Advantages of Water-loop
Advantages of Water-Loop Heat Pumps
- They don't require wall openings to reject heat from air-cooled condensers,
- They aren't exposed to the weather and therefore tend to have a longer service life,
- If a unit fails, the entire system doesn't shut down, however, failure of a loop pump, heat rejection device or secondary heater can affect the entire system.
Unitary air and water source heat pumps are available as larger capacity commercial self-contained units which serve large zones using ducts for air distribution. Air-source units must be located along outside walls or on the roof. Note: They tend to have higher operating costs than central plants or water-source heat pumps.
Water-source units can be located anywhere but require ventilation air ducts. They are usually connected to a cooling tower circuit for heat rejection when they are in the cooling mode and to a central hot-water heater or strip heater when heating is required. Advantages include low first cost and the availability of optional accessories (variable air volume control, economizer cycle, night setback, and morning warm-up).
Large system heat pump applications are often applied in buildings using two- or four-pipe water distribution systems or in industrial applications. Many large buildings require cooling the year-round due to large internal loads from lighting, electronic, and other business equipment. Only the perimeter zones of these structures ever need heating. The warm condenser water from the water chillers serving this cooling load can be used as a heat source. The water-to-water heat pump is piped in a cascade system, using this waste heat to preheat domestic hot water, or provide hot water to satisfy building space or reheat loads. Units are available to heat water from 105°F to 120°F, or even higher if needed. The lower the hot water temperature required, the lower the energy consumption.
In some cases, the units are combined into a single heat recovery chiller with a double-bundle condenser. The house water condenser serves the hot water loop for the building. When the waste heat exceeds the heat requirement, the excess heat is rejected in the second tower water condenser. Thermal storage can also be integrated into this system. Other options include integration with closed loop water-to-air heat pumps or secondary heat recovery from water loop heat pump systems.
Air-to-water heat pumps perform in a similar manner but typically use warm exhaust air as the heat source. They are often referred to as heat pump water heaters and are used in hotels, restaurants, laundries, and other applications needing a lot of hot water.
Many industrial processes have low-level waste heat that must be rejected. Factory-packaged, closed-cycle refrigerant-based heat pumps are available to heat water to 120°F or warmer. Using waste heat for this purpose off-loads cooling towers or evaporative condensers while reducing boiler fuel consumption and the corresponding products of combustion.
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