European Home Energy
Denmark is taking steps to meet, and then exceed, the European Union's Energy Performance of Buildings Directive for single-family homes.
An important aim of the directive is to improve the overall energy efficiency of new buildings. The directive requires a methodology for calculating the integrated energy performance of buildings, standards for the energy performance of buildings, and a labeling scheme for buildings. The new energy performance standards were introduced in Denmark in 2006. The requirements could reduce energy consumption in new buildings by 25%–30% compared to current consumption. According to the new requirements, new houses should meet an energy frame—that is, maximum total energy consumption, including energy for heating, ventilation, cooling, and hot water, but not electricity consumption for household appliances, lights, and electronic devices.
Buildings are classified as ‘‘low-energy building class 1’’ or ‘‘low-energy building class 2.’’ The new classification system will make it easier for building contractors to promote low-energy houses to consumers, and the public will be able to demand that their new houses perform better than the requirements specified in existing building regulations.
The energy frame is calculated as 70 + 2,200/(gross area)(kWh/m2 annual). The Danish Energy Agency specifies that electricity consumption be transformed into primary energy using a factor of 2.5. The measured energy consumptions are corrected for outdoor and indoor climate corresponding to typical assumptions—that is, an indoor setpoint temperature of 68°F (20°C) and an outdoor climate using the Danish Reference Year (DRY).
New buildings with an energy consumption of less than 50% of the energy frame will be classified as ‘‘low-energy building class 1.’’ New buildings with an energy consumption of less than 72% of the energy frame will be classified as ‘‘low-energy building class 2.’’ Buildings that only just meet the requirements are not classified in any specific category.
Demonstrating the Savings
In order to meet these new energy requirements and prepare the way for future buildings with even lower energy consumption, the Associated Danish Distributors of Electricity (ELFOR) and the Danish Energy Authority (ENS) had a number of detached single-family houses built. The houses were built with new types of building envelopes, ventilation with heat recovery, and so on, to demonstrate that it is possible to build typical single-family houses with an energy consumption that meets the demands of the EPBD without serious technological or economic challenges. (See photos throughout for house descriptions.)
In order to see how these occupied homes measured up to the new standards, during the heating season of 2003–4, my colleagues and I at the Technical University of Denmark measured the overall energy use of three of the single-family experimental houses, Houses A, B, and E—the ones that were occupied at the time. We measured electrical consumption for heating and ventilation (pumps and fans) and household appliances. Also, since better-than-the-norm insulation and ventilation with heat recovery reduces heat loss in the homes, we wanted to investigate the influence of ‘‘free’’ heat given off from electric appliances, lights, and electronic devices. In highly insulated homes, the free heat can be significant.
The Experimental Houses
In Denmark today, district heating accounts for 46% of the total net heating demand. The remaining 54% of heating demand is met primarily through individual gas- or oil-fired boilers. Thirty-two percent of single-family houses are heated with district heating systems. The percentage is probably higher in new homes in urban areas. All the occupied houses have in-floor heating systems, are supplied with district heating, and have mechanical ventilation with heat recovery.
The energy-saving measures used in the experimental houses were, in general, as follows: more insulation, better thermal bridge insulation, low-e glazing, insulated window spacers, increased airtightness, and ventilation with heat recovery. The construction expenses for these energy-saving measures were only about 5% of total construction costs.
Homeowners benefit financially from highly insulated houses that use less energy, because their heating and cooling bills are lower, and because highly efficient houses require smaller, less-expensive heating systems. In the case of the test homes, which are heated through district systems, the initial benefit of less-expensive HVAC equipment is lost.
Making the Building Envelope Airtight
An airtight building envelope is required for efficient heat recovery in balanced ventilation systems. The guide on energy-efficient ventilation published by the International Energy Agency’s Air Infiltration and Ventilation Centre (AIVC) recommends an air change rate below 3 ACH at a pressurization or depressurization of 50 Pa. In some countries—for example, Switzerland and Sweden—an air change rate below 1 ACH is recommended or required.
