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Where: Use Today and Retrofit Applications Split heat pumps are nearly the same hardware and layout as ductless split air conditioners seen across the world in hot climates. In the past few years, many manufacturers have developed cold-climate air source heat pumps (ccASHP), which are tuned to provide sufficient heating capacity in colder climates such as the northeast U.S. The same hardware used for residential applications can be used in multifamily applications, though there are few examples of multifamily buildings that have implemented this retrofit strategy. There are a few instances of new construction multifamily that use ccASHP for each apartment and have good results. Why: Benefits of this Typology This retrofit is particularly useful for low-rise buildings that use steam. Low rise buildings that use hot water for space heating may more easily use a central heat pump that reuses the hot water distribution. Mini-split heat pumps have matured over the past few decades to the point that field efficiency is good, there is a high-quality installer base, and hardware costs are low enough that installation cost is not an insurmountable hurdle. Low- rise buildings typically have adequate ground or roof space, or the exterior walls are accessible enough to realize this optimal placement. High-rise buildings will have more difficulty in siting outdoor units. The indoor units use little power for the fan coil and can be hooked up to each apartment’s 120V electrical circuit. Often indoor fan coils are powered through outdoor units with wires that are bundled with refrigerant piping. The outdoor unit requires 230V service and can either be connected to a common area circuit or tied in to the apartment circuit if it has 230V service available. Connecting all heat pump components to the apartment meter makes heating and cooling cost allocation simple and transferring the cost of heating to the apartments can be viewed as a cost savings for the building owner. If direct metering is not desired, connecting the outdoor unit to the common area electricity account ensures that residents are not burdened with the cost of heating and cooling. With thermostat feedback and in-apartment controls, residents can be given adequate feedback to encourage energy conservation, while avoiding regulatory issues with direct metering space heating energy in affordable housing. All equipment can be connected to a central control overlay for monitoring and temperature limiting controls, as well as for errors and maintenance issues. The benefit of split heat pumps over a more central VRF system is that the load for each apartment can be matched with a single outdoor unit. in this sense, each piece of equipment can be optimized for the space being served. Field studies indicate that simpler heat pump setups, where the outdoor units are best matched to the load and are not oversized, have the highest efficiency.53 Why Not: Plausibility Concerns While a retrofit of split heat pumps can be less complex than a VRF retrofit, design and installation quality is just as important, which adds to overall project cost. Current cost estimates for multifamily buildings pursuing split heat pumps are around $10 per square foot for a quality installation. The installation cost is significantly higher than a replacement steam boiler, which ranges between $1-3SF. Per square foot. Major drivers of cost are labor and materials for the modifications to the building during installation, and, to a lesser extent, the equipment itself, which has decreased in cost over the past few years. Design of the system is an additional cost that should be included, as proper sizing and layout of the equipment may not be provided by the installer. There are many issues that can decrease the efficiency of the installed heat pumps, including: excessive line lengths, equipment oversizing, poor pipe insulation, and poor siting of outdoor and/or indoor units. A study by CADMUS54 has some discussion of these issues and how they correlate with heating performance. In general, system designers and installers need to thoroughly understand the manufacturer requirements, site-specific considerations for siting equipment, and estimated post-retrofit heating and cooling loads to ensure an efficient heat pump retrofit. At this point in the stage of the technology, it may be more worthwhile to ensure quality installation than to push for incremental hardware improvements from manufacturers. Heat pump systems that utilize split components connected with refrigerant lines have a shorter expected life span than the steam or hot water units they replace. In addition, heat pump indoor units are typically more Steven Winter Associates,Inc. 31PDF Image | HEAT PUMP RETROFIT STRATEGIES FOR MULTIFAMILY BUILDINGS
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