THERE IS LITTLE LOGIC BEHIND MANY CONTROL STRATEGIES FOR CHILLING, BY APPLYING SOME SIGNIFICANT SAVINGS COULD RESULT.

Now that the heating season is upon us again it might seem a strange time to be considering chillers, but how many chillers out there remain running despite a net heating demand? For that matter how many boilers continued running throughout the summer regardless of heating demand? Logically the two are in direct conflict with each other so running them at the same time must be illogical and you don’t need the Vulcan brain of Dr Spock from the Starship Enterprise to work that one out! Logic (and common sense) plays a significant part in improving the efficiency of building services, so why is it such a problem?

One of the greatest causes of energy inefficiency in buildings is the conflict between heating and chilling and it really shouldn’t be so, the good news is that it is not a difficult problem to overcome given a bit of focus and the result will lead to significant energy savings. As more and more buildings are having chillers installed the problem is growing and working against our efforts to reduce C02 and green house gas emissions.

To begin with if you are installing chillers make sure that they are not oversized, if they are not only will they cost more to install, they will cost much more to run over their life time. In fact when you install chillers (or if you already have them) make sure that you meter their electrical consumption so you know how much they are using, it is probably up to a third of your total electrical cost, but if you don’t know you will never be able to manage them properly.

There are a few simple opportunities for ensuring that your chillers are not going to run when they are not required;

Firstly, get control of your chillers (and boilers) onto your BEMS without this you will never know if the supply meets demand. Many chillers come with their own control sets and these will run them perfectly adequately for the provision of the right temperature, they will not however be able to optimise efficiency as they do not know what any of the rest of the building’s plant is up to.

Chillers operating 24/7 is normally a bad sign at any time of year, even in the very hot conditions of August 2003 it was not necessary to chill most buildings for a full 24 hours, when night time temperatures dropped is should have been possible to use a night purge, bringing in outside air to cool the building in readiness for the following day. The night purge should be standard in all situations, why pay for artificial chilling when it is available free from the great outdoors?

Make sure that your chillers are not inadvertently acting as heaters, this may sound strange, even illogical, but on more than a few occasions we have seen chillers producing flow temperatures above the outside air temperature, in effect the chillers are taking air in air at say 6 Deg C and “warming” it to a flow temperature set point of 10 Deg C to distribute throughout the building, why not just bring in the fresh air and distribute it through the air handlers, heating it with the boilers if required, it makes more sense and I think our friend Dr Spock would be more comfortable with this arrangement!

Ensure correct sequencing of chillers (and boilers), there is a direct correlation between the outside air temperature and the amount of chilling (or heating required) in most cases compensation is either non-existent or at best inexact. If you need water at say 5 deg C in the middle of summer (return 10 deg C) you won’t need water at 5 deg C on a colder day when return will be say 7 deg C, the solution is to make the sequencers target a chiller header temperature compensated to the outside air temperature.

Most chillers are also flow temperature sequenced, however it makes more sense and therefore is more logical to sequence than to a return temperature (the same is also true with boilers) this way you can ensure that there is a closer relationship between actual demand and supply or need for chilling.

So you needed hot water during summer and it comes from your main heating boilers, run the boilers, but if you have a four pipe system please ensure that the building heating circuits are not receiving any of the heat, this will only increase the load on the chillers and create a heating chilling conflict resulting in a waste of energy.

If in doubt about any of these elements challenge your contractors to prove to you that the plant that they are responsible for is operating as efficiently as it can, certainly getting it absolutely right, however logical, might be difficult, but unless the status quo is challenged the chances are that you will continue to waste energy on a large scale when it is easily within your grasp to do something about it, I am sure that this has a logical ring to it.