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Why: Benefits of this Typology This retrofit is particularly useful for buildings where each apartment has an air handler and ducting to each room. Ducted split heat pumps have matured over the past few decades to the point where 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. Each apartment’s heating and cooling system consists of a single outdoor unit and a single indoor unit integrated into the air handler, with refrigerant piping in between. Refrigerant pipe length requirements for these residential scale units is a maximum of around 160 ft, and performance increases with shorter line lengths. Keeping the piping runs as short as possible, the outdoor unit should be placed on the exterior wall of the apartment, on the ground outside, or on the roof, if space is available. The best location may not be where the existing AC condenser unit is. Low-rise buildings typically have adequate ground space, or the exterior walls are accessible enough to realize this optimal placement. The indoor fan coil uses the same power as an existing furnace air handler as the air handler fan moves the air over the coil. The outdoor unit requires 230V service and can either be connected to a common area circuit or tied into 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 the newly transferred cost of heating to the apartments can be viewed as a cost savings for the building owner. In contrast, connecting the outdoor unit to the common area electricity account ensures that residents are not burdened with the cost of heating and cooling. 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.56 Why Not: Plausibility Concerns This retrofit is plausible for buildings that use ducted air handlers for heating and cooling. Adding ductwork can be challenging, though some apartment layouts may allow for a fairly simple and effective short-ducted retrofits. Ductless split systems can have higher-rated heating performance, though installed performance may vary, and ducted systems can have better field performance if properly installed. 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 from $1-3 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 outdoor units 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 units. There are guides to good installation and design practice that need to be followed.57 The ducted split heat pump retrofit makes the most sense in climates that require both heating and cooling, and it is important to size the system based on the larger design load. Available Technology There are several dozen manufacturers of split heat pump systems. An excellent resource for ccASHPs is the product listing maintained by the Northeast Energy Efficiency Partnership (NEEP).58 A single manufacturer provides the outdoor and indoor units, integrated controls, and piping requirements for installation. Steven Winter Associates,Inc. 34PDF Image | HEAT PUMP RETROFIT STRATEGIES FOR MULTIFAMILY BUILDINGS
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