Savings from High Efficiency Replacement Tank-Type Domestic Hot Water Heaters in Multifamily
Domestic hot water (DHW) heating can account for almost 30% of the total energy use in apartment buildings, not counting the energy used for lighting and electric appliances. Perhaps the best opportunity for efficiency upgrades to DHW heating in multifamily buildings is at the time of equipment replacement. In order to measure savings and assess performance of the "best available technology" for this application, high efficiency condensing tank-type water heaters were installed in parallel with existing conventional tank-type DHW heaters in two apartment buildings. All tests were conducted using an alternating mode design monitored by a computerized data acquisition system.
Savings for the high efficiency replacement DHW heaters were about 28% of annual DHW consumption, corresponding to savings of 24 MBtu per year and 26 MBtu per year for the two cases investigated. Seasonal efficiencies of the condensing DHW heaters were measured at 78% and 81 %. Comparable efficiencies for the standard DHW heaters were 56% and 58%.
Commercially available high efficiency tank-type water heaters are currently too small for larger buildings in which the DHW load (and therefore savings potential) can more readily justify the higher cost of this type of equipment to the owner. Paybacks found in this study were 19 to 20 years even when based on the incremental cost of using a high efficiency DHW heater over a conventional tank-type heater at the time of required heater replacement.
While one heater operated flawlessly throughout the test period, the other had problems with periodic failure of the igniter and tank leaks, indicating that this technology is not yet problem-free. This is a big deterrent for equipment intended for use in multifamily buildings since these owners are very sensitive to tenant complaints and are desirous of maintenance free mechanical equipment. As a result, development of more options for replacement DHW heating equipment for this sector seems warranted.
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Measured Savings from High Efficiency Replacement Tank-Type Domestic Hot Water Heaters in Multifamily Buildings