Heat Pump Water Heaters Selection and Quality Installation Guide SPONSERED BY: Cape Light Compact PREPARED BY: June 7, 201 2 Contents 1 Background ........................................................................................................................................... 1 2 What Are Heat Pump Water Heaters? ................................................................................................ 2 3 HPWH Performance .............................................................................................................................. 3 3.1 Performance Metrics ...........................................................................................................3 3.2 Performance and Potential Savings .....................................................................................3 3.3 What Affects Performance? .................................................................................................5 3.3.1 Hot Water Usage ......................................................................................................5 3.3.2 Ambient Air Temperature ........................................................................................5 3.3.3 Inadequate Space .....................................................................................................6 3.3.4 Tank Set Point Temperature ....................................................................................6 3.4 Dehumidification .................................................................................................................6 3.5 Interaction with Space Conditioning Systems .....................................................................6 3.6 Reliability and Safety ...........................................................................................................7 4 Selecting Locations for HPWHs .......................................................................................................... 7 4.1 Space Requirements .............................................................................................................7 4.2 Heating and Cooling Considerations ...................................................................................8 4.3 Noise…. .............................................................................................................................10 5 Selecting a HPWH Model ................................................................................................................... 10 6 HPWH Installation ............................................................................................................................... 11 6.1 Size, Weight, and Space .....................................................................................................11 6.2 Managing Condensate ........................................................................................................11 6.3 Drain Pans and Blocks .......................................................................................................12 6.4 Heat traps ...........................................................................................................................12 6.5 Tempering Valves and Set Point Temperature ..................................................................13 7 Operation and Maintenance .............................................................................................................. 14 7.1 Filter Maintenance .............................................................................................................14 7.2 Inspect Condensate Drains .................................................................................................15 7.3 Typical Water Heater Maintenance ...................................................................................15 References ................................................................................................................................................. 16 1 Background Heat pump water heaters (HPWHs) promise to significantly reduce energy consumption for domestic hot water (DHW) over standard electric resistance water heaters (ERWHs). Water heater efficiency is usually described by the energy factor (EF). Typical electric resistance water heaters have EFs of 0.9 or above, which means that the heaters are over 90% efficient in converting electricity into thermal energy in the water heater. New HPWHs have EFs of 2.0 to 2.5, meaning that HPWHs can use less than half the energy that a standard electric tank would require. High energy factors in HPWHs are achieved by combining a vapor compression system, which extracts heat from the surrounding air at high efficiencies, with electric resistance element(s), which are able to help meet larger hot water demands. In New England homes, water heating is responsible for 17% of total energy consumption – the largest energy use in homes after space heating. In the Northeast, 1.4 million households (26%) use electricity as their primary water heating fuel1 and consume – on average – over 2,600 kWh each year to heat water.2 In many cases, switching to a HPWH can cut this consumption in half, saving several hundred dollars per year in the “average” home. Although HPWHs cannot be installed in all locations, they do offer significant energy saving potential. Although HPWHs were first commercialized in the 1980s, they were typically add-ons to existing water heaters (i.e. a heat pump would pump water from a tank water heater, heat it outside the tank, and pump it back into the tank). These systems required specialized knowledge for installation and sometimes required both an HVAC contractor and a plumber to install the system. The development of integrated or “drop-in” HPWHs (where the heat pump and tank are integrated within a single appliance) allowed for easy installation by a single trade (Tomlinson 2002). While integrated HPWHs are not entirely new, earlier residential products (available around 2000) achieved minimal market penetration and experienced reliability issues Recently several manufacturers, including General Electric (GE), Rheem, AO Smith, Stiebel Eltron, and Air Generate, have introduced integrated HPWHs (Table 1). Integrated refers to the fact that the units are packaged replacements for conventional ERWH tanks; they include the hot water tank, heat pump, backup resistance heating elements, and all controls. The demand for these integrated HPWHs has been fueled by higher electricity rates and the availability of various incentives (state, federal, local, utility, etc.) that promote the installation of more efficient equipment. Furthermore, the new Federal water heater standard, which takes effect in 2015, mandates EFs around 2.0 for all new electric storage water heaters with capacities greater than 55 gallons (Federal Register 2010). This regulation will effectively mandate the use of HPWHs in applications with large hot water demands and where electricity will be used to heat water. Figure 1. An integrated HPWH installed in a basement. 1 http://38.96.246.204/emeu/recs/recs2005/c&e/waterheating/pdf/tablewh2.pdf 2 http://www.eia.gov/consumption/residential/data/2005/c&e/waterheating/pdf/tablewh6.pdf 1 Table 1. Key Specifications of some integrated HPWHs currently available in the US market. First Hour Capacity Energy Rating Model (gal) Factor (gal) GE GeoSpring™ 50 2.35 63.0 AO Smith Voltex® 60 / 80 2.33 68.0 / 84.0 Stiebel Eltron Accelera®300 80 2.51 78.6 AirGenerate AirTap™ 50 / 66 2.39 / 2.40 60.0 / 75.0 Integrated 2 What Are Heat Pump Water Heaters? A “heat pump” is a device that moves heat from one place to another; it works much like an air conditioner or a refrigerator. While a refrigerator moves heat from inside the fridge into your kitchen, a heat pump water heater (HPWH) moves heat from your basement or mechanical room into the hot water tank. HPWHs are primarily designed as replacements for standard, electric resistance water heater tanks (ERWHs). HPWHs are able to achieve higher efficiencies (and energy factors) through use of the vapor compression heat pump cycle. Auxiliary electric resistance elements are also installed for reliability and quicker hot water recovery. Most heat pumps operate as “hybrid” devices – i.e. they use the heat pump whenever possible, but built-in controls switch to conventional resistance heating when there are large hot water needs. Figure 2. Simple schematic of HPWH operation. 2 The heat pumps in these hybrid water heaters can heat water at high efficiencies, but the heat pumps have heating capacities lower than those of traditional electric resistance elements. Typical 4.5-kW electric resistance elements, for example, can reliably heat over 20 gallons of water per hour. The heat pump has a lower heating rate; GE, for example, publishes a rate of 8 gallons per hour at 68°F air temperature. This gap illustrates the benefit of a “hybrid” configuration – heat pumps are used when possible for highest efficiency, but resistance heat is used when there’s high demand for hot water. Heaters with larger storage tanks generally revert to backup heating less often than lower- volume heaters. Most HPWHs have several operating modes (manually adjustable by the users): • “Hybrid mode” is typically the default; it uses both the electric resistance element(s) and the heat pump to meet demand, but it uses the heat pump whenever possible to maximize efficiency. • “Heat pump mode” uses only the heat pump. This can improve efficiency, but it dramatically reduces