By Michael Young

First thing to ask is, what is the LA?

I was browsing through a LinkedIn group the other day and a very interesting question caught my eye. The question posed was “Which is better, a DX type, or chilled water type of cooling system?”

The comments and replies posted within the group were very interesting as each person posted their viewpoint and opinion of which type of cooling technology was actually better. Some people stated that chilled water systems were more energy-efficient than DX systems while others stated that chilled water systems allowed for finer control of temperature within the space than DX systems.

Taking a few moments to think about the question before posting my reply, I suddenly realised that the answer is actually very involved and complex. Instead of rushing into a final answer, I decided to take some time to consider the entire process that is required to recommend a specific type of cooling technology.

The more I thought about it, the more I kept thinking about physics, mathematics and location. I kept thinking, heating and cooling load estimates, heat transfer and the second law of thermodynamics.

Now for most of us within the industry, we are always looking at cooling requirements, but many of us don’t realise that the location and application of a site can greatly influence the overall design of an HVAC system. So, what do I mean when I say that location and application (LA) influences the design of an HVAC system? Well let’s take Johannesburg and Dubai for example. Johannesburg is hot and dry while Dubai is extremely hot and humid in the summertime. During the winter season, Johannesburg is cold and dry, while Dubai is still fairly warm.

 Designing an HVAC system for both Johannesburg and Dubai would be very different with regard to the type of technology that is implemented as well as the heating and cooling load requirements.

Have you ever wondered why location of the site is the very first thing that needs to be selected when performing the heating and cooling load estimate? Let’s firstly understand the physics behind the workings of a heating and cooling load estimate program.

Should the air in Dubai be hot and humid for summer operations, our HVAC system would need to perform dehumidification and sensible cooling. Should the air be cold and dry in Johannesburg during the winter months, our HVAC system would need to provide sensible heating and humidification.

So, as we can see, the requirements of an HVAC system will differ by location. So how does application influence the requirements of an HVAC system? Well, if we designed an HVAC system to cool a general ward within a hospital, we would require the air to have a dry bulb temperature and humidity level that is comfortable for humans.

Should we now design an HVAC system for an operating theatre, the air would need to be purified with the use of HEPA filters and humidity levels would need to be very low.

So even though both systems are for a hospital type of application, the air conditioning requirements change according to the requirements of the application.

So how do all these factors influence the final result of the heating and cooling load estimate? Join us in the next issue where we will discuss how ambient temperature and humidity levels influence the fresh air load and behaviour of air.

Wishing you a successful month ahead and chat soon.