By Ilana Koegelenberg
As we continue our look at HVAC&R in application, we chat to industry professionals about the ins and outs of cold storage projects and how to offer clients the best possible solution for their needs.
After getting various comments over the years that we don’t emphasise the ‘R’ in RACA Journal enough, the 2019 features list includes a number of refrigeration features. For this edition, our refrigeration journey focuses on the topic of cold storage: very relevant considering the number of cold stores I see going up not only in Johannesburg, but around the country.
Just to make sure we’re on the same page, a cold store is a large, insulated refrigerated room or building designed for storage of goods in an environment below the outdoor temperature. Products needing refrigeration include fruit, vegetables, seafood, meat, and anything else perishable – even already frozen goods like ice cream.
These stores can be located on the farm itself or even at the point of shipping at the harbour, or at any link of the cold chain. Some are owned by the client directly, and many companies rent out cold storage space for smaller clients or those who don’t want the hassle of running a cold store themselves.
We chat to local contractors and engineers about how to design these systems as well as how to install and maintain them. What regulations govern these installations and how do you improve energy efficiency? From challenges to trends and everything in between — read more for your ‘crash course’ in cold storage projects.
You can’t simply build a cold store any which way you want. There are numerous regulations and standards that need to be followed, in particular, to obtain an Occupation Certificate for a building, which insurance companies are starting to demand on new build projects, explains Christo van der Merwe of Marine and Refrigeration Engineering (MRE).
Some of these regulations include:
- SANS 10400 (structural steelwork, building works, building efficiency, and fire engineering)
- SANS 10147, SANS 347 (refrigeration installations)
- SANS 10142 (electrical installations).
There are also various product-dependent regulations, explains Grant Ford of Matador Refrigeration. For example, pharmaceuticals and flammable products must adhere to strict health and safety regulations, including that electrical work must have a certain amount of protection to avoid sparks should a malfunction occur.
Temperature logging and control are also key to ensure the product doesn’t go off and as such, monitoring of temperature (especially for long term storage) is very important.
Also, shelving comes with its own regulations and weight and volume need to be taken into consideration so as not to affect air flows and maintain even temperature throughout the cooling space.
With so many different options when it comes to refrigeration solutions for cold stores, how does one choose the right system for your project? It will obviously depend on the type of product being stored, but there are other considerations.
Ford explains that the following are usually considered before selecting a system: energy savings, eco-friendly requirements, and user-friendliness. Then there are the usual requirements: insulation thickness, size, lighting, access (manual, forklifts or trolleys). Also, airflow is critical to achieve constant temperature throughout the room.
“The humidity required depends on product requirements. It’s crucial at all times to avoid having the product integrity compromised,” says Ford.
According to Ford, the considerations when choosing a system nowadays are linked to:
- Mechanical systems:
Simplex – single compressor application
Multiplex – multi compressor application
- Refrigerant: Hydrocarbons, ammonia, CO2, or synthetic refrigerants (HFCs mainly).
- A multi-rack also provides a more controlled temperature range.
One of the main considerations for selecting a system relates to the refrigerant used in the system. Locally, HFC refrigerants are still the most common solution (and generally the cheapest) but as the imminent global phase-down starts taking effect, many are looking at more natural alternatives such as hydrocarbons, ammonia, or CO2 systems.
Van der Merwe explains that the most common systems are as follows:
Industrial ammonia is the most appropriate system for large installations and has the best coefficient of performance (COP) available. These systems are designed for a 30-year plus life span and offer excellent reliability if maintained correctly. For the smaller sized cold store installations, the first costs can be considerably higher but over a 20-year life cycle costing, which takes into account the total operating cost, the ammonia option can be an attractive proposition.
CO2 cascade systems
CO2 is established as a preferred ‘green’ solution for supermarket applications and is being considered for certain low temperature applications such as freezer stores. CO2 (sub-critical) cannot match the COP of ammonia plants though. CO2 (trans-critical) COPs are just starting to match typical air-cooled R404 COPs and the higher ambients in South Africa must be taken into account when evaluating the total operating costs of this solution.
R404a, R507, and other HFC cocktails
Air-cooled synthetic refrigerant systems are a popular choice for small cold storage applications, typically up to 150 or 200 pallets of frozen storage. These systems have a lower first cost but the running costs are higher (due to a low COP and high electrical costs) and often the maintenance costs can be higher due to low quality installations with gas leaks and equipment failures.
It’s important to calculate the medium temperature (MT) load required compared to that of the low temperature (MT), in particularly a distribution centre (DC) application, advises La Grange. The COP of the LT load is significantly lower than MT applications, regardless of the refrigerant used. “That is an important ratio to consider when comparing one installation with another.”
Installation do’s and don’ts
So, you’ve selected your system – now it’s time for the installation. Before you get started, La Grange advises that you do the homework and review the potential payback period of each system and make sure you have facts and figures to back up your project planning. Get the recorded weather data (wet bulb and dry bulb) from the area where you intend to do the installation. “Verify your hypothesis with sound facts. Cross-check your work with existing operations if possible.”
Everyone recognises the importance of not looking simply at initial or CAPEX costs and also looking at what the expected payback period of the project is. A more costly installation might save significantly on running cost (energy consumed to operate). “The ratio of the installation cost vs. operating cost vs. maintenance cost is becoming more widely used to compare installations,” says La Grange.
