By Ilana Koegelenberg
When it comes to designing HVAC systems for shopping malls, there are many factors to consider – what do the professionals say about the dos and don’ts?
Shopping malls are still going up left, right and centre in South Africa (despite a seemingly global move towards smaller, individual stores). Sometimes these malls seem to pop up overnight. There is more to these projects than just putting up walls, though. Most (if not all) of these developments boast carefully thought-out HVAC installations.
But why do we need HVAC systems in shopping malls and how should these be designed and maintained optimally? We chat to both engineers and contractors to get their insights.
“It’s not a case of ‘needing’ air conditioning in shopping malls, but rather ensuring the comfort and shopping quality for customers and patrons,” explains Graeme Page of Graeme Page Consulting Engineers (GPCE). “In today’s highly competitive retail market an air-conditioned environment both in the direct shopping areas, as well as malls and communal transition spaces, is essential to ensure comfortable surroundings and a quality shopping experience.”
Craig Blankers of WSP agrees. Two of the main focal points regarding shopping mall HVAC systems is compliance with South African National Standards (SANS), as well as human comfort levels of shoppers, he explains. “It is important to ensure shoppers are exposed to optimal comfort temperature settings as well as sufficient fresh air. The more comfortable a shopper is within the space, the higher the chances are that the shopper will spend more time browsing, potentially buying, and enhancing the experience by enjoying a good meal at a restaurant.”
But there are other reasons as well, explains Stefan Sander of Two Oceans Air Conditioning, a local HVAC contractor. These include:
- Ensuring that the servers of all tenants are kept at the correct temperature for correct function.
- Minimising disruption of the working environment of mall occupants and employees.
- Extraction systems get rid of indoor pollution such as spores, fungus and bacteria, reducing the likelihood of illnesses spreading.
- Kitchen extraction systems ensure adequate ventilation from cooking and prep areas around food vendors.
When it comes to designing HVAC solutions for shopping malls, what must be taken into consideration?
Blankers lists multiple factors:
- System efficiency – Electrical consumption versus how much cooling and heating the system can provide.
- Building application – What the intentional use of the building will be.
- Capital cost versus payback period – How much the client will end up paying for the air-conditioning system today and how long it will take them to recover these extra costs of a more efficient system from the resultant energy savings.
- System longevity – The serviceable life expectancy of the system before product quality and system performance deterioration.
- System flexibility – Will the system be able to cope with any alterations, variations and possible additions to the building’s initial application?
- Location – How far are the nearest sub-contractors located the site and what are their capabilities?
- Plant room space available – Are there space restrictions from the architect and is the HVAC plant to be constricted to a specific area?
“It is essential to obtain a clear and defined brief from the client as well as prepare a fully detailed design report which can be agreed with the client before the detailed design commences,” advises Page. “Different types of malls will dictate different types of design.”
Open ‘strip’ type malls without enclosed and weather-protected transition mall spaces will require a totally different solution to an enclosed mall with large demarcated food courts, large retail boxes, fashion and banking malls, transition spaces with roof lights and entertainment or showroom types of areas, says Page. “These mall transition spaces areas are treated very differently to the shop spaces and need to be carefully designed and engineered.”
It’s important to ensure that the HVAC system is correctly sized and designed to ensure comfort during all seasons with no uncertainties in the final design, adds Sander. You should also take co-ordination between other services into consideration and make sure there is enough space for the HVAC system. There are several factors that affect the space availability, including walls, ceilings, fire sprinklers, and ducting.
Make sure that all health and safety regulations are also met and that the aesthetics of the building in terms of feature design are taken into consideration, advises Sander.
Standards and regulations
Standards and regulations affecting shopping malls are similar to those encountered for any commercial type of building, including local council regulations as well as National Standards.
Blankers highlights a few:
- South African National Standards (SANS) 10400-XA for both environmental sustainability (Part X) and energy usage in buildings (Part XA). SANS 10400-XA refers to energy efficiency and energy use in the built environment. This regulation stipulates various design and operating parameters with which a building is to comply. For example, the maximum energy demand for various classifications of building applications is given in VA/m2 and kWh/m2 for various climatic regions depending on where the building is located. Therefore, it is imperative to design the most energy efficient HVAC solution, as well as ensure that the building itself contains the most effective insulation materials for wall and roof assemblies to ensure this objective is achieved.
- SANS 10400-O for lighting and ventilation regulations. SANS 10400-O refers to lighting and ventilation design and use in the built environment. This regulation covers elements such as interior lighting (both natural and artificial) as well as ventilation (both natural and artificial). The lighting will affect the HVAC heat load requirements and also determine the type of shading or blinds (if required) to be installed for optimal comfort levels and building performance. The ventilation portion of the national standard stipulates minimum outdoor air requirements in both air changes per hour and litres per second per person, as well as the minimum requirements for natural ventilation to suffice.
“It is also highly important to be cognisant of the internationally banned refrigerants which aren’t banned locally as yet,” says Blankers. “This is important for future-proofing the shopping mall’s design and ensuring its longevity.”
