Unsupported browser

For a better experience please update your browser to its latest version.

Your browser appears to have cookies disabled. For the best experience of this website, please enable cookies in your browser

We'll assume we have your consent to use cookies, for example so you won't need to log in each time you visit our site.
Learn more

An inspector cools

The UK needs to train an army of air conditioning inspectors to meet the demands of the Energy Performance of Buildings Directive. A dubious Mike Creamer reports back from the new front line

Most air conditioned public and commercial buildings in the country are now subject to mandatory inspections under the Energy Performance of Buildings Directive. This is going to be a colossal task, requiring an army of inspectors fully conversant with the often complex relationship between plant performance, energy consumption, equipment design/maintenance, and of course occupancy comfort.

As someone with much experience in this area, I recently decided to undertake the necessary steps to become an air conditioning inspector. My first step, along with 30 or so others, was to attend a one-day seminar to learn all about an inspector’s essential duties.

In a nutshell, the main purpose of an inspection is to produce a reasonably accurate evaluation of a building’s air conditioning systems, with a view to issuing a certificate describing the energy efficiency of the building.

As part of this, the inspector must determine the building cooling load, match it against the system’s cooling capacity, and report on the adequacy, or otherwise, of such equipment to meet the cooling load.

As the day of the course approached, I looked forward to a detailed briefing on how inspectors should go about their task. I anticipated they would be taught how to connect temperature and pressure sensors (or gauges), and current clamps, to different types of systems, in order to determine their current operating condition, efficiency, and so on. With recent developments in technology, it is now possible accurately to determine system cooling and heating capacity, heat of rejection, power input, and isentropic efficiency, COP, running condition, refrigerant charge status and many other parameters, in order to determine the operational efficiency of systems type running on any refrigerant.

I would then be able to use a CIBSE-based heat gain/heat loss calculation software package to accurately determine building load, matching this against the measured equipment cooling capacity in order to complete my task. The result would be a clear and accurate report for the building owner.

I was in for a major disappointment.

It turns out that the new breed of air conditioning inspector is not required to go to any such lengths to fulfil the task. Instead, guided by TM44, they are advised to rely on indirect data, such as commissioning records (if they exist), nameplate data (where still intact), manufacturer’s literature (if available) and other subjective physical observations/measurements in order to arrive at an assessment.

It strikes me that perhaps the reason for this approach is to allow inspectors to come up with an opinion without detailed knowledge and experience of air conditioning systems, and without the essential tools – or training – one might reasonably expect for such work.

Anyone familiar with the basics of refrigeration theory knows that the cooling capacity, power input, and COP/efficiency of refrigeration and air conditioning systems varies greatly with ambient temperature and the thermal load at the evaporator. This is why manufacturers show the performance and power input of their equipment over a wide range of specific condition combinations.

As a result, even with the best instrumentation available, it is not possible to determine the true peak cooling capacity of an air conditioning or refrigeration system unless the test is conducted at the design ambient temperature and under simultaneous full building load conditions – and only then with quite sophisticated equipment and a reasonable degree of knowledge.

As if this was not challenging enough, inspectors are required to determine capacity and efficiency, without even the basic refrigeration tools such as pressure gauges. Indeed, the inspector is also required to take running currents for compressors, fans, pumps, and so on. However, he would be ill-advised to do so if not electrically qualified, in order to work safely within high voltage three-phase electrical panels.

Where the peak building load is concerned, if this cannot be determined from documentation, “rules of thumb” are recommended as a means to achieving this. I am sorry to rock the boat here, but this is simply not good enough.

There are many factors to consider to derive a meaningful figure for load, as it is a function of solar movement, time lag, height correction, environmental mean radiant temperature calculations, dry bulb versus resultant calculations, latent gains, the associated psychometrics and numerous other factors. A so-called rule of thumb figure could wildly misrepresent the true and actual situation, and the whole basis of the calculation for the building could be, at best, inaccurate, and at worst completely misleading.

This is too big a subject for one column. I will return to this in the next instalment of… An inspector cools.