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an opening in the wall already exists and maintenance requirements for PTHPs are similar to PTACs, making the operations transition relatively simple. Why: Benefits of this Typology Each heater maintains complete independence from other room heaters and the PTHP can be connected to the apartment’s electricity panel. Tenants are thus in control of their own heating and cooling and are incentivized to save energy and money. PTHPs are a relatively simple pieces of equipment and can be maintained by building staff. Compared to a radiator or convector, PTHPs require the additional maintenance of periodic filter cleaning, but compared to a steam or hot water PTAC or a hydronic fan coil unit, the maintenance remains the same. While PTHPs use the same fluorinated gas refrigerants as VRFs and split systems, packaged heat pumps are factory assembled and leak-tested, so there are fewer opportunities for refrigerant leakage from installation. Installation is also simplified since there is no requirement for field leak testing, which requires a return visit by the installer. Centralized fuel-based heating systems make up a large proportion of the overall multifamily fossil-fuel use as shown in Figure 3, across all vintages and styles of building. However, the complexity of centralized heating systems in the existing building stock results in energy waste and challenges in operations and maintenance. Converting to a heat pump system is an opportunity for departure from the centralized heating plant and movement towards a more distributed mechanical setup. Centralized systems burden the building owner and staff with the responsibility of operating the system to meet the needs of the tenants and they make it more challenging to meter usage by each tenant. Centralized systems may be able to tie into district heating infrastructure, which have been shown to have upfront energy benefits38 but can also carry a risk of underground leaks,39 which are difficult to locate and repair in dense urban environments where many multifamily buildings are found. Compared to steam or hot water PTACs, a packaged heat pump replacement may be equivalent in equipment cost. Why Not: Plausibility Concerns There are many different sizes of wall openings for existing steam or hot water PTACs. High-performance PTHPs may not be offered in all sizes, so wall opening modifications could be required to fit new equipment. The envelope work can be coordinated with other required façade work, but wall modifications may add $0.5- $1/SF to a PTHP retrofit. While product design and installation can reduce thermal bridging and air leakage, a PTHP requires a wall penetration that has neither the insulation, thermal mass, nor the air tightness of a solid wall.40 Insulation and air sealing may be sidelined as cost-cutting measures in the design and installation of PTHPs, so care in the technology development and selection, as well as in the skill of the installers, is very important to realizing energy efficiency gains without introducing new energy penalties. The equipment requires an electrical outlet rated for 230V. Any currently available PTHPs that operate using a lower voltage do not have the capacity to meet a typical apartment heating load when outdoor temperatures are below 40°F. With drastic heating load reductions through a heat-load-reducing retrofit, a single room in an apartment in a Mixed-humid or warmer climate may be able to be served by a 120V, 6,000 BTUh or less PTHP or through-wall air conditioner with heat pump heating, but this would require significant envelope and mechanical work beyond the heating system conversion. Available Technology In mild climates, where below-freezing temperatures are infrequent, most PTHPs will work reasonably well because they can maintain operation in heat pump mode. However, most PTHPs currently on the market are Steven Winter Associates,Inc. 25PDF Image | HEAT PUMP RETROFIT STRATEGIES FOR MULTIFAMILY BUILDINGS
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