There are several key points to consider when choosing the right air conditioning units to install. Steve Robinson explains.
The construction sector can make a huge contribution towards the Government's target to reduce energy-related carbon dioxide by 80 per cent by 2050.

This includes by retrofitting existing building stock, but because of the often individual nature of such projects - especially, for commercial properties - there can be uncertainties about the most environmentally efficient and effective air conditioning system to install.

New build projects, on the other hand, are a 'fresh' start, perhaps presenting better possibilities for good practice, design, construction, commissioning and, most importantly, efficient operation.

Nevertheless, there are many excellent examples of retrofit projects and it is interesting to look at exactly what features make them successful; along with identifying key factors to consider when choosing the right air conditioning system to install, which of course differs depending on the building.

In our 'green' quest, end users need to invest in the most appropriate technologies and use resources effectively; with specifiers and installers delivering robust retrofitting to ensure low energy demands and life cycle costs, whilst controlling risk levels for performance failure at the same time.

An important consideration when retrofitting a building - perhaps more so in larger developments - is to give end users the control to switch between cooling and heating.

Nowadays, the heat inside buildings is less likely to be released thanks to changes in building structures, such as the improvement of heat insulator performance and the use of double-pane windows. Cooling is required all through the year in the interior zone where there are lighting fixtures and other heat-generating equipment. In the perimeter zone, which is easily affected by ambient temperature and sunshine, either cooling or heating is required according to changes in the flow of heat.

Controlling the level of cooling and heating in the same building not only increases end user comfort, but also avoids unnecessary energy wastage, including overheating, overcooling and unattended operation.

Operating at part load

Another key consideration is to consider how good a unit's SEER is when operating at 25 per cent/50 per cent/75 per cent. A common mistake made my manufacturers of split and VRF air conditioning systems in the past has been to manufacture units that offer a great coefficient of performance (CoP) when run at full capacity.

However, what's actually more important is for the running costs to be effective when the systems are operated at part load, because the reality is that, if sized correctly, a unit will only run at maximum inverter frequency for a small duration of its operational time.

New legislation means that units must be manufactured with greater consideration of efficiency at part load when running at a lower inverter frequencies. Thus, it is key that specifiers and installers keep this important point in mind when opting for new units when retrofitting a new building.
VRF systems are increasingly used in retrofit projects and there are many good reasons for this. Modular and lightweight models offer great flexibility to the installer and end user, allowing for quicker or phased and extendable installation. VRF control systems can also be used to reduce interfacing cost by controlling and monitoring many of the additional mechanical and electrical systems in place in an existing building, for example, air handling units and lighting.
Many elements of a VRF system can also make redundant the need for costly additional heating and frost protection systems. VRF and split systems can be used to heat buildings, if sized correctly, when the ambient temperature is as low -20 deg C.

Additionally, frost protection via the recording of internal temperatures lower than a user selected set point, will force start heating to protect the building from frost.
VRF technology also offers features that protect end user safety and comfort.
Compressor rotation maintains the efficiency and increases life expectancy of VRF systems by spreading the duty of equivalent load to each compressor.

Backup operation prevents systems from coming to a complete stop in the unlikely event of one of the system's VRF outdoor units failing - the others connected on the same system can be operated continuously. And automatic judgement to check whether or not the refrigerant amount is sufficient in one refrigerant cycle minimises the risk associated with refrigerant leakage.

Finally, the right off-coil limitation can have significant impact on end user comfort. It allows us, as engineers, to use our skills in the corrective capacity selection of fan coils and air volumes, to completely eliminate the risk of cold draughts and reduce noise. This saves on costly isothermal grilles and ductwork attenuation, manufactured to mask the potential problem.

Short-term solution

While the price of a retrofit and keeping it as low as possible is often the top priority of many specifiers, installers and end users, this is only a short-term solution. We can't ignore the need for an energy-efficient, holistic approach to installations - keeping in mind many of the above points, which also enable great cost-savings in the long-term.

Ask your client to consider all of the additional areas your engineered solution can save in energy, end user comfort and control. Tendering for a building's best achievable long-term business fitness can ensure long-term sustainability.