Air Conditioning - Cool but Expensive

Why Apartment Air-Conditioning is a Mystery to Most Owners​

You may not be an Engineer but you’re probably quite smart.  Why then are you made to feel lacking  when an expert talks you about your expensive HVAC system.  With so much jargon even the title HVAC (Heating Ventilation and Air-Conditioning) is daunting.

Here is an easy to understand video from Gentech Motors that covers the basic concepts.

How Does It Work?

The Air Inside

• Simply put an air-conditioning unit cools down warm air in your apartment.
• The warm air is passed time and time again by a fan over a cooling coil that looks like your car radiator.
• Very cold fluid (about 3 degrees) passes through this coil.
• The cold air is called supply air and is delivered through ceiling outlets.
• The cooled apartment air is recycled back to the cooling coil and is called return air.
• Of course the fan moves the air  through a simple filter to remove dust.
• This recycling of air over the cooling coil continues until the space temperature is comfortable.
• Then the cooling machine (compressor) stops. This what the thermostat does.

 
The Compressor

• The compressor has a job to circulate the cooling fluid. Much like an air compressor moves air
• The fluid passes through a cooling(indoor) coil and a condenser (outdoor) coil.
• The outdoor unit also has a fan which again looks like your car radiator. This removes the heat that was pumped from the room (Heat Pump)
• The fluid (refrigerant) actually changes state like boiling water inside the cooling coil.
• Around 90% of the energy used by your HVAC unit is used by the compressor. The rest is used by the two fans​​

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Why Are They So Expensive to Operate – What Can I Do?
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1.  Set thermostat to 24 degrees and don’t touch. On hot days most units will only reduce temperature by around 10 degrees from outside temperature.
2. Both coils must be kept clean to prevent corroding. These heat exchangers are where all the energy is transferred and losses can be huge; Up 50% loss of thermal transfer capacity over 10 years. Energy saving  coil coatings are available to keep coils from corroding.
3. Of course, you should clean the filter so that the maximum air movement occurs. Losses can be up to 20%. Think of your car radiator being blocked.
4. Service your apartment unit regularly (at least annually) by a reputable technician and ask him what he did and condition of coils and compressor and refrigerant charge. Ask him what maintenance items can bring back cooling efficiency. He will probably talk about coil cleaning. Otherwise this will be ignored because its dirty work.
5. Like engine additives there are products available that improve internal heat exchange efficiency and remove oil fouling. That’s a film that develops on the inside and can cause inefficiency of up to 15%.  This also makes the compressor last longer and run for a shorter time
6. Back to air flow, make sure nothing restricts free air around the outdoor unit. Again think of your car radiator.

Typical HVAC System (OEH HVAC Optimisation Guide)

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​The Very Large Multi Residential  High Rise HVAC Systems
 
This is the serious end of energy saving and your servicing technicians must be highly skilled to even understand the engineering concepts of these systems. For a detailed technical reference we recommend downloading the HVAC Optimisation Guide from the NSW Office of Environment and Heritage (OEH). However, following is a basic overview.
 
Common HVAC Systems

1.  Large multi residential building do not have condensing units on balconies.
2. The condenser and compressors are generally built into one complete packaged unit. May be located in the ceiling or in a cupboard. This unit is your property.
3. The outdoor unit is replaced by a water heat exchanger this is inside you’re a/c unit. You will see water pipes connected to these systems.
4. The condenser water is pumped around the building by big expensive pumps. Water is cooled down inside a very large cooling tower. In larger building there can be multiple pumps and cooling towers.
5.  All of the heat from your home is transferred to the condenser water again like a radiator in your car. The cooling tower is simply  a massive radiator  Another less common system uses large Chillers which pump cold water (8 degrees) through to all apartments. Your apartment will only have a fan and coil assembly 

Save Energy on large Common Area HVAC Systems. Check with Your Technician or Building Manger;

1.  Ensure pumps only run when required. It is very common that these run 24 / 7 and use enormous energy. They should only run when  a call for cooling exists savings can be up to 60%
2.  Variable speed drives are easily fitted to fan motors on cooling towers and ventilation systems and are very cost effective savings around 20%.
3.  Optimisation of controls to make them work properly again can achieve savings up to 30%.
4.  Keep heat exchange surfaces clean and maintained where they exist, savings up to 15%
5.  Service and maintain plant to high order. Check for corrosion and fix it before very expensive rebuilds are required

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​And Finally ...
 
Whether you have a small split system or water cooled unit;

• Set controller so that you don’t over-cool your apartment. Even one degree lower makes a big difference to your energy bill
• Keep indoor and outdoor coils clean and stop corrosion. We can provide products for that.
• Have regular maintenance done and ask the technician to make clean coils & filters, check refrigerant levels. Anything to keep efficiency high.
• Additives are available to improve efficiency and extend life of your systems.

 
Note that your space heating systems are generally part of a HVAC unit and all of the above points apply.

For further review, try this explainer video from Genteq Motors.  You can also download the HVAC Optimisation Guide (PDF 110 Pages) from the NSW Office of Environment and Heritage (OEH).

Feel free to call us anytime 1300 782 761 for any advice, its free and we are good with dumb questions.
 
Tony Power
Energy Efficient AC Solutions 

Strata managers can now register buildings in the City of Sydney and in Melbourne for a fully funded electric vehicle recharge assessment. Registrations for Brisbane have closed. However, if you're interested in learning more contact Scott Witheridge on (02) 9977 1801 Read more about the program here.
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