hot water heating is from 140 to 55 kWh/m2/a calculated per interior floor area. The share of hot water heating in these numbers is 35 kWh/m2/a and the share of space heating 105 – 20 kWh/m2/a. With the thermal insulation level of present building regulations (Case 1) the energy use for heating is 140 – 105
kWh/m2/a. With the use of a very tight envelope and a heat recovery system with a high efficiency the energy use for heating can be reduced approximate by 35 kWh/m2/a (30 %). With the best level of thermal insulation
(Case 4) the energy use for heating is 85 – 55 kWh/m2/a. Also in this case the use of the best tightness and the best heat recovery reduce the energy use for heating by 35 kWh/m2/a.
The following effects on the energy use for space heating can be seen from Figure 2:
- The effect of the tightness between the best and the worst envelope is approximately 10 - 15 kWh/m2/a - The effect of the efficiency of the heat recovery system between the best and the worst heat exchanger
is approximately 20 kWh/m2/a
- The effect of the envelope’s thermal insulation is at its maximum 50 kWh/m2/a.
Annual heating demand of the single-family house
0
n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6
30 % 55 % 70 % 30 % 55 % 70 % 30 % 55 % 70 % 30 % 55 % 70 %
Case 1 Case 2 Case 3 Case 4
Thermal insulation, efficiency of heat recovery and tightness of the envelope
Heating demand, [kWh/gross floor area/a]
Space DHW
Figure 2. Energy use for heating/interior floor area of the single-family house depending on the thermal insulation of the envelope, the efficiency of the heat recovery and the tightness of the envelope.
The energy consumption for heating/interior floor area (energy consumed in the building as electricity, district heating or fuel) has a very high spread, 180 – 20 kWh/m2/a (Figure 3). The lowest energy consumption is obtained with heat pumps having a drilled well as a heat source. The boilers have the highest energy consumption due to flue gas heat losses.
The total use of heating energy/gross floor area, the official Finnish energy grading (ET), calculated using the values of building regulations (Table 4) is from 230 to 120 kWh/m2/a (Figure 4). These are high values when compared e.g. with the energy consumption of the passive house definition, which is 15 kWh/m2/a for space heating or when compared with the heating energy consumption of Figure 3.
There are two reasons for the high total use of heating energy. First the energy use for space heating in the Finnish climate is approximately a double compared with that of Central-Europe. Second the values used for the electricity consumption and for the heat losses of technical systems are default values of Finnish building regulations. These values are rather high because they are on the safe side and they are meant for the analysis of conventional buildings. It is clear that when buildings are very well insulated and when their total use of heating energy reduces then also the heat losses of technical systems and their electricity consumption reduce. This effect has been taken roughly into account in our calculations by reducing the electricity consumption and the heat losses of technical systems by 50 % from the values of Table 4 for the Cases 3 and 4 having the best insulated envelopes. This change also decreases internal heat gain by approximately 16 kWh/m2/a in water based heat distribution systems.
The energy performance grading (Table 5) for the buildings studied is from D to A (Figure 4) according to the Finnish system. The grading does not take into account the energy saving due to a heat pump and not the flue gas heat loss of a boiler. Therefore electric heating systems having small heat losses in technical equipment have the best grading.
Annual heating energy consumption for various buildings and heating systems
10
n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6
30 % 55 % 70 % 30 % 55 % 70 % 30 % 55 % 70 % 30 % 55 % 70 %
Case 1 Case 2 Case 3 Case 4
Thermal insulation, efficiency of heat recovery and tightness of the envelope
Heating energy consumption, [kWh/gross floor area/a] Electric/District heating Exhaust air heat pump Air-to-water heat pump Drilled well heat pump Oil
Figure 3. Energy consumption for space and hot water heating for various buildings and heating systems.
