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An Air to Water Heat Pump can provide the ideal energy efficient hot water system for either domestic household use, or for larger Commercial applications.  In reality a Heat Pump provides slightly less energy savings when compared to a domestic solar water heater, but there are a number of other significant advantages associated with the use of an Air to Water Heat Pump.

One advantage of the Heat Pump is the aesthetic appearance that is gained by not having any solar panels or in some cases a storage tank as well on the roof of the building.  In some cases roof structures have to be reinforced when they are required to support the weight of a domestic sized solar storage tank that can weigh in excess of 400 kg.  The installation cost of an Air to Water Heat Pump is very simple compared to the installation cost of a solar water heater, and this significantly lower installation cost for the Heat Pumps should also be taken into consideration when assessing the overall installed cost of either product.

Another advantage of the Air to Water Heat Pump is the low energy draw from the electricity supply to operate the system, while at the same time producing an output of around 3 times more than the actual electrical input, when operated in average ambient temperatures of 20 degrees Celsius.  In reality this is a saving in energy of approximately 75% when compared to traditional electric water heaters.  In Regions where the average ambient temperature is higher than 20 degrees Celsius the actual energy savings can be higher due to the extra efficiency that is gained in these conditions.  There is also no need for sunlight because an Air to Water Heat Pump gains its free energy from the ambient air.    Contrary to popular belief, a solar water heater does requires back-up electrical energy to operate the booster element during periods of inclement weather, low radiation periods, and at night time when there is a need to supply hot water during those times.  The annual back-up energy needed to ensure solar water heaters provide an uninterrupted supply of hot water regardless of weather conditions, or if hot water is needed during the evening period, is similar to what is expended annually for a Heat Pump to drive the evaporator fan and compressor when comparing similar volumes of hot water delivery.   A domestic sized Heat Pump could, if required, operate from Photovoltaic (PV) solar cell system due to the low energy input needed compared to the actual output that is delivered in the form of hot water.

By Mel Peatey.

Look for my next post that explains the advantages of Heat Pumps in the larger Commercial installations.

There are a number of advantages associated with installing an Air to Water Heat Pump for domestic as well as commercial applications, and I will endeavor to explain those advantages in this blog.
Some people are uncomfortable with the fact that Air to Water Heat Pumps use electricity for their operation.   Whilst this is correct, it is important to understand how much electricity is consumed to operate the Air to Water Heat Pump as well as understanding exactly what the electricity is expended on for the operation of the Air to Water Heat Pump.  A small amount of electricity is consumed to run the compressor and fan components in an Air to Water Heat Pump.  The amount is usually somewhere between 70% and 80% less than what would be consumed to heat a similar volume of hot water by a similar temperature rise in a conventional well insulated electric storage water heater.   The heating efficiency of an Air to Water Heat Pump is determined by the available ambient temperature of the air and the relative humidity of the region where the Air to Water Heat Pump is located.   Primarily, heat energy is extracted from the surrounding air by way of the evaporator that contains cool refrigerant gas where air is drawn through by the fan.  The vaporized gas is charged with considerably more heat energy when it then is compressed in the compressor which also uses electricity.  The super heated refrigerant vapor then dissipates the generated heat by way of a condenser or heat exchanger to the stored water that is required to be heated.

To obtain maximum benefit from the heat that is generated from the refrigerant gas in an Air to Water Heat Pump it is important to incorporate an efficient condenser of heat exchanger to transfer the generated heat to the water that is in the storage tank.  Some key elements of efficient transfer of heat are the surface area available for the heat transfer process and opposite directional flow between the water and the super heated refrigerant vapor.  Whilst Air to Water Heat Pumps are an ideal option for domestic applications, they are even more suited to Commercial applications, due to the Air to Water Heat Pumps ability to generate hot water efficiently 24 hours a day from the air.   Other energy efficient hot water appliances such as solar hot water systems are only able to generate free hot water during sunny periods, and definitely no solar contribution during the evening hours.   The other major benefit considerations that favor Air to Water Heat Pumps is the considerable reduction in installation space needed, as well as the significant reduction in installation costs, particularly when comparing installation costs associated with a solar hot water system.  For domestic applications the savings in energy use for an Air to Water Heat Pump when compared to a solar water heater is very similar over the course of a year, however, when selecting an Air to Water Heat Pump for Commercial applications no other hot water system can provide the same savings and installation cost savings as an Air to Water Heat Pump.

Posted By – Mel Peatey

One main problem that is encountered, particularly with project design of solar hot water systems, is that the systems are generally under designed.   This is sometimes done to give the end user the perception of a lower capital cost outlay, but in reality this practice can defeat the real purpose of using solar hot water systems.   In these circumstances end users will still pay a relatively high capital cost when compared to the outlay for a traditional electric hot water system, for something that provides hardly any saving benefit, due to the fact that the electric boosters in the solar systems are providing the majority of the energy input.  In reality it should be the other way around, where solar input should be the greater.

From a long term economics point of view, it is important to generate the maximum volume of hot water from each unit, but it is also important to achieve this, at the highest possible solar input, in order to minimise the amount of traditional electric back-up energy needed to operate the system effectively.

