A one-year field study was conducted on five multi-residential buildings to assess the thermal performance and delivery capability of central domestic hot water systems. The buildings were monitored for hot water consumption, natural gas consumption, and hot water load, using digital demand recorders. Consumption profiles were developed with hourly, daily, and monthly breakdowns for three building categories: senior citizen, condominium, and rental. The profiIes showed that hot water consumption is a function of time of day, seasonal factors, building type, and demographics. The overall average hot water use per suite of 64 gallons (242 litres) was found to be very close to the 63 gallons (239 litres) per household reported in a previous ASHRAE Study. Average daily consumption per person was 21 gallons (79 litres), higher than for single dwellings but consistent for multi-residential units. A detailed energy flow analysis was used to calculate the overall system efficiency, which ranged from 52% to 65%, as well as loop, standby, and stack losses. Analysis of the experimental data indicated that significant energy savings can be obtained by reducing loop losses and improving combustion efficiency. Results of this study should be of value in deveIoping design criteria for the sizing of storage and recovery capacities of domestic hot water systems in apartment buildings.

Units: Dual