What is a High Temperature Heat Pump
A high-temperature heat pump (HTHP) is a heat pump capable of producing temperatures equal to or greater than those made by a boiler.
Most regular heat pumps, what we will call low-temperature heat pumps (LTHPs), heat water to 35℃ and 55℃. The lower the flow temperature, the more efficient their ratio of heat delivered to electricity used.
However, there are situations where this is not sufficient. It could be because older or larger homes need a greater heat output, or because the heat pump is being used for industrial processes that require much higher temperatures.
A HTHP can produce water at temperatures of 80℃ for residential use, or go well over 100℃ in heat pumps for industrial usage.
How Do High Temperature Heat Pumps Work?
High-temperature heat pumps take advantage of the properties of newer refrigerants or use more advanced systems to deliver greater temperature outputs. The two most commonly used setups for HTHPs work in one of two ways.
More Effective Refrigerants: Newer refrigerants can produce higher temperatures than the older ones they are replacing. Heat pumps with Propane (R290), CO2 (R744), or Isobutane (R600a) can make much hotter water than older refrigerants such as R32 or R410a.
Cascade System: A cascade HTHP uses a two-stage system with interconnected heat pumps. The first-stage heat pump is used to produce even hotter temperatures in the second stage than one heat pump could on its own.
Benefits of a High-Temperature Heat Pump
While LTHPs can provide domestic hot water, they require a specialised hot water cylinder and heat water slowly. With a high-temperature system, you can keep your existing cylinder and heat it quickly.
A high-temperature heat pump makes it much simpler to replace a boiler since it has a similar output. You are less likely to need to replace any radiators or other elements of the central heating system.
With a low-temperature heat pump, it can take many hours for any changes you make to the temperature controls for your home to take effect. Higher water temperatures can significantly improve this time.
HTHPs are more forgiving of homes with less effective insulation. This is because the higher temperature output isn’t as badly affected by heat loss through the building’s fabric.
An HTHP ensures greater home comfort by more easily providing heating temperatures that suit your desires, even in very cold weather.
High-temperature heat pumps can achieve efficiencies of up to 500%, greater than the 300-400% typical of regular heat pumps. They are also more efficient working with lower ambient temperatures in air source systems.
Who Needs a High-Temperature Heat Pump?
High-temperature heat pumps may be suitable for different types of residential, commercial and industrial buildings based on their main attribute of utilising hotter temperatures.
This makes them ideal for buildings where a LTHP is not sufficient. It may be due to the heat loss of the building, how far the heat needs to be distributed, or the scale of the area to be heated.
Retrofitting Older Homes
A high-temperature heat pump can be an excellent choice for much older homes compared to a regular heat pump. That is mainly because it is harder to make older homes suitable for low-temperature heat pumps.
Less Insulation Required: The water temperature being equivalent to what a boiler outputs means that
Works with Existing Radiators: The higher water flow temperature means you won’t need to get new large panel radiators, pipework, or a hot water cylinder.
Less Disruptive: The two points above mean that installing a heat pump requires less disruption to your life at home, since they require less work done on it.
Regulations May Prevent Work: Many older homes have legal protections that limit the work you can do on them. This may make it very difficult or impossible to improve their fabric to the point that a low-temperature heat pump would be viable.
Multi-Family Buildings
Buildings with multiple units that have larger heating needs sometimes use centralised heating systems. This could pose a problem for heat pumps due to how far the hot water travels across the entire building.
Large Space: A block of apartments has far more space to be heated, and uses more hot water than a single home.
Extensive Heating System: Multiple homes come with a very large network of pipes. This means there is a greater surface area through which heat can be lost.
Water Flow Temperature: A regular heat pump, with water at 35℃ – 55℃, may struggle to heat such a large space.
District Heating
District Heating is like having a centralised heating system for an apartment building, but on a larger scale, connecting multiple buildings. High-temperature industrial heat pumps can make use of waste heat from commercial and industrial buildings to power large areas.
Commercial & Industrial Processes
Commercial and industrial buildings have far greater heating needs due to their size. An HTHP is better suited to meeting this, as well as for industrial processes that require intense heat.
Types of High Temperature Heat Pumps
High-temperature cascade heat pumps use multiple interconnected heat pumps to produce higher temperatures than one heat pump would be able to achieve on its own.
They are primarily used where there is a very large gap between the temperature of the heat source and the temperature the heat pump needs to supply.
The two-stage process will typically use two different refrigerants, one of the first moderate temperature cycle and another for the second cycle. The exact refrigerants to be used will depend on the desired final temperature.
First Stage
The heat pump operates as regular, absorbing heat from an ambient source, and then further raising the temperature of the refrigerant by compressing it. Resulting in a moderate heat vapour.
Second Stage
In the second stage, the refrigerant from the first heat pump is used to evaporate the second stage refrigerant. This then goes through the same compression cycle to reach very high temperatures.
Carbon Dioxide (CO2) is capable of achieving very high temperature outputs when used as a refrigerant (R-744). This is due to the chemical and thermodynamic properties of CO2. A transcritical heat pump uses a gas cooler rather than a condenser and typically operates at very high pressures, which can make them more expensive due to the components required.
CO2 based heat pumps also have a very low Global Warming Potential compared to other synthetic refrigerants.
Propane (R290) is becoming more common as a refrigerant for residential heat pumps, replacing R32 as the refrigerant of choice. The advantage of R290 is that many single-stage heat pumps using it can reach water temperatures of up to 70℃.
This means that a standard heat pump can reach temperatures nearly equivalent to a boiler. However, for the highest COP it is still recommended that you use a lower flow temperature.
Cost of High Temperature Heat Pumps
High-temperature heat pumps are still an emerging technology in Ireland, so there is not a lot of information available on their pricing here. However, a high-temperature heat pump will be significantly more expensive than a low-temperature equivalent.
The cost of a HTHP can be inflated by the following factors:
- 1
Greater System Complexity: Systems such as a cascade heat pump are more complicated than a standard setup. They have more components involved in the multi-stage process.
- 2
Higher Quality Components: High temperature heat pumps often operate at much higher pressures, which need better components to avoid them wearing out too quickly.
- 3
Maintenance Costs: The higher temperatures and pressures involved in the operation of a HTHP can increase wear and tear, which will raise the maintenance costs for keeping them working in good condition.
Grants for High Temperature Heat Pumps
The SEAI offers up to €12,500 in grant funding for the installation of residential heat pumps in Ireland, with €6,500 for the heat pump system itself. The grant value is dependent on whether you have a house or an apartment.
Before getting a high temperature heat pump, you should consult with an installer to make sure that the system is approved by the SEAI as grant eligible.
Read more in our guide to grant funding for heat pumps.
Cost of High Temperature Heat Pumps
Yes, a high-temperature heat pump should be less expensive to run than an oil or gas boiler due to its very high efficiency, often up to 500%. This is compared to 90% – 94% efficiency in a new condensing boiler.
Yes, you can combine a high temperature heat pump with solar panels to generate the electricity that it uses to operate. This makes it even less expensive to run, and more environmentally friendly.
