By Michael Young (Pr.Eng)

How climate change is causing HVAC systems to fail.

Also read:
Part 1
Part 2

Global warming was reported in the news about 30 years ago and since then, policies have changed and protocols have been implemented to help combat the effects of climate change.

Climate change is very real and many of us have experienced it first-hand with the milder winters and heatwaves during summer. The biggest problem that we face is drought, which has affected many parts of South Africa.

Increasing ambient temperatures also impose many different problems when it comes to the design of an HVAC systems and the type of technology that is implemented.

Engineers of the 21st century will have to consider the following moving forward:

How do existing HVAC systems that are older than 8 years cope with the new operating ambient conditions?

What are we going to change in the designs of new HVAC systems?

How are we going to tackle the problem of water shortages while still meeting the cooling requirements?

One issue with existing systems is the shutting down of an HVAC system on a ‘high pressure’ alarm. This problem occurs when insufficient heat is rejected from the condenser. When ambient temperatures rise, the temperature difference between the refrigerant and the ambient air decreases which then reduces the total heat of rejection (THR) of the condenser.

To solve this problem, either the ambient air condition must be lowered or the condenser capacity must be increased.

Decreasing the ambient temperature can be accomplish by implementing adiabatic cooling. Implementation of such a system however requires the use of water which doesn’t really help in addressing the water consumption problem.

Replacing the condenser involves a compatibility issue. Older refrigerant systems may still operate with R22 or R407C refrigerant. Most of the new direct expansion (DX) systems use R410A refrigerant.

It is still possible to get a system like this to work as unit setpoints and pressure transducers can be changed for different refrigerant gases. The R410A construction is also able to accommodate the higher operating pressure, so replacement of the condenser is still possible.

The final limiting problem is capital costs and looking further into the future. R22 gas is already illegal in Europe and one can expect R407C to follow. Replacing condensers can be an expensive process as refrigerant has to be reclaimed, condensers have to be rigged and there is no guarantee the indoor unit will last for another 5-10 years.

So, one needs to do an investigation to ask: “Is it really always worth it to replace an existing condensing unit when the indoor unit may break within the next 5-10 years? Will spares on these old units still be available, and is this exercise a good investment?”

Climate change is not only affecting our weather patterns, it is also causing new problems for systems that were designed on old ambient condition guidelines. So, what does climate change hold for the future designs of HVAC systems? Find out in next month’s publication of RACA Journal.

Wishing you a successful month ahead and chat soon.

Michael can be contacted on or 073 171 2311 for any questions or HVAC training needs.

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