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By Benjamin Brits
The split air conditioning system, today being more widely adopted in the residential market, is still a contender for several other applications too.
A split unit installed in a penthouse room. Image credit: © RACA Journal | Benjamin Brits
As with many of the larger HVAC technologies, split systems have also undergone many improvements and adaptations over the years. This has seen these units undergo changes in styles and aesthetics, efficiency, air distribution, filtration/air quality improvements, controls and connectivity.
As global temperatures have increased, and are set to rise further in future, the use of devices to control and condition indoor air in several applications will continue to hold greater importance. This situation, that can possibly soon become essential to occupant health, is also subject to multiple factors – of which many involve the inability to use large central systems or where accessibility is limited.
As numerous studies have shown, optimal indoor air quality, along with correct temperature and relative humidity conditions are all critical elements in ensuring health, well-being, and performance of space occupants as they spend time indoors. Of course, the removal of pathogens from indoor spaces and the transmissibility of airborne diseases has also seen much attention and has become a major factor for space users as these impacts may be severe.
As we have seen over the course of this year, countries around the world have experienced all time high temperatures and of all of the factors involved, this is the major cause of illnesses leading to fatality. Experts have predicted that over the course of the next few years, more than 6-billion air conditioning units will be added to spaces and residences globally to combat temperature increases (and decreases).
Split units, technically referred to as “unitary HVAC equipment,” can provide cooling or heating only, or both cooling and heating. Cooling is most often supplied by a direct expansion (DX) system, while heating can be provided by several design types, including refrigerant gas, electric resistance elements, or supplemented by a heat pump. A heating function on unitary equipment is often not regarded – particularly in South Africa, but nevertheless, a mode that would be more necessary in certain geographical regions above others during seasonal fluctuations.
The major advantage of unitary systems is that, above the ease of installation of such units today, all components can be contained in one “cabinet” (eg: a rooftop unit) or they can be housed in two “cabinets” (eg: a split system). The indoor unit of a split system contains the space conditioning, filtration, and air movement components, and the outdoor unit houses the heat-rejection devices.
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Some other features of unitary systems may include any of the following:
- A smaller equipment footprint than central air handlers, chillers, or boilers.
- The ability to install heat rejection units outdoors, which reduces indoor space requirements (although depending on environmental and security factors this may open possible vulnerability to severe weather conditions or vandalism).
- One also has the ability to install heat rejection units in smaller indoor spaces (attics, ceiling voids, etc.) or on rooftops (here service accessibility/maintenance must be considered).
- Further, this system type may be used for installations with many individual spaces requiring individual control.
- New technology today also allows the use of multiple indoor units to a single outdoor unit – similar to the variable refrigerant flow technology, but on smaller scale.
- Certain models of unitary equipment have special coating to mitigate the effects of corrosive or chemical impacts.
- Unit finishes come in a wide variety of styles and colours to meet aesthetic appeal or requirement.
When considering the installation of unitary equipment, the engineer or contractor would, as with other HVAC systems, need to consider the application. Here a determination of what type of conditioning is required would be established as well as the service space, so for example cooling only is required for 12 hours a day to a 36m3 space – or five private offices located amongst an open plan setting or central closed off boardroom amidst spaces using natural ventilation, and so on.
Also, depending on location and thus humidity levels, as the natural refrigeration cycle “dries” the air – unitary equipment may be selected to combat humidity and address one of the most impactful elements in occupant comfort.
Unitary equipment, for the record, is not only about comfort cooling – they have several applications in a range of sectors that could include:
- Singular or remote spaces requiring control for comfort conditions of occupants
- Certain medical or examination rooms
- Data centres, server or interchange rooms
- Libraries and document storage rooms
- Wine cellars or enclosed specialised produce rooms
Air filtration and unitary units
Air conditioners don’t only perform the function of keeping occupants cool – they further play a major role, in both summer and winter months, by filtering the air. In summer conditions it is common for pollen and spores to be prevalent in air and during dry winter times dust is more common as well as other particulates such as dry skin flakes. New technology has enabled unitary equipment, also referred to “ductless ACs” to include the highest level of filtration as well as additives to control and eliminate even pathogens.
As the globe struggles with outdoor air quality, this has a direct impact on the air that enters buildings and so the traditional solution of introducing fresh air into a space to dilute contaminants is changing quickly as outside air quality deteriorates.
Every unitary air conditioner type uses a particular air filter to clean the air as it passes through the blower unit. Some use rudimentary filters that only catch large particulates all the way through to units that make use of high efficiency particulate arrestor (HEPA) filters.
Unitary units are considered more efficient at “cleaning air” dependant on their configuration, as air in and blown back out is situated at the same location.
A unitary unit installed in a wine and special spirit cooler room at an upmarket restaurant. Image credit: © RACA Journal | Benjamin Brits
Filters are usually placed on the return air of the unitary system. The air (that potentially contains contaminants) is trapped here at the filter. “Clean air” is then discharged into the space together with the cooled air.