In addition, should there can be any particular standard related to special energy standards or “green” requirements such as a GreenStar rating, that would also need to be included into the design, explains Page.
Choosing the right system
So, which possible HVAC systems are available for retail projects and how do they compare?
The choice of an HVAC system depends on the considerations mentioned, and the client’s objectives.
For example, when designed correctly, natural ventilation via cross-flow systems as well as stack ventilations are highly effective, explains Blankers. Variable factors such as wind direction and speed, as well as sunlight for solar chimney arrangements must be considered.
Mechanical HVAC systems include variable refrigerant flow (VRF) systems, direct expansion (DX) split systems, chilled water (water and air cooled), evaporative cooling systems, various hybrid and even geothermal (combination of mechanical and natural cooling) systems.
“Each one of the above systems has its pros and cons. It is almost impossible to compare systems options without looking at a holistic view of the conditions of the project,” says Blankers. For example, evaporative cooling systems would be less efficient in high humidity areas and complex control configurations would be problematic in rural areas without the requisite maintenance back-up. “The type of mall is critical to your solution,” says Page.
Page shares some general tips: Open strip-type malls can easily be treated by means of direct expansion (DX) split hideaway units for the standard line shops, with medium to larger air cooled packaged plant for any of the mini-majors or major stores included in the centre.
These types of centres will typically have two or three major/mini-major tenants with one of the leading food market stores on one end of the mall and a clothing/food tenant or pharmacy related tenant on the other.
There is also generally a stand-alone or drive-through store that can be treated in the same way as the line shops. Should refrigeration piping runs prove to be excessive, a VRF system can be designed, but this will increase the budget for the centre as well as “complicating” the design around individual energy usage, potentially limiting changes and addition of shops later.
“For the larger enclosed mall type and regional shopping centres, systems used vary from chilled water air handling units and fan coil units to rooftop air-cooled packaged plant(s)”, says Page.
Larger regional centres have been designed very well using only a chilled water solution, where major stores and mini-major tenants have their own chilled water generators and air handling units, while the standard line shops have a shared chiller serving fan coil units, says Page. “Energy usage is catered for by including energy meters into the design of the fan coil units.”
He adds that so-called ‘smaller’ centres have also been really well designed using the chilled water solution above for the standard line shops with packaged plant(s) providing air conditioning to the majors and mini-major tenants. “GPCE have also used a shared packaged plant alternative for line shops very successfully over the years. This makes the first fix design very simple and does not rely on having tenant layouts at such an early stage of the project.”
Maintenance of HVAC systems varies from system to system, but regular maintenance is imperative.
When HVAC systems are designed, the designer will design the system to specified parameters to which the system will operate. There is always a tolerance built into these design parameters to overcome ‘foreseen’ obstacles to an extent.
For example, when an outside air ventilation system is designed to introduce air into a shopping centre, the static pressure of the ventilation fans will be designed to overcome a specific static pressure drop over the filters, explains Blankers. Should the filters not be cleaned, the fan will not operate to the required design capacity and the system will lose its efficiency. Therefore, the HVAC filters are to be regularly maintained and cleaned to ensure optimal performance.
The same can be said for cleanliness of cooling and heating coils, chilled water strainers, kitchen canopy extract ducting, etc. “All these components are integrated to desired operating conditions and once the design tolerance is breached, the system will not operate at the desired efficiency and the system will be less effective,” Blankers explains. Should the system be variably controlled, the fans will have to speed up to overcome the static pressure of the dirty filters, or insufficient outside air will be introduced into the building should the system be constant volume.
“As a result of the HVAC system consuming a large percentage of a shopping centre’s operating costs, it’s essential that factors leading to system inefficiencies like poor maintenance schedules are minimised,” says Blankers. Although putting together good maintenance schedules might seem like an easy task, it’s also essential that the system is designed to ensure that all mechanical components are easily accessible to be maintained. “Although this might sound like a given, we often see component failures and replacement thereof being extremely difficult as access is often an afterthought.”
Another point is making sure that you allow suitable and easy access to plant. “It is preferred that service takes place externally to the shop on roof plant areas, but this is not always possible,” says Page. Access to these roof plant areas needs to be via a regulation-approved cat ladder and suitable access walkways across sheeted roofs if necessary.
Where fan coil units and air handling units are located above ceilings in shopping areas, these need to be carefully designed with the tenant’s architect or designer to ensure large enough and suitable access, advises Page. It would be preferred if these access panels are situated in back-of-house or stockroom spaces to prevent step ladders and maintenance personnel from disturbing shopping clientele in the trading spaces. It’s also essential that the access panels are large enough not only for servicing of equipment, but also replacement of some parts such as fan motors, should this be unavoidable.
The design of the systems should reduce maintenance and service as much as possible as it’s common in older centres to ignore or delay servicing of the plant, says Page. “This will lead to early breakdowns, resulting in high capital costs to refurbish or replace systems well before the end of their planned life.”
