Keeping a cool head about

Multi
Aesthetic and efficient air conditioning is provided by LG’s Artcool range of indoor units (facing page) combined with Multi V outdoor units.
Stuart Maddock considers what is available for designing an air conditioning system for a commercial/residential site and gives some pointers in what to look for in terms of products.There are two main types of air conditioning — unitary and field erected. The unitary products are complete manufacturers’ packages ready for simple site installation. ‘Field’ products are units arriving at site, usually in component format, which then need assembly in order to be commissioned and ready for use. This type of air conditioning system is the realm of VRF and Multi systems, where one outdoor unit is connected to multiple indoor units. The indoor units can be operated independently on and off, and the outdoor unit compensates by the compressor modulating the speed, thereby varying the refrigerant flow — hence the name Variable Refrigerant Flow (VRF). R410A With the introduction of refrigerant R410A, new scroll compressors were designed to maximise performance and efficiency. These systems are designed to be energy efficient, flexible and, most importantly, user friendly for the actual user. In many cases, fresh air must be supplied without increasing the energy consumption. The key to these products is the initial planning — not the usual ‘we need air conditioning in this room’ and fitting whatever is convenient or able to fit in the room. The indoor units are planned, with the building usage, along with the installation of the pipework. Correct pipe installation contributes to the overall effectiveness of the system. A multi system is similar to a VRF type system. The multi-system is usually in fixed numbers of indoor units. On smaller systems there could be, say, two to eight indoor units per outdoor unit. Such systems can only operate in cooling or heating mode; they cannot provide heating and cooling simultaneously. A 2-pipe VRF 2 system has the same limitations. It is only when the more sophisticated 3-pipe system is used that simultaneous heating and cooling is possible. A 3-pipe system gives a fully flexible installation that is often too complex for many buildings. A VRF system normally operates with around 16 units to one indoor unit. VRF systems are almost exclusively the realm of big commercial sites, the consulting engineer and the specialist mechanical and electrical contractor. Unitary products can be divided into two sub groups. These are single packaged units and split systems. Both types can be cooling-only or of the reversible type provide both heating and cooling. The unitary system — especially in view of last summer’s baking hot day after baking hot day — is the one that is coming to the fore in domestic sites. For several years many houses with large conservatories have used split air-conditioning systems to smooth out the hot and cold variants of what used to be our defined climatic seasons. The whole concept of domestic air conditioning seemed a non-starter in the temperate climate of the UK. But climate change and consumer choice form the basis of a huge potential upswing in the market for domestic air-conditioning systems. Packaged systems The air-conditioning single package, as the name says, is a complete manufactured package. Everything is ready for operation, including all wiring and internal piping to the evaporator and compressor. A package is fully charged with refrigerant, and the condensing coil is fully fitted and tested at the factory. On arrival to site, it is positioned and then needs connections to ductwork and main electrical supply and the installation of the controller. The advantage of this type of unitary air conditioning is the ease and speed of the installation. These compact units have the ability to serve many rooms within the building. The main disadvantage is the space required by the internal ductwork. Split systems The split system, as the name says, is supplied as two separate items. The indoor unit comprises the evaporator and control system. The outdoor unit comprises the compressor and condensing coil. These are supplied to site in sets, with the initial refrigerant charge for a defined distance in the outdoor unit. The installer completes the pipework and electrical wiring between the units. This equipment has a number of advantages — mainly the ease with which it can fit into existing buildings. The installer needs to regulate the refrigerant charge to correspond with the length of pipework. The wide range of equipment available can match the cooling and heating requirements of the various rooms within the building. The controllers supplied can control the room to the desired temperature with a quicker and more individual response than a central-station unit or package unit. The split system has the added advantage that in heating mode the room is heated economically, with 1 kW of electricity producing about 3 kW of heat. Split systems come in various formats. Outdoor units are always very similar in style; only the size and internal features change. Indoor units can be of various types — depending on application. They can be free-standing on the floor units or mounted on the wall at high or low level, or mounted in the ceiling with only the grille showing. All units are usually supplied with controls, either infra-red or direct hard wired to the unit. The positioning is important to ensure that cold and hot draughts are minimised and to ensure that the supply air is not short circuited back to the return air grille, reducing effective duty. There can be a disadvantage if care and attention is not given at the system design stage prior to installation. The length of pipework between outdoor and indoor units is an important consideration. The compressors are designed to pump the refrigerant to a specific distance with a specific duty so there is a loss of duty if the distance is too long. As the outdoor unit is normally positioned in an area where it is concealed, care has to be taken on the pipe run to minimise lengths. The maximum pipework separation for wall-mounted units is about 15 m and for ceiling units 50 m. Avoiding problems Great care, attention and skill needs to be given to installation. One of the most common problems is incorrect refrigerant charge. This is important as the products rely on an economical system for the expansion device (refrigerant control) called a capillary tube. This reduces pressure by reducing the flow of refrigerant through its length. If the system were overcharged, extra refrigerant would tend to fill the evaporator, and loss of performance would occur, as well as the compressor current being too high. Unitary air-conditioning products hold a major part of the whole marketplace — rightly so as they offer many advantages in reliability, ease of use and installation and overall price. There are other important factors to consider. One is noise of the equipment. This is often over looked until the equipment is installed, after which it can be a difficult problem to overcome. The noise can be due to structural vibration, or by reflected surfaces. The noise data that all manufactures give is usually in a ‘free field’. This means that there are no surfaces to bounce back the sound waves. This is often misunderstood, as the unit on site will rarely give the same figures as those given in the manufacturer’s data. There are many aspects of how noise can be amplified and transmitted. It is not by accident that musical instruments are made from wood! As with anything, a little homework goes a long way! Stuart Maddock is with LG Air Conditioning, LG House, 250 Bath Road, Slough, Berks SL1 4DX
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