Reverse Cycle Heat Pump
Reverse Cycle Heat Pump
Most heat pumps are not a reverse cycle heat pump. They are either set up as heaters or as chillers. This means they can do one duty.
Swimming pool heat pumps are designed to do just that, heat the pool. There only duty is to make sure the pool temperature does not drop below a set point. However, on very hot days they do not prevent the pool or any body of water from over heating.
Same with chillers. Their job is to keep a body of water, such as a aquaculture tank, or a cold water plunge pool, cold. They do not stop the water getting too cold on a frost cold day.
However a reverse cycle heat pump is designed to do just that. Prevent the water getting too hot, or too cold. They are set to maintain a set point or dead band temperature range.
The other great thing about a reverse cycle system is that you can reduce the number of systems. You do not need separate heaters and chillers. So not only are they more efficient than gas for heating, you do not need to buy a separate chiller as well. 2 systems for the price of 1.
How do reverse cycle heat pump work?
A standard heat pump uses fans to draw air through its coil to gather heat from the environment (how heat pumps work). The coil acts like a heat sink and passes energy to the refrigerant that is then compressed, increasing this gathered heat, and rejecting the heat into the circulating water. It could be a swimming pool, aquaculture tank, hydroponic system or hot water loop.
A heat pump set up as a chiller travels in the reverse direction. This is done by acting as a heat sink for the water body instead of the air. Thus drawing heat from a circulating water body loop and rejecting it via the coil to the surrounding environment.
70% or more heat pumps are only set up as only heaters or only as chillers. With the balance being heater-chillers.
Consideration in selecting a reverse cycle heat pump?
A heat pump contains a refrigerant gas. Different gases have different properties. They are considered low, medium, high and combination range gasses. Different gasses fall under these banners.
- R404A is a low to medium refrigerant
- R410A is a low to medium refrigerant
- R407C is a medium to high refrigerant
- R134A is a medium to high refrigerant
- R32 is a medium refrigerant (Slightly Flammable)
This is important to know as you select the temperature range you are seeking. Toyesi uses R407C as its choice in refrigerant. Not only is it Ozone safe, it has a broad heat and chill range. Covering 10 Celsius to 45 Celsius comfortably. It also has the highest overall efficiency kW power to kW output in this temperature range. Reducing the size of equipment required.
Other considerations is that cooling process are not as efficient as heating processes. A heat pump is usually rated up to 30% higher in heating mode compared to chilling mode.
So it is important to do both a heat and chill load calculations on the water body’s requirements. Then selecting the largest load, whether it be the chilling load or heat load, and sizing the unit to suit.
Many people buy their heater-chiller (reverse cycle heat pump) based on the heat pump’s kW rating, not realising that this is usually the heating rating and not chilling rating. Thus the unit struggles to chill the water down.
Another important fact when selecting the right reverse cycle heat pump, even though they all have the ability to perform both the heating process, is that a reverse cycle heat pump comes in two main types.
Switch Cycle – Reverse Cycle Heat Pump
Switch Cycle – similar to an air conditioner, have a heat mode and a cool mode. But you have to choose which mode to operate. They do not perform in both modes at once.
This means you could use them in summer to cool water down, and in winter to warm water up. However, manual changing of the settings may be required through out the year if the mode change is required.
Out of the heater-chillers in the market most are designed this way.
True Reverse Cycle – Reverse Cycle Heat Pump
True Reverse Cycle heat pumps, like the Toyesi Heat Pump Range of heat pumps will perform both heating and cooling as required.
This means you can set up a desired temperature and the heat pump will automatically swap between heating and cooling in order to maintain the set temperature.
For example in aquaculture tank temperatures are often set for a whole year. The heat pump will alternate between heating and chilling mode to maintain this set temperature, usually with half or a few degree buffer.
Only a few brands of heat pumps handle this process well.
Other Critical Considerations
As mentioned before, chilling water is less efficient than heating within a heat pump, there are also design differences between a heat pump heater and a heat pump chiller.
This means that a heater chiller heat pump are dearer as they require both set ups in one.
But also many brands of reverse cycle heat pumps do not allow for the differences between the models, and thus often under perform in either mode or both modes. Systems with close kW ratings often have this issue. They will also tend to go out on fault more often as they have not been designed to properly handle both presses. A mistake made by manufacturers in an attempt to keep the costs down.
Some projects require the same temperature set point for heating and chilling mode. However, there are projects such as in aquaculture or process systems that may require seasonal or different heating and chilling set points.
Many heater-chillers cannot handle a wide range between these points. often a maximum of 5 to 10 degrees. This can be a refrigerant restriction, or equipment limitations. Care must be taken when selecting a system to ensure your projects range can be met.
Another thing you will notice(depending brand and set up) is that the COP of chilling ranges from 2 to 3, whilst the heating cycle is 4 to 6. This reflects the differences in processes and efficiencies between the two modes. The main reason for this, is that the refrigerants also pick up the heat of the compressor and motors inside the heat pump.
In heat mode this adds direct heating value and increases the output potential. However in cooling mode, this extra heat must also be rejected reducing the cooling output potential.
Toyesi’s Reverse Cycle Heat Pumps
Toyesi’s TET heat pump ranges are normally just heaters or chillers. However they can be designed as true reverse cycle heater chillers. Care is taken to allow for both processes to be built into the system.
Our heater chillers can also be designed to handle broad temperature ranges. For example we designed a system for a gold smelter to go from minus 10 Celsius to plus 50 Celsius. These systems are complex processes for a heat pump, and great care in engineering both heating and cooling sides into the system. This is not an easy feet as it is very easy to over size one side of the load, and under size the other.
All of Toyesi’s Trident Farm Fresh range of heat pumps for aquaculture & Horticulture come as true reverse cycle heater-chillers. This is important because many of these projects have very narrow critical temperatures to maintain.
Reverse Cycle Heat Pumps In Summary
Most heat pumps come as heaters or chillers only. A few come as heater-chillers or reverse cycle, however care must be taken in selecting the right type of system to meet the needs of the projects temperature range.
Toyesi has been building heat pumps for over 30 years, and not just a reseller of other brands. This means we have hands on experience in designing, building and recommending systems for all sorts of projects.
Sample collection of Toyesi & Trident Heat Pumps and Chillers..
If you want to now how Toyesi can help you and your water or pool heating project increase energy efficiency, reduce running costs or minimise your waste energy then give us a call.