Annual energy consumption of variously insulated buildings anf their heating systems
100
n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6
30 % 55 % 70 % 30 % 55 % 70 % 30 % 55 % 70 % 30 % 55 % 70 %
Case 1 Case 2 Case 3 Case 4
Thermal insulation, efficiency of heat recovery and tightness of the envelope
Energy consumption, [kWh/gross floor area /a]
Electric radiators with heat recovery Water based floor heating with heat recovery Water based floor heating with exhaust heat pump AB
C D
Figure 4. Total use of heating energy /gross floor area (ET) and energy performance grading of variously insulated buildings and their heating systems. Jyväskylä weather.
An allowable additional cost due to energy saving measures depends on the annual energy saving obtained. The highest energy savings are obtained in buildings having heat pumps utilizing drilled wells as heat sources. The smallest energy savings are in buildings having as an energy saving measure only the improvement of the heat recovery system or the tightness of the envelope. When the real interest is 3 % and the calculation period 30 years the allowable additional cost can be 0 … 40 000 € for improving the energy performance from the level of building regulations.
Table 5. Finnish energy performance grading for single-family houses.
Energy performance grading
Total use of heating energy* (ET)/
gross floor area kWh/m2/a
A < 150
B 150 …170
C 170…190
D 190…230
E 230…270
F 270…320
G >320
* Energy use includes space and hot water heating and electricity consumption and heat losses of technical equipment.
Allowed additional cost for certain envelopes and heating systems 30 years, interest 3%, escalation 2,5% except oil 7%
0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000
n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6 n50=4 n50=2 n50=1 n50=0.6
30 % 55 % 70 % 30 % 55 % 70 % 30 % 55 % 70 % 30 % 55 % 70 %
Case 1 Case 2 Case 3 Case 4
Thermal insulation, efficiency of heat recovery and tightness of the envelope
Allowed additional cost, [€]
Electric heating District heating Exhaust air heat pump Air-to-water heat pump Drilled well heat pump Oil
Figure 5. Allowed additional costs for certain level of buildings’ thermal insulation and tightness of envelope as well as for certain heating systems.
Conclusions
It can be designed low-energy single family houses for Finnish climate conditions having an energy use for space and hot water heating approximately 50 – 100 kWh/m2/a. A low energy use for heating is obtained with a good thermal insulation, an efficient heat recovery from exhaust air and a good tightness of the envelope. The total use of heating energy including the heat losses and the electricity consumption of technical equipment for these buildings is 120 – 180 kWh/m2/a corresponding to the Finnish energy performance grades A – C. These numbers don’t include the possible energy saving obtained with heat pumps. With the use of ground or drilled well heat pumps the electricity consumption of heat pumps is 30 – 60 kWh/m2/a. Depending on the energy saving obtained compared with buildings constructed according to the present building regulations the additional investment costs of the low-energy houses can be up to 40 000 € higher than those of the buildings just fulfilling the requirements.
References
Pylsy, P., Development of low-energy house concepts for single-family houses. Diploma work. Tampere University of Technology. Tampere 2008 (still under work).
Calculation of buildings’ energy consumption and heating effect. Guidelines 2007. Ministry of Environment.
Helsinki 2007.
Energy performance of buildings. Guidelines and orders 2007. Ministry of Environment. Helsinki 2007.
Thermal insulation of buildings. Orders 2007. Ministry of Environment. Helsinki 2007.
Dof-Energy. www.dof.fi
Promotion of European passive houses. www.europeanpassivehouses.org
ISO/DIS 13790 (2005). Thermal Performance of Buildings – Calculation of Energy Use for Space Heating and Cooling, ISO TC 163/SC 2. International Organization for Standardisation. Geneva.
Definitions
Energy use for heating Net energy for space and hot water heating. The energy use for space heating is calculated by using the principles of ISO FDIS 13790. In this paper this quantity is calculated per interior floor area.
Energy consumption for heating Energy use for heating divided by the efficiency (coefficient of
performance for heat pumps) of the heat generating system. Calculated per interior floor area.
Total use of heating energy Includes the energy use for heating, the heat loss of technical systems and the electricity consumption of technical equipment. Calculated per gross floor area (outside dimensions) according to the official Finnish system.