Last edited 17 Oct 2016

Refrigerants in buildings


[edit] Introduction

Refrigerants are used in buildings:

They provide cooling in a process that is essentially the same as that used in domestic fridges, based on either compression or absorption:

  • In compression systems, a liquid refrigerant with a low boiling point absorbs heat from the body that is being cooled and boils in an evaporator to form a gas. The resulting gas is then compressed, which increases its temperature further. The gas is then condensed, releasing its latent heat which is rejected. The process then repeats.
  • Absorption refrigeration works on a similar basis, with a refrigerant that boils at low temperature and pressure, however, in this case, the refrigerant gas is then absorbed in a solution which is then heated in a ‘generator’ so that the refrigerant evaporates again, but this time at a higher pressure and temperature. The gas is then condensed, releasing its latent heat which is rejected. The process then repeats. See absorption refrigeration for more information.

Typically in heating, ventilation and air conditioning systems, chiller units use refrigerants to produce chilled water that is piped to air handling units (or fan coil units) where it is used to cool the air that ventilates the building. The ‘warmed’ water is then returned to the chiller unit to be re-cooled.

An alternative system supplies the refrigerant itself (rather than chilled water) to terminal units supplying different thermal zones. These ‘variable refrigerant flow’ (VRF) systems use a single external condensing unit and multiple internal evaporators and can be more efficient, more compact and offer greater flexibility than other HVAC systems.

The exact opposite of the refrigeration process can be achieved by heat pumps, which use refrigerants, but reverse the cycle so that heat is supplied to the building rather than cooling. Some systems are reversible, able to supple either heat or cooling.

[edit] CFC’s and HCFC’s

Some refrigerants have both ozone depletion potential (ODP) and global warming potential (GWP), and as a consequence refrigerants such as CFC’s (chlorofluorocarbons) are banned.

New equipment using HCFCs (hydrochlorofluorocarbons such as R22 and R408A) was banned in 2001 (2004 for small systems), and the use of virgin HCFC's was banned in 2010, when it also became illegal to manufacture HCFC refrigerants or for suppliers to keep them in stock.

From January 1st 2015 the use of HCFC’s was prohibited in any form, even for maintenance.

Refrigerants such as HFC's (hydrofluorocarbons) can often by used as drop-in replacements for HCFC’s however they can lead to a drop in efficiency and so may need to be supplemented with additional compressor and/or heat exchanger capacity. Badly maintained equipment or old HCFC systems may not lend themselves to conversion and could need complete replacement

[edit] F gases

Fluorinated gases (F gases) are not ozone depleting and they are often used as substitutes for CFC’s and HCFC’s. However they are powerful greenhouse gases (up to 20,000 times more powerful than CO2) and are listed as part of the Kyoto Protocol basket of greenhouse gases. As emissions of F gases increase, so their use is coming under greater scrutiny.

Hydrofluorocarbons (HFCs) are F gases. HFC’s are commonly used in buildings and include refrigerants such as R134a, R404A, R407C and R507C.

Other F gases include perfluorocarbons (PFCs) and sulphur hexafluoride (SF6).

On 15 October 2016 it was announced that 170 countries in Kigali, Rwanda, had agreed that all HFC’s should be phased out through an amendment to the Montreal Protocol. See HFC phase out for more information.

[edit] Alternatives

Other refrigerants include:

  • Ammonia (R717). A so-called ‘natural’ refrigerant, commonly used in absorption refrigeration. Ammonia is not an ozone depleting gas or a global warming gas. However it is flammable and toxic so additional precautions are necessary in design and use.
  • Non-halogenated hydrocarbons such as propane and butane (such as R290, R600a and R1270). These are ‘natural’ and not ozone depleting but do have some global warming potential and are flammable, so additional precautions are necessary in design and use.
  • Carbon dioxide (R744). This is ‘natural’ and not ozone depleting but does have some global warming potential.
  • Hydrofluoro olefin (HFO) is a refrigerant but is most commonly used in automotive air conditioning systems.
  • Water and air.

[edit] Leakage

It should be noted that refrigerants only have a global warming effect if they are allowed to leak to the atmosphere. This is more likely in ‘engineered’ systems than modular systems that have been hermetically sealed in the factory. Careful design, installation and maintenance can also help reduce leakage, and diagnostic and prognostic monitoring systems are available that can help detect or even predict leaks.

[edit] Find out more

[edit] Related articles on Designing Buildings Wiki

[edit] External references