Heat pumps in residential and commercial buildings
Air leakage, or infiltration, occurs when outside air enters a house uncontrollably through cracks and openings. Properly air sealing such cracks and openings in your home can significantly reduce heating and cooling costs, improve building durability, and create a healthier indoor environment. It is unwise to rely on air leakage for ventilation because it can't be controlled. During cold or windy weather, too much air may enter the house. When it's warmer and less windy, not enough air may enter. Air infiltration also can contribute to problems with moisture control. Moldy and dusty air can enter a leaky house through such areas as attics or foundations. This air in the house could cause health problems. The recommended strategy in both new and old homes is to reduce air leakage as much as possible and to provide controlled ventilation as needed.
The purpose of the project was to build a low energy and low cost prefabricated house without compromising the comfort. Due to the overall reduced energy consumption in low energy houses the proportion of the heat required for DHW increases from 30% to 40%. This sets new requirements for a heating system. In this residence there are two air to water heat pumps : one for heating (from October to April) and the other for DHW (DHW; all year round).
The former uses outdoor air and the latter indoor exhaust air as its heat source. The SPF of the 4.6 kW heat pump for space heating is 3.0. If auxiliaries such as fans for heat recovery and standby losses of the water heater are considered as well the SPF drops to 2.0.
Heat pumps in residential and commercial buildings
Heat pumps for heating and cooling buildings can be divided into four main categories depending on their operational function:
· Heating-only heat pumps, providing space heating and/or water heating.
· Heating and cooling heat pumps, providing both space heating and cooling.
The most common type is the reversible air-to-water heat pump, which either operates in heating or cooling mode. Large heat pumps in commercial/institutional buildings use water loops (hydronic) for heat and cold distribution, so they can provide heating and cooling simultaneously.
· Integrated heat pump systems, providing space heating, cooling, water heating and sometimes exhaust air heat recovery.
Water heating can be by desuperheating only, or by desuperheating and condenser heating. The latter permits water heating when no space heating or cooling is required.
· Heat pump water heaters, fully dedicated to water heating.
They often use air from the immediate surroundings as heat source, but can also be exhaust-air heat pumps, or desuperheaters on air-to-water and water-to-air heat pumps . Heat pumps can be both monovalent and bivalent, where monovalent heat pumps meet the annual heating and cooling demand alone, while bivalent heat pumps are sized for 20-60% of the maximum heat load and meet around 50-95% of the annual heating demand (in a European residence). The peak load is met by an auxiliary heating system, often a gas or oil boiler. In larger buildings the heat pump may be used in tandem with a cogeneration system (CHP).
In residential applications room heat pumps can be reversible air-to-air heat pumps (ductless packaged or split type units). The heat pump can also be integrated in a forced-air duct system or a hydronic heat distribution system with floor heating or radiators (central system).
In commercial/institutional buildings the heat pump system can be a central installation connected to an air duct or hydronic system, or a multi-zone system where multiple heat pump units are placed in different zones of the building to provide individual space conditioning. Efficient in large buildings is the water-loop heat pump system, which involves a closed water loop with multiple heat pumps linked to the loop to provide heating and cooling, with a cooling tower and auxiliary heat source as backup.
