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

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

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.

 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.