A typical good quality 300 Litre solar hot water system with two flat plate collector panels operating in a moderate to tropical climate, may produce (on average over a year) approximately 250 Litres of hot water every day from each 300 Litre system at 60 degrees Celsius, where the solar contribution (or solar input) of the system is around 80%.   This means that approximately 80% of all of the energy needed (over the year) to constantly produce 250 Litres at 60 degrees Celsius from each 300 litre system every day, would come free from the sun, and the other 20% would come from the electric backup element.    In terms of actual kWh of energy, this can be calculated mathematically as follows, assuming that the incoming temperature of the water is approximately 25°C and we want to increase the temperature to 60°C

kWh    = Lt. of water x Temp. Rise x Specific Heat of Water ÷ 3600

= 250 x 35 x 4.186 ÷ 3600

Total    = 10.17 kWh of energy for each 300 Lt. system per day.

Therefore, to produce 250 Litres of hot water per day (by electricity only) it would take 10.17 kWh.    If the numbers of Solar hot water systems are calculated correctly, by dividing the total litres of hot water requirement by 250 Lt. then you could expect to save 80% of that energy annually.    This would also give you sufficient storage capacity, and booster capacity to ensure constant hot water, even during any periods of prolonged inclement weather.

As a general rule of thumb, a Solar Contribution Factor (SCF) of between 80% to 85% is ideal for gaining the best economic benefits whilst ensuring that the system, or systems, do not “over perform” during periods of low usage and high radiation availability.

Over performance of the systems naturally causes overheating of the water in the storage tank.  This can trigger a release of built-up over temperature hot water from the pressure and temperature relief valve, therefore leaving the systems with very little hot water to use, generally at a time when it is most needed.   If this does occur, it usually happens at around the end of the day, and the storage tank can be left with very little (Solar generated) hot water for the evening period, and you are then back to using electric back-up.   Therefore, correct calculation and sizing is critical for the most economical installation.

Mel Peatey

Another method of reducing the effects of Global warming is to use Photovoltaic (PV) systems.  However, these products use a totally different type of technology than what is used for “thermal water heating” to convert radiation from the sun into useable electricity, through storage batteries and inverters.  Whilst most people are looking to “save” electricity by creating electricity from PV systems, these systems do not offer the same level of economic benefits as a solar or heat pump water heaters.   At present, most PV systems provide an efficiency level of approximately 17% which means they can convert approximately 17% of any available radiation into useable electrical energy.  On the other hand the technology used for solar water heater collector panels for instance, has been developed over many years with most systems on the market today offering efficiency levels of 70% and sometimes higher.  This in turn means solar thermal water heater panels can convert approximately 70% of any radiation that is available into heating energy for the water.

In a general domestic household situation, particularly in developed Nations, the energy needed to heat the water in a standard electric hot water system can represent between 40% and 60% of the total energy use of that household.  Solar or Heat Pump Water Heaters can save up to 80% of that energy which works out to be almost 40% to 50% of the total energy requirement of each household.  If this is then compared to an average saving of around 17% in energy use from Photovoltaic (PV) Systems, it is easy to see that at this point in time, solar or heat pump water heaters offer a better financial outcome for home owners.  However, in Commercial applications such as hotels, motels, larger restaurants, gymnasiums, and many other similar institutions, the sheer level (kW) of energy that can be saved by using large capacity commercial heat pump water heaters is enormous.  Some Governments are offering attractive rebate schemes to encourage commercial users to take advantage of these energy efficient appliances, and it will be these installations (particularly the commercial type) that will have a significant impact on Global Warming.

Global warming is a phenomenon that has been widely debated for a number of years now, and almost everyone has an opinion about it – some agree and others don’t agree.  Regardless of what any individual’s opinion may be, it is still worth considering for one moment the amount of pollutants that we as humans create and ultimately disperse into the atmosphere.   One of the largest sources of air pollutants contributing significantly to Global warming is gasoline and diesel engine motor vehicles.  This problem is emphasised even more in large cities all over the world mainly due to traffic congestion where motor vehicle engines are running for much longer periods, than they would if the traffic flow was better.  The amount of harmful carbon monoxide and carbon dioxide that is dispersed into the world atmosphere ever day is extreme to say the least.  To ensure that this situation changes, Governments must act quickly to participate themselves, and encourage private enterprise to develop alternative solutions that will allow the phasing out of the gasoline engine modes of transport.  Alternative suggestions could be battery powered, hybrid gasoline/battery powered, or hydrogen powered engines.  The general public also has a part to play by constantly lobbying politicians, and all communities working together.  

 Another simple method of addressing Global warming is by installing energy efficient products and equipment, such as energy efficient light bulbs and solar hot water systems, or heat pump hot water systems.   Heating water with renewable energy sources other than electricity or gas alone is something that can have a significant impact on Global warming.  The use of renewable energy sources such as the sun – for solar hot water systems or heat energy from the air – for heat pump hot water systems, savings of up to 80% of energy needed to heat the water can be achieved using renewable energy sources.  For a standard domestic household hot water system the reductions in carbon emissions gained by using a solar or heat pump hot water system can equate to the same emissions reduction as taking a small car off the road for one year.  Generally these types of technology are very cost effective and in recent years some National and even State Governments around the world have introduced solar hot water rebates to encourage people to purchase energy efficient hot water systems.   It is now important to raise awareness throughout the world in order to get as many people as possible to recognise and understand the impact of Global warming for the present, as well as for future generations.

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