Heat Pumps -a multiplier for free energy
Heat pumps are thermodynamic Heating systems that extract energy out of a heat source which is freely available in abundance (eg. Out door air, lake water, solar etc.), and multiply the energy used in the process up to five fold. The enhanced energy out put is utilized in domestic and commercial space heating and also in DHW systems.
How does it work?
A heat pump is primarily a mechanical system combined with an electrical control system. The basic components include:
- Refrigeration compressor,
- A refrigerant as a Heat transfer medium
- A condenser for the compressed refrigerant gas ( a Heat exchanger)
- An evaporator ( another heat exchanger)
- Expansion Valve (A throttling device for the liquefied refrigerant) installed in line before the evaporator.
- Electrical system components such as controls, blowers, sensors etc.
What you would notice is that the system is very similar to the domestic air conditioner or the refrigerator in your home. This is very much so that the type of heat pumps known as air to air heat pump do function in the hot summers as an air conditioner with the help of a process reversing valve.
Investigate first
To investigate the feasibility of your application by a heat pump three basic points may be considered.
- Heat Requirement: It is the prime requirement in your consideration. A technically sound heat load calculation of your home may be carried out using modern software such as Carrier E-20-ii.
- Temperatures: The temperatures desired at points of usage must known.
- Availability of waste or free heat sources that can be easily tapped close at hand.
- Availability of supplementary heat sources and their advantages or disadvantages.
The Heat sources that may be used in heat pumps
- Outdoor air (Air to Air or Air source design)
The main advantage of outdoor air is that it is always there. However there are a few disadvantages as well. For eg.
When you need it’s heat most (say in the winter) it is at it’s coldest.
The evaporator in the outdoors needs to be defrosted often. The source of heat here may be electrical most of the time and occasionally hot gas.
The temperature out door being very low, a larger quantity of energy is spent for this function.
If the heat pump is designed for the entire building load the dimensions will be huge.
The annual Coefficient of Performance (COP) is low.
- Ground Heat
Surface Earth Heat may be utilized with very simple equipment but requires a suitable soil. Easily workable clay soil is the best in this aspect. In this system, plastic (eg. polybutylene) tubing is buried at a depth of 0.6 to 1.5 m in soil. Glycol or other brines are pumped in pipes directly connected to the heat pump. The temperature of the glycol is selected generally in the range of -2 0C to -10 0C. Surface ground heat in combination with outside air frequently provide lower capital cost and higher COP factors.
Deep ground heat too may be utilized with relatively simple equipment. Water may be pumped from a drilled well which after passing through the heat pump and transferring the heat energy to the refrigerant is returned back to the well. Of course heat energy must be available to the water in the well through water table or other sources.
(This is in fact similar to geothermal heat extraction).
- Ground Water Table
The temperature (and also the quality) of ground water varies with the depth and the location from which it is obtained. In general it may be considered about 8 0 C.
- Lakes and Streams
Most lakes and streams have low temperatures during the winter. But still it may be used as a heat source in direct as well as indirect methods. Direct methods are applicable when the water temperature is in excess of +5 0C.This produces a leaving cooled medium temperature of +2 0C.The maximum flow though the heat pump however should be ensured for trouble free performance.
Other sources of heat such as Industrial waste water and excess process heat, Condenser heat from refrigeration systems, clean or treated community waste water, exhaust air etc some other heat sources which are being utilized for operating heat pumps.
Grants available from SEAI
Grants are available from Sustainable Energy Authority of Ireland for retrofitting your existing heating systems with Air Source Heat Pumps which amounts up to Euro 2,000 per installation. For Geothermal systems this is Euro 2,000 upwards.
Apart from this you would save a packet on annual electricity or oil/gas bills, all the while cutting down on annual CO2 emissions of your household.
Interested in receiving more information on heat pumps (especially Air Source heat pumps) or installing one? Greentech.ie provides you free consultancy on all renewable energy systems, ways to save on your home energy bills and the government grants available for retrofits. Call them on Callsave 1890 245 345 for an appointment. It will cost you nothing.
