Heat pump, climate characteristics, conditions of usage, how to install

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8) Choosing a heat pump
When choosing a heat pump it is necessary to bear in mind the following points:
- The climate characteristics of the place where it will be installed.
- The type of building.
- Conditions of usage.

CLIMATE CHARACTERISTICS
Climate characteristics are important above all if the cold source is the external air.

Electric Heat Pump Gas Absorption Heat Pump
During the winter period, frost may form on the evaporator, leading to poor heat exchange. To remedy this inconvenience the heat pump is equipped with a defrosting system (e.g. an electrical resistance or cycle inversion, i.e. temporary operation as air conditioner). During the winter period, frost may form on the evaporator for short periods, with a reduction in heat exchange. To remedy this inconvenience the heat pump is equipped with an automatic defrosting system that ensures the continuous supply of heat to the internal environment in any case (albeit reduced) without the use of other energy or systems (electrical resistances etc).








TYPE OF BUILDING The type of building likewise influences the choice of the type of heat pump. For example:

Electric Heat Pump Gas Absorption Heat Pump
- In residential buildings the heat pump may be installed in the basement or in the boiler room. In this case, noise and condensation do not cause problems and the vicinity of a traditional boiler can make bivalent use of the heat pump possible.
- In tertiary and industrial buildings the outputs required usually make it necessary to install heat pumps on the outside of the building, usually with air as a cold source and a supplementary boiler.
- In residential buildings the heat pump may be installed in the open, without any additional protection. External installation avoids the use of internal space and the risk of transmitting noise to rooms.
- In tertiary and industrial buildings the outputs required usually make it necessary to install heat pumps on the outside of the building, usually with air as a cold source. Usually boilers or other supplementary heating systems are not required.









- In commercial environments such as hairdressing studios, restaurant kitchens, etc, the installation of a heat pump can be a very convenient choice, as the processes of cooling and de-humidification make the working environment more comfortable.

CONDITIONS OF USAGE
Usage conditions, too, influence the choice of heat pump. As has already been mentioned, the heating power of heat pumps varies with changes in the temperature of the cold source and of the hot source. The greater the difference between these two values, the greater is the reduction in heating output, and vice versa. The choice of a suitable heat pump therefore depends also on the usage of both the cold source (i.e. air or water and its temperature) and the hot source (water for heating at a low or medium temperature).

9) Sizing
Decisions regarding the sizing of a heat-pump-based system require an accurate evaluation of heating requirements: overestimation, with an oversized heat pump, entails an increase in system costs and consequently a reduction in the economic benefits which derive from its use. It is wise, therefore, to have a qualified technician evaluate the appropriate dimensions.

AIR CONDITIONING
Electric Heat Pump Gas Absorption Heat Pump
A reversible-cycle heat pump has a cooling capacity which is slightly lower than its heating capacity, supplying, in the case of an air/water heat pump, water at a temperature of up to 7ºC. A reversible-cycle heat pump has a cooling capacity of approximately half its heating capacity, supplying, in the case of an air/water heat pump, water at a temperature of up to 3ºC.





HEATING OF INTERNAL ENVIRONMENTS
Heating requirements depend on geographical location: particular attention should be given in the case of heat pumps that use air as an external source, since the amount of heat supplied falls when air temperature falls.

Electric Heat Pump Gas Absorption Heat Pump
Heat supplied to the hot source, in the form of hot water usually between 35° and 50°C (except during the defrosting phase). Heat supplied to the hot source, in the form of hot water, may reach 60°C (without being significantly affected by the defrosting phase).





10) Installation of Heat Pumps
Heat pumps have attained high levels of reliability, but require correct installation and a minimum of maintenance in order to maintain good performance over time. As with decisions regarding sizing, it is advisable to consult specialised installation experts.
The following practical advice is may be useful to the user in order to focus upon the problems connected with the installation of the equipment:
- It is essential to prevent the formation of condensation by using adequate insulation in pipes that carry cold liquids.
- The operation of the heat pump is regulated by a thermostat, either directly or indirectly, which is sensitive to room temperature, with on/off cycles. To reduce the number of operation cycles and extend the useful life of the heat pump, it is sometimes advisable to install an inertial tank in the system.

Electric Heat Pump Gas Absorption Heat Pump
It is advisable to check that the minimum operating temperature of the heat pump in the location in which it is installed is not lower than the minimum temperature of the outside air. Otherwise it will be necessary to install a supplementary boiler. The minimum outside operating temperature is -20ºC (20º degrees below zero).




- It is advisable to provide adequate drainage for the condensation that forms upon the evaporator, for example by means of a suitable basin or a drainage pipe.

Electric Heat Pump Gas Absorption Heat Pump
Finally, it is necessary to stipulate an electricity contract which guarantees adequate electrical power to ensure the operation of the heat pump which has been chosen (higher than the 3 kW generally provided for domestic usage) and to have qualified installation technicians carry out the initial start-up of the system. The use of natural gas does not require any modification of the gas meter or electricity contract.










Sources:
ENEA Publication – Department of Energy – pamphlet, “Heat pumps”
Robur SpA technical documentation – gas absorption heat pumps

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