The sizes of contaminants that exist in general air range from 0.01 microns to 10 000 microns. Virus, oil smoke, fumes and suspended impurities have sizes ranging from 0.01 to 1 micron. Mould, pollen, fog, dust, mists and ashes range from 1 to 100 microns. Dust emitted from heavy industry factories is about 100 to 10 000 microns, as some examples.
The ability of these filters to trap particles is measured by using the industry standard known as MERV or Minimum Efficiency Reporting Value. The values range from 1 to 20 and can trap particle sizes from 0.3 microns to 10 microns. The higher the value, the better the filter is able to trap smaller particles.
Standard office and home applications usually range from 1 to 12, with MERV 12 being able to trap particles from 1 to 3 microns. Highly specialised applications such as a clean room or a medical doctors facility would use MERV 16 to MERV 20 filters (where applicable).
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Types of common unitary filtration available
Plastic mesh filters are the most commonly installed at the return air of most indoor unit of unitary units. They trap larger particulates such as dust and hair. They are also the easiest for users to clean themselves and usually only involve using soapy water. Regular cleaning helps to ensure that the efficiency of the unit and hence energy savings, as well as clean air is continuous.
Electrostatic air filter technology is commonly placed in the return air of the unit where the air is subjected to high voltage up to 12kV between two plates. The ionised particles are then drawn to the grounded plates. The electronic circuit used to generate the voltage is usually embedded on the control printed circuit board or a separate module.
Carbon and adhesive filters are further other types available. The carbon type is made of activated carbon that is effective in removing odour causing gases and bacteria. Adhesive type is made of cotton and fibreglass material coated with adhesive oil or liquid which typically traps any particles.
Today another filter type is common in certain regions to address diesel particulates and odours where pollution is severe.
Technology advances
Some brands of unitary systems have developed several unique elements and features that may include fast cooling mode, sterilisation, air dispersion techniques and even motion sensors that tie into efficiency and effective operation automatically according to an occupant’s movement.
Other brands may include functions that quickly freeze the heat exchanger to create frost as well as self-cleaning cycles to mitigate the existence of microorganisms. Further wi-fi enabled units can be controlled via a smart device and provide various data sets such as operating conditions, maintenance reminders, efficiency and usage patterns.
The incorporation then of artificial intelligence (AI) can further optimise various modes by analysing a space condition and based on usage patterns, operate at an ideal level.
In future scenarios, the relationship between connectivity, AI and machine learning will offer users the ability to have intricate integration and with inclusion of smart devices such as phones and watches will enable unitary equipment to automatically be set to individual or group preferences that is not necessarily possible with other larger HVAC systems.
A dual split installation in a server room ensures redundancy mitigation. Image credit: © RACA Journal | Benjamin Brits
Maintenance and monitoring
Monitoring unitary HVAC systems is important to ensure ongoing and correct operation. In other words, to confirm that components are working as they should and that equipment is responding properly to control signals. For the contractor, discomfort, complaints, and noise can be indicators of unitary system performance issues.
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Best practice of course means adopting a preventive maintenance program which is critical in terms of function and efficiency. Keeping the unitary equipment in good condition results in a benefit of overall operations and maintenance costs and avoiding potential downtime, replacement, and shortened equipment lifespan.
Typically, a trained and authorised HVAC technician or mechanic performs the required equipment maintenance and repairs. Another benefit of unitary systems includes that any facility maintenance personnel or other approved on-site representatives can perform visual inspections and other routine checks, as well as document system issues.
As part of best practices, it is also important to keep a written log, preferably in electronic form of all services performed. This record should include findings from functions and diagnostics performed, corrective actions taken, equipment downtime, and other relevant issues noted. This will help identify recurring issues or systemic problems at each site.
In cases where the unitary HVAC equipment supports critical systems or building functions, additional monitoring of the equipment performance should be included to identify pending performance and condition degradation and even the onset of failure.
In South Africa, unitary HVAC equipment also forms part of the Pressure Equipment Regulation and as such requires that any maintenance or repairs be done through a qualified technician that is also required to have been trained in the safe handling of refrigerants.
Maintenance of unitary equipment today can easily be managed through a novel system available locally that includes the use of cleaning and refreshing chemicals to remove moulds and grime (commonly associated with HVAC systems) and special compressors. More information on this is available in prior issues of this journal. This system is not only a cleaning regime – it also includes performance monitoring and asset tracking.
Split AC matrix – SA
RACA Journal will continue to grow the matrix of all available split systems available in South Africa and as an example, the following are reference to models and certain specifications you can expect to find.
NOTE: The information contained in the listing, and future updated tables, is published as received from suppliers. Should the information provided be factually incorrect, this Journal platform cannot accept any liability on behalf on the provider. Should a discrepancy originate, please contact the distributor or agent directly.
Article Sources:
- General industry engagement
- ASHRAE
- Daikin
- LG
- Mitsubishi
- PNNL University
- Samsung
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