The European Union-funded demonstration project Cost-Efficient Passive Houses as European Standards (CEPHEUS) has proven in practice that high levels of airtightness (between 0.3 and 0.6 ACH) can be achieved in all types of construction in a reproducible manner, and that rigorous planning of airtightness details is the key to success. The project recommendations provide an excellent basis for airtightness. The measured airtightness of the Danish experimental single-family houses was approximately 1.5 ACH.
Following are some of the air sealing measures that were used in the Danish houses:
- A double layer of lath was used in the ceiling construction, making room for electrical installations without disturbing the thermal envelope. (The same principle could be used in constructing lightweight exterior walls.)
- Duct collar (self-adhesive EPDM rubber) was applied to air seal the joint where the ventilation ducts penetrate the plastic foil of the ceiling construction.
- Plastic foil was laid out in such a way that the joints could be sealed with construction-grade adhesive tape.
- The joint between the plastic foil in the ceiling and the inner wall of the exterior wall was sealed.
- The inner surface of heavy exterior walls was carefully filled and painted.
We measured consumption for space heating, domestic hot water (DHW), and electricity in the three occupied houses. In addition, we measured solar radiation, outdoor and indoor temperatures, and temperatures in the heating and ventilation systems. Houses A and B were occupied by families with small children; House E was occupied by two adults.
Consumption of Energy for Heating
Table 1 shows the measured energy consumption for space heating and water heating, including electricity for pumps and fans. The internal heat gains are based on detailed electrical measurements and estimates of how much of the electricity consumed by an apparatus with heat loss (washing machine, dishwasher, and so on) can potentially be utilized for space heating. The contribution of heat from people is based on information from the residents about their use of the house.
The measured space-heating consumption for House A and House B took place over almost the whole of the heating season, which is typically defined as the months of September to May, inclusive. The monitored period for House E is shorter. During the monitored periods, the average indoor temperatures were relatively high, 72°F–73°F (22°C–23°C), compared with a typical design temperature of 68°F (20°C). The same significant deviation between the design temperature and the realized temperature determined by the occupants has been experienced in other demonstration projects. The internal gains are about 4 watts per square meter (W/m2) or 20% less than the 5 W/m2 normally used in calculations.
Consumption of Electricity
Table 2 shows measurements of the total electricity consumption for ventilation; heating; white goods (washing machines and dryers, dishwashers, and other large appliances); and other electric devices. The extent of the electricity-related heat gains that can potentially be utilized for space heating is also shown in Table 2.
The loss of heat from electricity to the outside occurs entirely or in part when an electric cooker, dishwasher, washing machine, tumble dryer, or outdoor lighting is used. We estimated these losses by detailed analyses of the specific losses for the relevant appliances.
We calculated the recoverable heat gains based on the gain-consumption ratio. We assumed that the measuring periods represent overall electricity consumption; therefore the whole-year consumptions are based on linear extrapolation of the consumptions during the measuring periods.
The total measured electricity consumption is normal for typical single-family houses in Denmark; average consumption is approximately 4,000 kWh per year. The electricity consumption for white goods is significant (at 25%–30% of total consumption). There is good coherence between expected energy performance and measured consumption. The highest consumption was measured in House B, which has the least energy-efficient appliances (in the European Union there are energy-labeling requirements for many household appliances—see “Europe’s Energy Labels”). The lowest consumption was measured in House A, which has the most efficient appliances.
Electricity consumption for the heating and ventilation systems is 20%–30% of total consumption. The considerable share of electricity consumption for ventilation in House B is due to the use of typical low-efficiency A/C fans, with consumption of approximately 100 watts. The consumption in Houses A and C is only about 25 to 40 watts with comparable air flow, due to the use of high-performance DC fans. The very low share in House E is partly due to a low air flow rate at the beginning of the period.
The measurements show that about 75% of the heat generated by the electricity consumption can potentially be used for space heating. The remaining 25% is lost outside the building envelope or comes from heated water in dishwashers and washing machines that is not recovered.
