COMPARISON OF BUILDING TECHNOLOGIES FOR NEARLY ZERO ENERGY BUILDINGS

Abstract

Political targets in Europe focus on nearly zero energy buildings (nZEB) to be introduced by 2020. In Switzerland, cantonal energy strategies define a similar target for 2020. While much experience with high performance building envelopes according to MINERGIE-P ® exist, a large variety of concepts and standards for nearly zero energy buildings have been defined, making it difficult to compare realized nZEB. In Switzerland an nZEB definition is given by the MINERGIE-A ® label. Annex 40 in the IEA Heat Pump Programme (HPP) entitled “Heat pump concepts for nearly zero energy buildings” is investigating heat pump system solutions for nZEB. Task 2 is dedicated to simulation work in order to evaluate performance and cost of different system concepts and to improve design, control and system integration. As starting point an analysis of system concepts for different demand structures (single-family house (SFH), multi-family house (MFH) and office buildings) is accomplished. Residential buildings are modified from the reference building used in IEA HPP Annex 38/SHC Task 44, while for the office building typical layouts of a three and five storey building are used. For each reference building, building technology and specific consumption of energy were varied by simulations in the software Polysun ® . The analyzed criteria are annual costs, energy balance and load match. For the evaluation variable insulation standards are used to enquire the limitation of nZEB balance. Different technology options and combinations are used: airto-water (A/W) and ground-source brine-to-water (B/W) heat pumps, district heating, solar thermal collectors, boilers and cogeneration (CHP) with heating oil, biomass, biogas or natural gas. For meeting the nearly zero energy balance, photovoltaic panels are used on the roof and facade area. Simulation results under the chosen boundary conditions confirm that heat pump concepts with photovoltaic panels to balance the energy consumption have the lowest costs to reach a zero energy balance in buildings with moderate energy consumption up to 50 kWh/(m 2 a). In SFH on MINERGIE-P ® level, A/W-heat pumps are more cost-effective as B/W. Solar collectors tend to increase the cost while not necessarily increasing the performance due to competition with the heat pump and PV surface. In MFH heat pumps and district heating as well as biogas CHP can reach an nZEB balance by just using the roof area. However, biogas CHP has higher costs. The other concepts need an extended area by using the facade for PV generation. B/W heat pumps get more cost-effective with increase of specific heat demand. Regarding load match, though, heat pumps increase the deficit of winter electricity. With solar thermal collectors or cogeneration systems, the load match can be improved. For the office buildings possible concepts with the sole use of PV on the roof area are ground-source heat pumps, district heating and cogeneration with biogas. A limit for the nZEB balance is in the range of 4 storeys. For low building energy demands, district heating is most costeffective, while ground-source heat pumps get cheaper with increasing energy demands. CHP, on the other hand, has the best load match characteristic. Currently, higher integrated concepts as well as retrofit considerations are investigated.