There is no doubt there are many occasions where a unitary air conditioner is the ideal way to control comfort conditions within a small space, such as an office or hotel room. Usually the first option that is considered is a traditional split system but this isn’t always the most appropriate choice – often because the outdoor units are considered unsightly or do not comply with planning regulations.
In the past an alternative has been a packaged through-the-wall unit. However these old-style designs no longer satisfy prevailing energy regulations such as the Energy-related Products (ErP) Directive.
A more recent entry to the market is the condenserless twin-duct heat pump air conditioner with a packaged monobloc design and considerably better energy performance and lower noise levels compared to the traditional through-the-wall unit.
These packaged units certainly provide specifiers and installers with a viable alternative to split systems but it is important to be aware of the differences between units and select the one that best meets the needs of each project.
Clearly all of these units also share key characteristics. For example, they all have a monobloc design that avoids the need for an external condenser unit mounted outside the building. This is achieved by using a twin duct connection to the outside through an external wall so that the only elements visible from the outside are two small grilles. Ideally, these external grilles should only be open when the unit is operating and closed when it is turned off to help conserve energy and prevent ingress of dust, noise and insects.
Whilst these newer condenserless units are certainly much quieter than traditional through-the-wall units they can be a little noisier than split systems, so it is important to check the acoustic performance of any units that are being considered.
With new designs that incorporate high levels of acoustic insulation, as well as quieter compressors and fans, it is now possible to achieve noise levels as low as 32 dB at one metre on low speed (41 dB on high-speed). These are ideal for use in applications where noise levels are critical, such as in hotel rooms or libraries.
Energy performance is another important criterion and although condenserless units will not typically offer the same efficiency of the split system, the newest designs certainly come close. They are certainly able to provide Class A efficiency in line with new energy labelling regulations. Use of the latest generation of DC fans will also make a significant contribution to energy efficiency.
When considering the energy performance of a condenserless heat pump unit it is clearly important to consider the heating function as well as cooling. Indeed, in many of the applications of this condenserless technology, such as in hotel rooms, their main use will be for heating. So the ability to provide low carbon heating at ambient temperatures as low as -10°C is a significant benefit to the end customer.
In this respect another feature to look out for is constant warming of the drain pan when in heat pump mode to avoid the condensate drain icing up at low ambient temperatures.
With all unitary air conditioning, split or condenserless, control is important in ensuring the right balance of comfort and energy efficiency. It’s also important to bear in mind that the person controlling a unitary air conditioner is unlikely to be an air conditioning expert.
It is therefore important that the control interface with the air conditioner, either in the form of a touchscreen display on the unit or a remote controller, is easy to understand. In some circumstances, such as in a hotel, it may also be useful for the building owner to be able to pre-set the temperature set point and prevent or minimise any further adjustment by others to help save energy.
Whilst the visual impact on the exterior of the building might be a key reason for selecting a condenserless unit, the internal aesthetics must also be considered, in terms of appearance style and size. The mounting options can also prove to be very important in meeting the customer’s requirements.
For example, whilst high wall mounting is perfectly acceptable in many applications there are situations where low or medium height mounting is preferable. An obvious example is in a hotel room where there is no centralised heating and cooling system and through-the-wall units are located beneath windows. In such cases, a condenserless unit that can be mounted at low level provides an ideal opportunity for both new-build and retrofit projects.
Another useful design feature from the service engineer’s point of view is the ability to access all components from the front of the unit so that it is not necessary to remove the unit from the wall to carry out routine maintenance
Clearly there is no suggestion that these units will replace split and multi-split systems in all applications but there are many occasions where selecting the right condenserless, twin-duct unit is the most appropriate solution.