We investigated the concrete significance of reduced electricity consumption. Calculation models of the houses were taken as a starting point, based on the measurements made in this study. We compared these calculation models with electricity-saving models—that is, models in which the most energy-efficient appliances on the market replaced the least energy-efficient appliances.
The electricity consumptions and related heat gains that can be used to reduce space-heating consumption are reduced by about 40% in the test houses. However, the effect on the consumption of energy for space heating depends on a number of parameters that are not constant, such as indoor temperature and house orientation. Therefore, parameter variations were made. The indoor temperature is referenced as 68°F (20°C). Higher temperatures are quite typical in the occupied test houses, as the measurements show. Therefore we considered the indoor temperature to be 72°F–73°F (22°C–23°C) in our analyses. Climate data were referenced as DRY, based on 15 years of weather data (1975–1989). However, it would also be relevant to look at the effect of a cold spring or autumn, which could result in a much better utilization of heat gains.
We assumed ventilation with heat recovery. The orientation of the single-family houses is typical of Danish homes and was assumed to be east-west. A north-south orientation would decrease solar gain and thereby the utilization of internal heat gains. The best-case scenario is one with a temperature of 73°F (23°C), a cold spring and autumn, natural ventilation, and a north-south orientation.
Based on calculations of the energy consumption for space heating with and without the electricity savings outlined above, and with the above-mentioned parameter variations, utilization factors and remaining electricity savings can be calculated. The calculations show that the whole-year utilization of electricity-related heat gains does not vary significantly. The typical utilization factor is approximately 0.55—that is, about 55% of the electricity-related contribution of heat can be utilized for space heating. This means that electricity savings of 100 kWh will result in an increase in space-heating consumption of approximately 40 kWh. Because of the relatively high cost of electricity compared to the cost of heating, the savings are only modestly reduced by increased heat consumption. (A savings of $100 would be reduced to about $85, for example.)
Airtightness of Building Envelope
Based on blower door measurements, we calculated the yearly average infiltration rate for the experimental houses. The average airtightness level in Houses A, B, and E at 50 Pa, expressed as average ACH, was 1.5 ACH. This is close to half of the maximum required by the new Danish Energy Regulations of 2006, which is approximately 2.8 ACH. The yearly average uncontrollable infiltration rate was calculated at 0.1 ACH. This is an acceptable level compared to a total required ventilation rate of 0.5 ACH. The measured level of airtightness was achieved through careful planning and careful workmanship, and repair of the inevitable holes that occur during the building process. Therefore, it should not be necessary to apply expensive and complicated technology to achieve a satisfactory level of airtightness.
Overall Energy Use
As mentioned above, the average indoor temperature in the houses during the measuring period was relatively high. This greatly influenced energy consumption. According to the calculations, space-heating consumption can be reduced by 12% in House B and 8% in Houses A and E, respectively, per degree Celsius (equivalent to 1.8°F) of reduced indoor temperature.
We compared the measured energy consumption of the test houses with the performance requirements of the new standards. According to the new requirements, as I explained above, new houses must meet an energy frame; this energy frame is the maximum allowed delivered energy, excluding electricity for household appliances. Corrections were made for House B due to a very large consumption of hot water and electricity for ventilation, and heat loss from heating services.
Based on our measurements, the actual energy consumptions for Houses A and E easily meet the new performance requirements (see Figure 1). Consumption for House B does not meet the requirements. This is primarily due to the very large electricity consumption for ventilation. If adjustments are made with regard to ventilation in House B, the energy consumption for House B will easily meet the requirements. In light of this, House B can be classified as “low-energy building class 2,” and House A and House E come close to achieving that classification.
Henrik Tommerup is a research assistant at the Technical University of Denmark, Department of Civil Engineering, in Lyngby, Denmark.
The work on which this article is based was funded by the Associated Danish Distributors of Electricity (ELFOR) and the Danish Energy Authority (ENS).
For more information:
Contact the author by e-mail at firstname.lastname@example.org.
The status of the EPBD implementation can be followed on the Web at www.epbd-ca.org or www.buildingplatform.org.
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