Section 3: Heat pumps

  1. Section 3

    Section 3

    3.1 Introduction This section gives guidance on specifying heat pumps to provide space heating and domestic hot water in new and existing buildings to meet relevant energy efficiency requirements in the Building Regulations. The heat pumps covered in this section take heat energy from a low temperature source and upgrade it to a higher temperature at which it can be usefully employed for heating. The guidance covers measures, such as additional controls, that can be used to gain heating efficiency credits to improve the coefficient of performance of heat pumps. For guidance on reverse cycle heat pumps that also provide cooling, see Section 9 of this guide. 3.2 Scope of guidance The guidance in this section applies to the commercial heat pump systems identified in Table 10, which categorises the different types of heat pump according to: • the source of the heat • the medium by which it is delivered, and • the technology. ****Table 10   Heat pump types and associated test  standards**** 3.3 Key terms Coefficient of performance (COP) is a measure of the efficiency of a heat pump at specified source and sink temperatures, but may not accurately represent installed performance: Heating COPheat output / power input                                             Equation 4 % COP (COP100) is the heat generator efficiency. Effective % COP is the % COP with heating efficiency credits. The COP of a heat pump should be determined in accordance with the appropriate test standard identified in Table 10. The input power items to be included in the calculation are defined in the standard. Seasonal coefficient of performance (SCOP) is the overall coefficient of performance of the unit for the designated heating season. It makes general assumptions about the amount of auxiliary heating needed to top up the space and water heating available from the heat pump. SCOP is measured in accordance with the procedures in BS EN 14825:2013 Air conditioners, liquid chilling packages and heat pumps with electrically driven compressors for space heating and cooling. Testing and rating at part load conditions and calculation of seasonal performance. The National Calculation Methodology for calculating carbon dioxide emission rates from buildings uses SCOP. Seasonal performance factor (SPF) is another measure of the operating performance of an electric heat pump over the season. It is the ratio of the heat delivered to the total electrical energy supplied over the season, but there are up to seven different ways to draw the system boundaries. For example, SPFH2 excludes auxiliary resistance heating while SPFH4 includes it – making a large difference. SAP 2012 calculations (for dwellings) use SPF – either measured values for products listed in the Product Characteristics Database, or the default values in Table 4a for products not listed there. The Microgeneration Certification Scheme installation standard, MIS 3005, uses SPF to calculate system performance (although the heat pump product standard, MCS 007, currently specifies a minimum COP). Seasonal primary energy efficiency ratio (SPEER) is an emerging rating figure reflecting the use of primary energy for all types of heat pump, fossil fuel boiler and gas-driven cogeneration technologies, as well as hybrid systems where solar heating or a heat pump is backed up with electric heating or a fossil fuel boiler. Energy labelling with the SPEER will be mandatory from 2015 under the Energy Labelling Directive. Testing and rating will be in accordance with BS EN 14825, as for SCOP. 3.4 Heat pumps in new and existing buildings At the time of preparation of this guide, European Commission Regulation No 206/2012 sets standards only for the SCOP of electrically-driven air-to-air heat pumps with an output  12 kW. There are currently no European test standards for part-load testing of air-to-air heat pumps with an output  12 kW or for other types of heat pump17, and so the performance of these must be specified using COP obtained at the heating system rating conditions. The current recommendations in this guide are that heat pumps in new and existing buildings should: a. if air-to-air with an output  12 kW, have at least a SCOP ‘D’ rating for the median temperature range in BS EN 14825 b. or else have a COP which is not less than the value in Table 11 c. feature as a minimum the controls package in Table 12. ****Table11**** For non-residential buildings, the heat pump system can be sized to meet either the full heating and hot water demand or part of it. Economically viable installations provide at least 50% of the heating and hot water demand for the building. ****Table 12 Recommended minimum controls package for heat pump systems in new and existing buildings**** 3.5 Heating efficiency credits for heat pump systems in existing buildings Heating efficiency credits can be gained for heat pump systems installed in existing buildings by adopting the additional measures in Table 13. These credits are added to the % COP to produce the effective % COP. ****Table 13 Heating efficiency credits for additional measures applicable to heat pump systems in existing buildings**** Example: Using heating efficiency credits to achieve the recommended standard for effective % COP for a heat pump installation A proposed system has an air-to-water, electrically-driven heat pump supplying heat to an underfloor heating system. The COP of the heat pump tested to BS EN 14511 is 2.46, which is below the minimum standard recommended by Table 11 for space heating. The minimum controls package recommended by Table 12 is package E, comprising: a. zone control and time control b. heat pump unit controls for: i. control of outdoor fan operation for cooling tower or dry cooler (energy transfer systems) ii. control of external water pump operation and water temperature for the distribution system c. room thermostat to regulate the space temperature and interlocked with the heat pump unit operation. Table 14 shows the heating efficiency credits that can be gained by adding optimum stop control and full zone control. Effective % COP% COPheating efficiency credits2464250% The effective COP is therefore 2.50, which meets the minimum required by Table 11. ****Table 14 Example to illustrate the allocation of heating efficiency credits to a new heat pump**** 3.6 Supplementary information ****Table****