Ireland's only dedicated building services engineering journal
Ireland's only dedicated building services engineering journal

Fundamentals of Heat Pump Technology

The ground acts as a huge solar collector and thermal store. The surface is warmed by the sun and the adjacent air during daytime and in the summer. Similarly, it is cooled during night-time and in the winter. Fluctuations of ground temperature reduce with depth and stabilise at the annual mean for the location by about 12m below the surface. Typically in Ireland this temperature lies between 9C and 12C, which is suitable for directly cooling many types of building as it is well below summertime comfort temperatures.

Ground Source Systems – Water:

There are two common ways of accessing this stored “coolth” and a number of others for altering its temperature. To access the “coolth” a circuit can be established which is either open loop or closed loop.

Open loop systems: water is abstracted from the ground (typically an aquifer or, if available, a ground or surface water source such as a lake or river), then passed through a heat exchanger to transfer heat to the building systems. Finally the water is either returned to the ground or discharged to a river (or sewer if the local water company can accommodate the additional capacity) however, in this case we would suggest getting help from a sewer pump repair in norfolk va company.

Closed loop systems: according to a patio builder in sydney this comprises a continuous loop of pipework which is buried in the ground. The water that is circulated through the ground loop can also be used by the cooling distribution system within the building. The ground loops can be vertical (up to depths of 100m) or horizontal (typically 2m deep).

Compared with conventional chillers, the energy savings associated with the use of ground water cooling are significant. The only energy requirement is for circulating water, whereas the bulk of energy associated with conventional cooling is for compressors within the chiller plant. A 90% saving in cooling electricity demand is feasible for ground water cooling systems. (The proportion of total energy demand which cooling represents depends on building use and age. Modern well-insulated buildings may have a greater need for cooling in summer).

The technology is commercially viable in many areas when applied to certain building types. The installation costs depend on local ground conditions (solid rock will be more expensive to drill through), or the availability of suitable available surface water. Ground water cooling is best suited to buildings with modest cooling demands (eg, offices, shops and hotels).

Ground Source Systems – Air

Heat pumps use refrigerant gases and an electrical compressor to take heat from a source and deliver it to an output. Chillers and refrigerators are examples of systems that remove heat, but other types of system use the heat removed from a source to heat a building. Traditional heat pumps use air as the source of heat. However, the ideal source for maximum efficiency would be one having a stable temperature, and the ground provides such a source.

Ground-source heat pumps (GSHPs) make use of the heat stored in the ground at this relatively stable temperature of around 9C and 12C and raise it to a more useful output temperature of around 40/50C for in heating buildings. These output temperatures are ideal for low temperature systems, eg, underfloor heating coils and radiant panels in most types of building.

Heat can be extracted from the ground either by a buried loop of pipework through which a refrigerant fluid (or water) is circulated, or directly by abstraction of ground water.

Heat can be extracted from the ground either by a buried loop of pipework through which a refrigerant fluid (or water) is circulated, or directly by abstraction of ground water. With correct design, the depletion of the heat source is matched by the rate of heat flow back from the surrounding earth and, under these circumstances, the technology is a renewable source of energy.

Where GSHPs are installed as an alternative to conventional (resistive) electric heating, carbon savings of 50/70% are achievable. In some circumstances, well-designed GSHPs can result in reduced CO2 emissions when compared with gas and oil fired boilers. The capital costs associated with GSHPs are highly-dependent on local conditions. Capital costs are usually competitive where there are limited gas or oil supplies, and running costs are much more cost-effective than alternative forms of electric heating (which is a particularly poor source of energy for heating in terms of its carbon emissions).

The reliability of heat pump components is good, with expected lifetimes of 20 to 25 years. The expected lifetime for their ground coils is much longer, with warranties being offered for up to 50 years. Capital costs are higher than for alternative systems, mainly because of the civil engineering costs associated with the ground coil. On a life-cycle cost basis, these systems offer a viable option in the context of Ireland’s obligations to reduce both our energy consumption, and CO2 emissions, by the 2020 deadline.

Air source heat pumps

Electric air-source heat pumps use the difference between outdoor air temperatures and indoor air temperatures to cool and heat air within the building. They are primarily used in domestic applications. The most common type of heat pumps is the air-source heat pump, which transfers heat between inside and the outside air.

High-efficiency heat pumps also dehumidify better than standard central air conditioners, resulting in less energy usage and more cooling comfort in summer months A heat pump is typically rated to provide approximately 80% of the peak load of the residence on the coldest day. Since the number of days that we have these extremely low temperatures is relatively low, taken as a percentage of the total year, the heat pump is typically rated to provide 90/95% of the total heating needs for a property over the entire year. The remaining energy is usually provided by another heat source (oil/ gas boiler) or an electrically-heated source.

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