The to-do list for maintenance is very thorough, from checking that filter clips are in place to checking the fan for proper rotation and even checking the insulation on the chillers. It’s important that you get a contractor who knows what they’re doing and doesn’t take any shortcuts.
It’s particularly important to keep all filters clean, says Sander. “Dirty filters or drip trays are a breeding ground for all sorts of nasty bugs if left uncleaned or not replaced regularly. Sick Building Syndrome is not a myth!” Dirty filters compound the sludge build-up in the condensate system, especially if falls are marginal.
Dirty filters result in reduced airflow, drastically reducing the capacity of the plant, and making it run out of its design conditions, putting strain on the refrigeration system. They also result in lower off-coil temperatures, which produce more condensation, and in extreme cases result in the freezing up of the indoor coil, he explains.
The outdoor units also need to be cleaned to ensure adequate or efficient heat transfer, otherwise the temperature or pressure can rise, putting the compressors under unnecessary additional strain, Sander explains. This leads to premature replacement of compressors, which is an expensive exercise, requiring degassing, re-gassing, etc.
“Maintenance is a relatively insignificant cost in a mall, and will ensure a cleaner, healthier working environment,” says Sander Also, maintenance is key to keep your equipment in good condition and to secure (and keep) your guarantee or warranty.
Design dos and don’ts
“In designing centres, it is essential to engage with the client at an early stage and agree on basic design principles and standards,” Page reiterates. If possible, obtain a tenant mix plan at an early stage. “We believe that spending a lot of time in the early stages of the preliminary and feasibility design, especially on plant area extent and positions, will ensure a smoother design later.”
It’s also essential to meet with the architects and internal designers early to discuss major elements such as open mall areas and roof lights. The type, size and detail of roof lights in the malls can influence the air-conditioning design in terms of heat load and air distribution and need to be carefully considered, says Page.
Another issue is that often tenants dispute the breakdown of costs pertaining to their HVAC bill, explains Blankers. “It’s a good idea to have these conversations upfront with your client to understand how the tenants will be billed and what will be stipulated in the tenants’ agreements, as well as what the client’s expectations are of the system.”
One option is for each store to have their own electrical distribution board (DB) which provides the store with the required power (electrical outlets, mechanical HVAC, etc.). Of course, this is dependent on the type of system designed and budgetary allowance, but this enables energy meters to be easily installed for each store and the exact electrical consumption can be calculated for that store alone. This will eliminate any disputes over different operating hours, shop applications, internal heat loads, etc.
It is also important to design systems with the local support capabilities in mind, says Blankers. “Do your homework to find out what capabilities the local installers and maintenance teams have, what their limitations are and where their expertise lies.” Designing complex, state-of-the-art HVAC systems in rural areas where extensive programming and troubleshooting are required might be impractical should the local maintenance teams not have the relevant training and experience.
Sander advises allowing for design flexibility for future occupancy or tenant changes. “Also, don’t take shortcuts or compromise the design in terms of the requirements of the regulations for things like fresh air and extract air volumes,” he says.
The HVAC system accounts for a large amount of the operational costs of a shopping mall. “Therefore, it is imperative to design with an energy efficient mentality,” Blankers advises. Electricity demand in South Africa is increasing exponentially and suppliers are struggling to keep up, so sustainable designs are vital.
Blankers shares a list of some simple and complex solutions to achieve energy savings in shopping malls:
- Implementation of natural ventilation where possible.
- Installing timers and/or occupancy sensors on the HVAC system to automatically shut down when the shopping mall is closed (or alter set points).
- Fresh air pre-cooling designs.
- Solar power incorporation with HVAC systems.
- Economy cycle on AHU’s for free cooling.
- CO2 monitoring to avoid treating and supplying unnecessary fresh air into the building.
- CO and NO2 monitoring systems for basement ventilation optimisation.
- Efficient canopy extraction hoods that require less extraction rates.
- Heat recovery via heat recovery wheels and wrap-around coils.
- Making use of systems heat rejection for free domestic hot water generation.
- Ice storage for off-peak consumption and reduced grid load during peak hours.
Also, Page suggests meeting early with centre tenants to establish lighting and equipment loads and discuss with them and the electrical engineer any methods to reduce energy loads and running costs of the air-conditioning system.
In situations where a packaged air-conditioning plant is “shared” among a few tenants, an early discussion is essential with the operator of the centre to clear up any confusion there may be later in establishing electrical running costs of the system and how the costs are shared, says Page.
Some tips from Sander include:
- Installing a building management system (BMS) that is programmed to switch the units on/off when the areas aren’t being used.
- Keeping units clear of debris and making sure regular maintenance is done (the cleaner the unit, the better energy sufficient it will be).
- Removing old, inefficient equipment and installing new equipment equipped with an inverter compressor.
“The harder your unit needs to work to get to your set point, the more energy it uses,” says Sander. Try and have your room temperature set point closer to the outside temperature (comfortable temperature). He explains that an energy-saving building can also be designed by taking climate into consideration and using the elements to design accordingly.