Renewable changes to heat systems and heat pumps are crucial as our world faces an existential threat in the form of a climate emergency. Renewable methods of heating can help reduce greenhouse gases and, therefore the impact of global warming
The climate emergency makes itself felt across the globe with an alarming increase in the incidence of forest fires, devastating floods, relentless downpours, and other so-called ‘natural’ disasters.
The root cause of many of these disasters is the build-up of greenhouse gases (GHGs) over the last 50 years or so. GHGs – one of the most powerful of which is carbon dioxide – are known to trap the Sun’s heat near the Earth’s surface, causing the greenhouse effect, which, in turn, results in global warming.
Renewable methods of heating can help reduce GHGs (and therefore the impact of global warming), and that is why heat pumps – which run on electric power, increasingly fuelled by renewables – have emerged as a key tool in the global transition toward clean and reliable space and process heating.
How does a heat pump work?
A typical heat pump captures heat from outside and moves it into a building. It effectively operates like a fridge in reverse, using a refrigerant to absorb the heat that can be found naturally in the ground or air.
This refrigerant is compressed to increase its temperature, and the resulting heat can be used to raise the temperature of cold water. So, heat pumps move heat around rather than generating it. As their name suggests, reversible heat pumps do the same thing in reverse, thus generating cooling rather than heating.
Heat pumps for every application
Depending on the type of heat pump specified these versatile units can be employed for comfort air conditioning; cold store operation, heating air for drying (clothes, agricultural products, and so on); precooling fresh fruits, vegetables, or flowers; direct process fluid cooling in the chemical, pharmaceutical and food processing industry; heating water, and directly heating process fluids such as cleaning solutions in industrial washing machines.
Applications for heat pumps include offices, schools, restaurants, hotels, sports halls and health clubs, and healthcare facilities such as hospitals. Industrial applications include dairy, textile, pharmaceutical, food processing, cold stores and heat networks.
The benefits of heat pumps
Heat pumps offer an array of advantages. For example, they:
- Offer impressive energy efficiency.
- Can deliver an all-in-one heating and cooling system for both summer and winter comfort.
- Provide lower running costs than the alternatives.
- Reduce carbon emissions compared with fossil fuels.
- Are safer because there is no combustion involved in their use.
- Involve less maintenance (and therefore lower service costs) than a combustionbased heating system.
- Save space since there are no fuel storage requirements.
- Have a long lifespan.
Apart from being more environmentally friendly than fossil fuel-driven alternatives, heat pumps require less maintenance than other heating systems, they enhance safety because they don’t rely on combustion to generate heat so there are fewer risks associated with their use, they are more flexible because many can offer cooling as well as heating, and they have a long operational lifespan – 20 years or more is not uncommon.
The types of heat pump
There are essentially three types of heat pumps – air source heat pumps (also called air to water heat pumps), water source heat pumps (also called water to water heat pumps), ground source heat pumps.
Air source heat pumps
An air source heat pump (ASHP) can range from producing 5kW of heat to almost infinite size, subject to the space available and electrical supply. It uses a vapour compression cycle to absorb heat from the atmosphere and produce hot water at around 45°C. The next generation of these units will provide up to 90°C hot water production.
There are many refrigerant options available, including natural refrigerants such as carbon dioxide (CO2) which does not require F-Gas approval.
It is possible to have reversible (in other words, two-pipe operation) heat pumps, or polyvalent (four or six-pipe operation) heat pumps. More on these later.
An ASHP is highly effective as the first stage of a cascade system for direct hot water production and provides on-demand production. There are several important considerations when it comes to using an ASHP. For example:
- The defrost mode and space constraints, as well as air and compressor noise. ASHPs are noisier than boilers, the capital expenditure is higher, and maintenance requirements may also be greater.
- However, on the plus side, average efficiency levels across the year are higher with an ASHP, operating expenses are lower (particularly now the price of gas is increasing), and the technology is proven as a good alternative to gas boilers.
The simplest ASHP is a switchable two-pipe type, where the unit will provide chilled water for cooling in summer and hot water for heating in winter. This suits applications with a seasonal change-over or large ‘dead-band’ between cooling and heating temperatures.
The unit just needs a signal from the building management system (BMS) to tell it to operate in cooling or heating mode. The latest generation of ASHPs can provide up to 80°C hot water production at -4°C ambient.
Polyvalent Air Source Heat Pump
A polyvalent or four-pipe unit has three modes of operation to meet all the thermal requirements of the building – cooling only, heating only, and simultaneous production.
The unit is permanently connected to chilled water and hot water distribution pipework and, using built-in temperature sensors, will react to changes in the heating and cooling loads to meet the building demand. The BMS needs only to provide a run signal to the unit, the load control is handled by the on-board printed circuit board (PCB).
This type of unit provides the greatest flexibility in thermal production and can be setup to work a supplementary two-pipe unit to increase peak heating or cooling capacity, under the control of MTM supervisor unit.
A six-pipe polyvalent unit has the same chilled and hot water production as the four-pipe unit, but is fitted with an additional heat exchanger called a ‘desuperheater’ which uses the high temperature discharge gas from the compressor to provide between 10 and 15% of the cooling capacity as hot water in the region of 60 to 70°C.
This is not on-demand production of this higher water temperature, but merely a by-product of heating or cooling output.
Klima-Therm’s Air Source Heat Pumps:
Our range of ASHPs typically range from 5 to 700kW. High temperature options of up to 80°C are available and there are options for hydronic modules, low noise, and a host of accessories as well as different compressor technologies.
A variety of refrigerants are available from traditional HFCs to more modern low and ultra-low GWP alternatives.
Equipped with fixed speed or inverter-driven compressors, these reliable chillers with optional hydronic systems are available for quick despatch to suit your project deadline.
Hybrid heating & cooling in action
Kingston College
The first UK installation of Rhoss EXP hybrid cooling and heating technology from KlimaTherm was installed at the new Creative Industries Centre at Kingston College, London.
The innovative heat pump-based chiller was installed by Lowe & Oliver and specified by consultant Hamson JPA for its excellent energy efficiency and ability to provide simultaneous chilled water and hot water, linked to whole-building energy harvesting.
Northbrook College
Klima-Therm also supplied a hybrid heat pump chiller to Northbrook College’s West Durrington Campus, providing high efficiency, low carbon cooling and heating for a state-of-the-art refurbishment project.
The Rhoss EXP TXAETY 4200 heat pump chiller installed by Maybourne & Russell, was chosen for its ability to deliver low energy simultaneous chilled and hot water for use in air conditioning, heating, and domestic hot water supplies. The project achieved a Building Research Establishment Environmental Assessment Methodology (BREEAM) rating of Excellent.