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ENERGY: Using Heat Pump Technology to Cut Energy Costs

 





Recent Gauteng Business News

The latest technology to move from the engineering design table to the residential consumer market in energy efficiency and the green sector is the heat pump, which helps to cut energy costs. Written by SESSA (Sustainable Energy Society of Southern Africa), this article explains the technology and the impact it can have on domestic energy consumption and savings.


If asked how we get hot water in our homes, most of us would reply ‘the geyser’, and we’d not be 100% incorrect. A geyser, however, is simply an insulated hot water tank. The water within the geyser can be warmed in three ways: using an electrical resistance element, using a heat pump, or using a solar collector.

What most of us mean, therefore, when answering the question, is that our hot water is warmed by an element. The purpose of this article is to compare two of these technologies – the electrical resistance element and the heat pump.

The major difference is that an element uses electricity to create heat, while a heat pump uses electricity to move heat. All things being equal, it is far more efficient to move heat (heat pump technology), than to create heat (element technology), which is why investing in a heat pump makes financial sense.

Comparing the Two Technologies to See How They Cut Energy Costs


An electrical resistance element is very basic technology. When it is fitted inside a geyser, the heat it generates is transferred from the element to the water. It is also very light (about 300g), relatively cheap (±R150) and readily available. All these factors mean that, should it stop working, it can be easily repaired by just one person, typically a plumber, with minimum fuss. However, it is expensive to run.

By contrast, a heat pump – or more correctly, a heat pump system – uses smart engineering to warm water by transferring heat from the air into the water in the geyser. This is achieved by moving a refrigerant in a continuous cycle that boils and condenses it. Boiling the refrigerant absorbs the heat from the air, condensing it transfers the heat into the water. This is possible because the refrigerant has a lower boiling point than air.

In much the same way as the parts of an air conditioner are contained in a ‘box’, so too are the parts of a heat pump. These include an electric fan, a small electric gas compressor and a small electric water pump; an evaporator, an expansion valve and a heat exchanger, and of course, the refrigerant that changes from liquid to gas and back again in a continuous cycle. This refrigerant has a far lower boiling temperature than water, which means that it changes from a liquid into a gas far more readily than water would making it a far more efficient heat energy ‘collector’. The closer the heat pump to the geyser, the more effective the system.

For many people, knowing just those facts is sufficient. For those who want to know how the heat pump functions in greater detail, this is how the continuous cycle works:
• The cold refrigerant liquid and gas mixture enters the evaporator.
• The air blown by the fan over the evaporator causes the refrigerant to gain heat energy from the air.
• This boils the refrigerant, changing it from liquid to gas, and continues to add heat to the gas.
• The gas absorbs heat from the air and is compressed, a process which raises its temperature further.
• The refrigerant – now in a hot, high-pressure gaseous form – is then moved through the system to the heat exchanger.
• Here, the water absorbs the heat energy, and the refrigerant loses heat energy.
• The water pump feeds cold water into one side of the heat exchanger, and the water is heated typically by about 5°C, to return to the geyser.
• Now being cooler, the refrigerant becomes liquid again, though still at a high pressure.
• The high pressure liquid passes through the expansion valve, changing to a low temperature, low pressure liquid and vapour mixture.

Why the Heat Pump Can Cut Energy Costs


Because a heat pump is a system and weights about 60kgs, installations and maintenance is more complex than for an electrical resistive element. It can, however, be installed by a team comprising of an electrician and a plumber; repairs are typically carried out by an air-conditioning technician.

A heat pump is installed by an electrician and a plumber. It is repaired by an air conditioning technician. It also costs around R15 000 before the rebate currently being offered by Eskom. However, because it is so efficient, it can shave up to 70% off the costs of heating water using an element.

If you consider that electricity costs are expected to rise at above inflation rates until 2021, a heat pump can prove a wise investment. For example, heating 200 litres of water per day costs just under R14 per day using an element, and less than R5 per day using a heat pump.

There are also the Eskom rebates, based on the size of the heat pump purchased, to factor into the equation (http://www.eskomidm.co.za/heat-pumps):

Finally, South Africa’s building regulations will, from 2012, demand sustainable energy systems be incorporated into all new residential buildings. In terms of SANS 10400: “At least 50% by volume of the annual average hot water heating requirement shall be provided by means other than electrical resistance heating including, but not limited to solar heating, heat pumps, heat recovery from other systems or processes and renewable combustible fuel.”


In summary, a heat pump is a well engineered compact system that heats water efficiently using electricity. Many of today’s heat pumps operate using environmentally-friendly refrigerants such as R407, R417 and R134, further enhancing the technology’s appeal as a ‘greener’ alternative to electricity-driven element-heated water.

All this suggests homeowners should consider replacing their convenient, but expensive, electrical resistance element system soon.


BOX: HEAT PUMP IN A NUTSHELL

Technical description – Air to water heat pump
Function – to heat domestic water for geysers
Reason to choose it over conventional geyser heating – it uses far less electricity to heat the water
Incentive to install a heat pump – Eskom pays a rebate of at least R3668 up until 31 March 2013
What does it look like‘ A small airconditioning unit (50 kg) mounted outside on a wall. Your geyser stays where it is. The unit and geyser are joined with water pipes.
Can it be installed inside, or in the roof‘ No. It needs a continuous source of ambient air.
Does it replace a geyser‘ No. It heats the geyser water. You still need the water stored in a geyser.
How much electricity does it save‘ A well installed and set heat pump can save 60% and more of your electrical element costs. The more you are using currently, the more you will save.
When does it save most‘ When the air outside is hot.
When does it save least‘ When the air outside is cold. If you can wait for the air outside to heat up, you will save more.

Is a heat pump better than solar water heating‘ Studies have shown that heat pumps are better suited for high hot water users, where the geyser may need reheating several times a day. Solar water heaters may be better suited to single family houses when the hot water usage is generally the same time each day. Ideally, we will use solar water heating, with the backup heating done with a heat pump.

Whichever investment you choose, you, your finances and your world will get a great return by helping you cut energy costs.


 
 
 
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