The fifth SAIRAC Tech Talk of the year was presented online on 20 July by Arshad Ali Khan, managing director of EHVAC, on the subject Global Warming and Changing HGAV & Buildings. Edited by Eamonn Ryan.
Change is inevitable. Climate change due to global warming has pushed the HVAC industry to new developments, adopting new equipment to minimise power consumption.
During the talk, Khan discussed how new technological and ideological changes are going to be the main drivers for the HVAC industry in the future. He touched on how global warming is affecting the building industry. He also touched on new, modular means of construction which will not be covered in this article.
Today my focus is on what we can do to make our HVAC projects more energy efficient, and what we can use as a natural resource – particularly ground water to make our water-cooled chillers more efficient.
An example of ways of reducing the global warming potential (GWP) is to use refrigerant ammonia, which gives a COP of more than four compared to a COP of three for standard air-cooled chillers in South Africa.
There are other options such as the geothermal HVAC which we don’t see employed much in South Africa. Another option is the absorption chiller technology for generator-based projects where we use gas engines to generate electricity, whereby the generator has an efficiency of 40% with the other 60% going into the air as thermal heat. If we can tap that using the absorption chillers, whereby we can use the jacket water as well as the exhaust from the generator to provide chilled water for a particular building or even a district – that is a future option for improving energy for HVAC.
Geothermal involves putting the coil beneath the ground and running the refrigerant through that to disperse the heat generated or collected from the building into groundwater. Geothermal heating is more efficient and cheaper than the alternatives, and consequently needs to be encouraged in larger projects.
Ammonia is extensively used in the refrigeration sector where entire rooms are cooled using this technology. However, the old technology pumps ammonia from the condenser outside to the building up to the evaporator. This means that the ammonia has to be run into pipes that are made of stainless steel since ammonia is not copper-friendly. This makes the project expensive. On top of that, there is a hazard of ammonia leakage. But if you use an ammonia-based chiller, then the ammonia is confined to the chiller area only and glycol-based chilled water which at a sub-zero temperature can be pushed into the building safely as a win-win situation. The air-cooled ammonia chiller has a very good COP.
For bigger projects where multiple (two or three) megawatts of cooling are required for industrial process cooling, we offer water-cooled chillers which generally offer 4,5, or 6 COP. However, water-cooled chillers use a lot of water and electricity since their condenser is a cooling tower. There is a solution whereby we can replace the cooling towers with ground water. For instance, there was a big project done recently in Australia where a supercomputer is being cooled by groundwater. This is a reference point and encouragement for us to look into using groundwater and replacing the cooling tower.
For example, I’m currently working on a project in Johannesburg where we are using generators and an absorption chiller. If the condenser which is connected to the cooling tower can be replaced by a heat exchanger which is water-to-water, it gives better results. In this particular case, the cooling capex is nearly halved if we offer a ground water heat exchanger instead of a cooling tower. There is a 75% reduction in electricity consumption, and no water bill when using ground water heat exchanger.
Many companies are coming up with heat recovery fresh air units similar to fan coil units, but it has got two fans, so the inside air is not mixed with the outside air. That’s why it is called the fresh air heat recovery unit. It will reduce by two or three degrees Celsius the temperature which is coming from outside. It has a three-layer filtration system for 99.99% cleaning of particles, and an 80% heat load reduction with a simple retrofit for a payback period of less than three years.
We are minimising the use of air conditioning – but using less requires a lifestyle change. We are used to living in open houses and being outdoors. Rather than getting into open individual houses, more and more apartment blocks are coming up. One reason for this is to reduce the electrical expense and be economical.