For most people a heat pump will hands down provide the best hot water experience, saving and return on investment.We covered this in detail in our “Solar versus Heat Pump Energy Savings”, “A Comparison of PV, Solar Thermal, Gas and Heat Pump water heating systems” and “PV and heat pumps goes hand in hand”. In this article we will give more of an executive summary.
The Key Benefits of a Heat Pump
- Guaranteed saving day and night, all year round.
A heat pump is not dependant on direct sunlight and uses energy extracted from the ambient air. Even at sub-zero temperatures ITS heat pumps can still produce 60°C water at close to half the cost of an electrical element. Solar water heaters can only heat the water while there is sunshine on the panel.
- Guaranteed peak electricity demand reduction.
An ITS-3.6HD heat pump draws about 1kW and can replace a 4kW electrical element. Therefore, you now have 3kW less load on your DB/PV system or generator. Solar water heating requires the element to help on days with less-than-ideal sunshine.
- Very tolerant to usage variation
A solar water heater is sized to heat the geyser once during a whole day of sunshine. If, for example, guest come over and uses all the hot water, the electrical element will have to re-heat the geyser. A correctly sized heat pump will typically take three hours to heat the geyser and so it can re-heat the geyser many times over in one day.
- Guaranteed greater than 60% energy saving on your water heating bill.
In real life operating conditions our heat pumps have an annual average COP of more than 3. In warm ambient conditions the COP can be more than 5 and in freezing ambient conditions it will be around 2. Most solar systems will give less than a 50% saving. Solar can provide a greater saving than a heat pump if sized correctly (correct size panel and double the size geyser that would be required for electrical heating), used correctly (bulk of the water either used in the morning or in the evening) and installed in a province with fairly constant solar irradiation throughout the year. In the Western Cape for example the solar irradiation levels are very low in winter and so you will have to rely heavily on electrical backup.
- Perfect match for solar electric (PV) systems.
An ITS-3.6HD heat pump only draws about 1kW and so it can easily be powered by most inverters and generators and therefore enables a complete off-grid solution. Sizing your PV system to power the geyser directly will require a bigger inverter and a lot more roof space for the extra PV panels that will be required. On rainy days you will need a big generator.
- Aesthetically pleasing.
A heat pump can be mounted out of sight. Solar needs a shade free north facing roof.
- No overheating problems.
The heat pump will heat the geyser to the desired temperature and then go into standby mode. Solar water heaters can overheat the geyser when for example everyone goes away for a weekend. This can be managed by correct installation material and pump control if it is a pumped solar system.
- Can be used in conjunction with solar heaters.
If you already have a solar water heater installed but you are finding that the electrical element is often needed to top up the temperature, you can replace the electrical element with a heat pump and use it to cover the shortfall from the solar panels. A hybrid system like this will result in the lowest possible consumption and the greenest system possible.
- Fully automated control – set and forget.
The heat pump onboard controller will monitor the geyser temperature and work only when it is required. There is no real need for timers etc to get the most out of a heat pump. On solar water heaters it is important to minimize the electrical element pre-heating in the morning before the sun comes up. Correct timer settings can play a significant role in maximizing the harvest from the sun.
- Environmentally friendly.
Extreme energy efficiency, with no greenhouse gas emissions. If a solar system is not properly sized (and very few in the country are), it will use more electricity than a heat pump resulting in more greenhouse gas emissions.
- Easy and less sensitive
Heat pumps can be wall mounted or floor mounted and just need a power cable and two pipes to the geyser. Solar installations are often on roofs and required drilling holes through the roof for piping and mounting. Solar panels must be north facing at the correct angle and non-shaded. In pumped solar system reverse syphoningcan easily happen resulting in the geyser trying to heat the night sky after sundown.
A personal note: The above might sound like I am not a fan of solar water heating and that is not true. I love solar and have a seriously oversized solar system at my own house. I make use of flat plat solar collectors feeding into evacuated tube collectors connected to a 500L vertical tank specifically made for solar. However, even with all this equipment, I would be showering cold in the winter months here in Cape Town if it was not for my heat pump.
