No matter what your politics, green or mainstream, whether you believe global warming is fact or fiction, whether the summers seem to be drier and the winters wetter, the fact that the population of the United Kingdom has an ever growing desire for air conditioning cannot be denied!
Before we discuss technological ways to save the energy consumed by these room refrigerators we must first understand what air conditioning is and whether it, or comfort cooling, is actually required.
Air conditioning covers many areas but is typically ventilation using the heating, cooling and filtration of fresh air whilst controlling the humidity at the same time. This can be extended further to Close Control Air Conditioning where, as the name suggests, air humidity, temperature and cleanliness are finely controlled and, more often than not, within tight parameters and within very fine tolerances. Whereas Comfort Cooling is at the other end of the spectrum; purely the supply of a refreshing cool air stream to aid comfort of an occupant but may add humidity to the room by the very nature of the cooling process.
How do you decide which one of the above you may require? The rule of thumb we usually use is if you have a draughty building with high ceilings and/or plenty of opening windows then even portable comfort cooling may be a more cost effective method and may be more suitable depending upon your needs. Areas with humidity or mild air pollution critical fixtures, or high quantities of public traffic are typical examples which are not suitable for comfort cooling and, therefore, air conditioning may be required. Whichever you choose I recommend an in-depth survey by a reputable company to fully determine your needs – it may show that you don’t actually need full air conditioning; this saves you all the installation, running and ongoing maintenance costs associated with your proposed installation.
So the first way to save energy is to consult a HVAC professional and see if air conditioning is actually required.
Nowadays, most modern buildings are designed in such a way that air conditioning is a pre-requisite and therefore the power consumption of the units needs to be considered in more ways than one. The easiest consumption to calculate is the load of the unit/units. Each unit supplied should come with an EPL, Energy Performance Label, which should show you the running consumption of the unit and its comparative efficiency. It is quite simple to add these loads to calculate the effect of the added air conditioning circuits. However, what is not so easy to calculate is the Power Factor effect of the units. With many units installed in a building, all capable of being switched on maximum and left with no ‘automatic off button’ you could severely affect your overall Power Factor.
Power Factor is too large a topic to be included in an air conditioning feature but it should be mentioned that buildings using a 3-phase supply are charged for the following power consumption:
Charged = (VxAx1.73) / 1000 where V = Volts and A = Amps.
However, in reality, they only use the following power:
Used = (VxAx1.73)xPF / 1000Â where PF is Power Factor
Therefore, if you install air conditioning you need to limit this Power Factor issue by either having PFC (Power Factor Correction) or occupancy control to cut out the operation of the units when the rooms are not occupied.
Occupancy detectors are a very efficient control for air conditioning, if you use a good quality unit and switch through a contactor or relay. However people normally only consider occupancy detectors for lighting circuits, which can often be much lower loads than the air conditioning circuits. I normally recommend switching through a product like our ‘BLS’ which can detect seated people typing on a keyboard from over three metres away; ensuring the air conditioning is only on when there is someone there to benefit from it!
Another scenario we were recently asked to design around was where the air conditioning power in over 1,000 bedrooms of a prestigious hotel, was to be controlled by detecting occupancy, but without the visibility of the sensors. By utilising HF3360 microwave sensors behind the ceilings we achieved fully concealed occupancy control, ensuring the guests could not leave the air conditioning on all night whilst they were out seeing the sights of London!
The above methods can both be adopted for localised air conditioning, where the system is not centralised through shared risers, heaters, coolers, filtration, etc. With the cooling speeds of modern localised air conditioning units you can achieve considerable savings and provide speedy environmental improvements at a relatively low additional cost.
However, when you are using a centrally based system a simple occupancy switch and a contactor will not suffice. Another installation we were involved with benefited from a different type of detector and had the added benefit of improving air quality and saving large amounts of energy at the same time.
In this particular installation we had a central system with several risers. Each riser had a ramped fan to draw the air through them and each room had a localised fan to assist the air extraction. All the localised fans were on when the room key card was left in the card slot – you know the type where your business card works just as well! We controlled the fan through an occupancy detector, saving 35 Watts for each room that was unoccupied. In the risers and in all the large meeting rooms, banqueting suites and ballrooms, etc, we placed occupancy detectors and Aircheck Control CO2 detectors. The CO2 detectors accurately detect the amount of CO2 in the atmosphere and translated this back to the central BMS. This allowed the BMS to determine if the fresh air intake actually needed to be left at its default setting of 15% or increased during high occupation; however, most of the time it was reduced to around 5%.
The Chief Engineer claimed that this reduction from 15% to 5% fresh air intake saved approximately 40% of the air conditioning running costs – plus, as the air handling was now reduced because of accurate air quality and room detection, the riser motors could be ramped down further, saving yet more energy and reducing long term wear and tear, thereby decreasing maintenance costs.
The Aircheck sensors can benefit everyone – you don’t need to have air conditioning. By using the Signal version of the product, you obtain an audible beep when air quality is substandard and a green LED is replaced by an amber one. When air quality decreases further, an additional audible beep is heard and the amber LED is exchanged for a red one, indicating poor air quality. This is required because humans are incapable of determining the need for fresh air – we just feel stuffy, tired, confused, etc, when we get too much CO2!
So how do we save energy with air conditioning? Well the first and last element show that air conditioning may not actually be required in the first place and by using the Aircheck Signal you can observe whether or not you have good air quality. Secondly, you can use occupancy detectors to avoid leaving unnecessary units on without anyone being there to benefit from them. And, finally, you could save more energy than you thought possible by incorporating Aircheck Control sensors into your BMS.