COST MODEL | HEAT PUMP ENERGY SYSTEMS independent heat interface units (HIUs) and/or cooling interface units (CIUs) by providing hot water, space heating and/or comfort cooling within each flat or mixed-use commercial space using radiators, underfloor heating, fan coil units or heat convectors, for example. Hot water is provided by a localised cylinder, which is charged by the heat pump. Savings can be increased with a dual heating and cooling pump energy system, for simultaneous operation. Compared with conventional high-pressure heating systems using HIUs in flats, a heat energy system is more efficient, because lower temperatures reduce the community energy losses from 25-30% to 2-5% and as a result of lower distribution temperatures overheating in risers and corridors is reduced significantly. The units can be supplied in prefabricated, selfcontained modular sections, reducing installation times and onsite labour hours, and offering design coordination and commissioning benefits. Other potential construction costs that can be considered when designing a heat pump energy loop system include reduced sizes of distribution pipework, compared with traditional carbon steel for low-temperature hot water (LTHW) and chilled water (CHW), and a reduction in thermal insulation. The initial costs of installing a heat only pump energy system are more expensive, but savings can be achieved: n Carbon tax payment per flat can be reduced by 40-45% n Plantroom spaces can be decreased in size by 40-50% n Riser spaces increased similarly by 40-50% n Cost per kWh thermal reduced by 25-30% n Tenant running costs reduced by 15-20%. Cost model A traditional heating and cooling design, consisting of a 450kW gas boiler and a 70kWe gas CHP unit linked to HIUs, providing heating and hot water to each flat. Residents are provided with cooling via a 560kW centralised chiller on a dedicated chilled water network linked to CIUs. The heating-only table shows a net increase in development costs of up to 2,415 per flat by adopting a heat pump energy system for a heating-only scheme, compared with one using CHP and a gas boiler. By using heat pump technology as the central plant, and offsetting carbon tax payments, the total net increase in development costs is reduced to 1,645 per apartment. The heating and cooling table shows a net saving in development costs of 150 per flat by adopting a heat pump energy system for a heating and cooling scheme, compared with one using CHP and a gas boiler with chiller. With the addition of using heat pump technology as the central plant, and offsetting carbon tax payments, the total net savings increase to 1,850 per flat. CJ The cost model is purely for M&E installations and takes no account of changes to building elements PAUL BARNARD is an associate and CRAIG THOMAS a project surveyor within the London MEP cost management team at Aecom Heating only Description Cost per apartment Additional plant costs per apartment 4kW heat pump cylinder combination unit in apartment Instantaneous domestic hot water (DHW) and heating production in each apartment Sub-total 3,700 1,000 4,700 Generated savings against traditional systems HIU for each apartment, including installation Meter for HIU Cost to fit and commission meter Boiler size reduction Thinner insulation specification on riser/corridor pipework Savings on valve sizes and spindle lengths (four per apartment) Reduction in pipe size on apartment spur from 28mm to 22mm Change from copper to plastic Removal of modifications to smoke-extract system for corridor purge ventilation (overheating abatement) Sub-total (1,000) (150) (550) (120) (50) (70) (20) (25) (300) (2,285) Net cost/saving per apartment 2,415 Changing central plant to a heat pump, removal of technologies such (300) as PV to achieve carbon compliance (470) Carbon tax saving from changing to a heat pump (770) Sub-total Total net cost/savings cost per apartment (potential) 1,645 Heating and cooling Description Cost per apartment Additional plant costs per apartment 4kW heat pump cylinder combination unit in apartment Additional cost of cooling in heat pump Additional 50l buffer tank or 7m of 100mm pipework for fan coil Upgrade of fan coil to work with heat pump Instantaneous domestic hot water (DHW) and heating production in each apartment Sub-total 3,700 350 300 300 1,000 5,650 Generated savings against traditional systems HIU for each apartment, including installation CIU for apartment, including installation A meter for each of the heating and cooling HIUs Cost to fit and commission heat meters Boiler size reduction Thinner insulation specification on riser/corridor pipework Savings on valve sizes and spindle lengths (four per apartment) Reduction in pipe size on apartment spur from 28mm to 22mm Change from copper to plastic pipework Removal of modifications to smoke-extract system for corridor purge ventilation Removal of chilled water distribution from building risers and corridors (changing from four pipes to two pipes) Removal of cooling pipework in apartment (changing from four pipes to two pipes) Sub-total (1,000) (1,000) (300) (1,100) (120) (50) (140) (40) (50) Net cost/saving per apartment (150) Changing central plant to a heat pump, removal of technologies such as PV to achieve carbon compliance Removal of chiller if adjacent to water source Carbon tax saving from changing to a heat pump Sub-total (300) (1,000) (400) (1,700) Total net cost/savings cost per apartment (potential) (1,850) (300) (1,500) (200) (5,800) Heating only and heating and cooling cost comparison 50 September 2019 www.cibsejournal.com CIBSE Sep19 pp49-50 Cost Model.indd 50 23/08/2019 16:28