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unable to efficiently meet the heating loads in colder climates such as Mixed-humid and Cold/Very Cold. As described in the Barriers to Consider section below, there are significant technological shortcomings of the current packaged heat pump offerings for use in cold climates. The limitations of the current technology are driven by a few factors. First, PTHPs are generally seen as the least-cost option for heating and cooling by the building industry, and manufacturers have responded by trying to be the least-cost option among competitors, cutting high quality features and technology to do so.41 Second, the size and packaging of the PTHP makes for challenging design of adequate airflow past coils and condensate/ice melt removal. A cold-climate PTHP offering needs to be developed by manufacturers so that moving from a centralized steam system to a distributed PTHP solution becomes viable. There are several manufacturers of packaged heat pump systems including Amana, General Electric, Frigidaire, and Magic-Pak. Of the available units, some use an inverter-driven compressor which allows for incremental efficiency improvement, but those units are not tuned for cold-weather operation and no current product offering has an effective defrost strategy without serious performance compromises.42 Third party controls can be paired with PTHPs for monitoring and occupancy sensing remote control. However, manufacturers differ on the sophistication of controls for other building system integration purposes. The control system of most packaged heat pumps needs optimization to maximize runtime in heat pump mode instead of reverting to electric resistance backup. Many packaged heat pump solutions now have the capability to integrate remote thermostats and controls that can help optimize performance, but the on-board controls typically result in poor efficiency. With project-specific engineering to optimize the control scheme, current PTHPs can likely improve performance reaching nearly the claimed ratings, but it is currently somewhat engineering-intensive to do so. The added controls and installation engineering cost somewhat offsets the low hardware cost of PTHPs. The combination of optimized controls, basic defrost functionality, and cold-weather capacity improvements through hardware component upgrades can make PTHPs a viable technology for the Mixed-humid climate zone and warmer. When: Opportunities for Phased Retrofit While PTACs are easier to replace than radiators, either can be replaced with the packaged heat pump solution when necessary, so this retrofit can be phased to coincide with normal equipment replacement cycles. This is especially true for buildings where no additional masonry or wall opening modifications are necessary (i.e., with existing PTACs). If the packaged heat pumps can be directly installed with no other modifications, then the building can simply start ordering the new part number as they would the old part number and replace worn out units normally. Existing packaged room heaters are typically replaced at a rate of 5-10% per year, so following a normal replacement schedule would have nearly all units replaced after 10 years. Barriers to Consider As described in the Available Technology section, the biggest barrier to the widespread use of packaged heat pumps is that there isn’t a product on the market that can operate in heat pump mode in cold climates where the most heating energy is needed. Current products will work in mild climates, but once temperatures get close to freezing and lower, packaged heat pumps mostly revert to electric resistance heating, destroying the efficiency and economics argument for this retrofit. With all heat pumps, the cost of electricity relative to fuel should be fully analyzed. Large multifamily buildings with steam heating systems tend to have inherent inefficiencies due to steam balancing and overheating, so there is a better chance to overcome the higher cost of electricity. If the performance of PTHPs can be improved through hardware and controls upgrades, then the packaged solution with no distribution losses and good efficiency in cold weather can likely overcome the baseline cost of steam and hot water buildings, but it is still unlikely to have an attractive financial payback. Steven Winter Associates,Inc. 26PDF Image | HEAT PUMP RETROFIT STRATEGIES FOR MULTIFAMILY BUILDINGS
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