Large Heat Pump/Small Storage Tank Small Heat Pump/Large Storage Tank Heat Pump Capacity 310 kBtu/h 90 kBtu/h Storage Tank Capacity 120 gallon 720 gallon Power Input (Varies with GHX Temperature) 36 kW 11 kW Recovery Time 0.30 hours 5.7 hours Table 1: This table summarizes the design of alternative approaches to produce DHW for a typical apartment building using a GCHP system. Table 2A: Monthly peak heating and cooling loads (kBtu) and monthly energy loads (kBtu/h) for a typical apartment building. Table 2B: Monthly peak heating and cooling loads and monthly energy loads with DHW heating loads assuming a 120 gallon (454 L) storage tank is used. Table 2C: Monthly peak heating and cooling loads and monthly energy loads with DHW loads assuming a 720 gallon (2,725 L) storage tank is used. implications on the size of your electricity bill if your home has a smart meter measuring peak electrical demand as well as consumption. TES has implications for your electric utility. The size of generating stations, distribution grid and transformers needed to get energy to your home, and with some utilities even the type of fuel used to generate electricity, are all impacted by your decisions. Domestic Hot Water Storage Tanks in a GCHP Application Many facilities have predictable and intermittent domestic hot water (DHW) requirements. Occupants in apartment buildings tend to use hot water heavily for a few hours in the morning before heading to work and a few hours in the evening preparing and cleaning up after dinner. When designing a DHW system using a gas boiler or gas water heaters, there is little impact on the capital cost on the system. It may cost less to increase the capacity of the boiler and decrease the storage tank size when space in the mechanical room is limited. The following example illustrates the impact of TES on a GCHP system. A typical apartment building was selected to illustrate the impact of DHW production using a large heat pump/ small storage tank compared to a small heat pump/large storage capacity combination. The following assumptions April 2013 were used to calculate heat pump and storage tank capacity (Table 1): • 84 showers over two hours consuming 966 gallons (3657 L) of water between 6 and 8 a.m., plus 483 gallons (1828 L) between 6 and 8 p.m.; • Makeup water temperature: 55°F (12.8°C); and • Water temperature to showers: 110°F (43°C). An energy model was created for the project and DHW loads were added to create three sets of loads: • Building heating and cooling only; • Heating and cooling with 310 kBtu/h (90.0 kW) heat pump /120 gallon (454 L) storage capacity; and • Heating and cooling with 90 kBtu/h (26.4 kW) heat pump/720 gallon (2725 L) storage capacity. Monthly peak heating and cooling loads and monthly energy loads derived from the energy models are shown in Table 2. These were used to calculate size of the GHX for the alternatives using commercially available GHX design software using “g” functions (non-dimensional temperature factors that calculate a borehole field response to heat injection and heat extraction pulses). The length of the boreholes was calculated using the following parameters. Results are summarized in Table 3. • Grid of five boreholes by four boreholes with 20 ft (6.1 m) spacing between boreholes; ASHRAE Journal 15