Another crucial factor is to ensure your heat load calculations are correct, says La Grange. “Few things can save or waste more energy than heat load calculations that don’t consider all relevant factors.” Also, use well-established guidelines like the Total Equivalent Warming Impact (TEWI) to compare alternatives.
Size also matters – especially when it comes to the refrigeration plant. If you are too conservative and the plant ends up being oversized you might adversely affect the viability of the project, explains La Grange. A system that is oversized for the application might end up being less reliable when it is required to operate at part-load conditions in the winter. Too small and your customer’s room will struggle to reach operating set point during the warmer ambient periods.
Here are some additional tips from Van der Merwe:
- Budget for regular maintenance.
- Consider installing mobile racking to ensure that the size of the cold store is minimised for the pallet holding capacity with the subsequent reduced running costs associated with a smaller cold store.
- Be careful of going for the lowest cost solution without considering the possible differences in equipment capacities/ specifications and the effect on the running cost. The short-term benefit of a low first cost can be quickly overcome by high running costs and poor plant performance or production or product losses.
- Consider the contractor’s track record and the calibre of clients that he serves regularly.
Ford advises the following:
- Either you know how to do it or you don’t — don’t overcommit.
- Updated and correct qualifications are a must.
- Ensure that the correct design is done for the required plant output.
- No shortcuts.
- Make sure you account for more than enough capacity.
- Don’t compromise on insulation.
- Understand the mandate.
These are Smith’s tips:
- Make sure that piping and equipment are kept dry and clean when being stored prior to installation.
- Ensure that pipe insulation is glued and joined correctly.
- Ensure that free air movement is allowed for around all insulated piping.
- Ensure piping is installed for effective oil return to the refrigeration plant.
It’s never quite as easy as it looks. What are the possible challenges of working on a cold storage refrigeration project?
“Energy savings vs. price is a major challenge,” Ford says. People generally want the most efficient plant but have a very tight budget, so the more expensive units are cheaper to run and have a high return on investment. “The cheaper system may not offer long-term running and energy savings. Clients want a Rolls Royce for the price of a Citi Golf.”
Then of course, the time frame allocated for the completion of the project is a major consideration. La Grange explains that often good solutions aren’t considered because they can’t be installed within the tight project schedule.
The electrical supply available on the planned site is becoming more relevant too, according to La Grange. Expanding the electrical distribution network requires long-term planning in most cases. In some cases customers pay for transformer upgrades at huge cost before considering a more energy efficient system. “Good empirical evidence can help many a customer not make that mistake. Electrical upgrades are very costly,” he says, and can cause major delays.
Another challenge is designing a system that can match the part load conditions closely as well as the full load conditions required, says La Grange.
Ford says it can be tricky satisfying customer needs as well as incorporating their needs into a practical design. “Sometimes the customer wants one thing but the product being stored has other requirements.”
A big concern in our local market is that R22 (an HCFC) is still almost half the price of most HFCs in spite of the fact that it is a refrigerant with an ODP and illegal to use in new installations, says La Grange. One factor seems to be the very low purchase cost of R22 from the manufacturers in the east by refrigerant importers.
Looking at maintenance
A refrigeration system (usually) works 24 hours a day. If you drove a car at 100 km/hr for 24 hours a day, then you would cover ± 70 000km per month. This gives an indication of how hard a compressor works and the need to maintain it before it breaks down, Van der Merwe explains. “Planned maintenance is critical to ensure the plant operates reliably and at peak efficiency.”
If you consider the value of product that is being stored in a freezer store, the potential loss of product, and the implications of finding alternative storage costs at short notice, then it is a better bet to carry out the scheduled maintenance, Van der Merwe says. “Scheduled maintenance is generally a predictable cost with reliable operation at expected temperatures as opposed to running until the equipment fails and then scrambling to sort out the problems and potentially dumping spoiled product.”
According to Ford, it’s key that service contacts are put in place to maintain the system. “It is important to note that operation costs can increase due to unmaintained systems.”
“Maintenance is an ongoing process and aims to prolong plant life and reduce down-time resulting from breakdowns,” explains Merrick Smith of Pro Active Refrigeration. The maintenance programme should, amongst other duties, include leak checking, oil changes, filter changes, and condenser/evaporator cleaning, he advises. Mechanical and electrical checks must also be conducted so that worn parts can be replaced.
La Grange shares some maintenance essentials:
- Having qualified technicians with the required South African Qualification and Certification Committee for Gas (SAQCC Gas) licence.
- Having extensive commissioning information to refer to.
- Minimising leakage rates and doing regular refrigerant checks.
- Minimising downtime that would result in stock losses with planned maintenance.
- Keeping records.
Energy efficiency is a massive consideration for most HVAC&R projects and cold stores are no different. “Energy saving has become very important for all users of refrigeration of late,” says Smith. Energy saving does come at a cost and the more energy saving devices or systems added, the greater the CAPEX. “Energy saving comes from efficient design and the use of energy efficient alternatives when selecting your equipment.”
First cost is generally a once-off cost if the correct equipment is supplied and installed, explains Van der Merwe. “It is accepted that it costs more to install a system with a higher efficiency, but it is money well spent and it will pay for itself.” Running costs are incurred on a continuous basis for the entire life of the plant and this quickly outweighs any capital cost savings if you install a low-cost system with high running costs. Electrical costs will increase annually, so this cost portion will only get worse. “It is strongly recommended to spend more upfront in increasing the equipment specifications /capacities to reduce the running costs.”
“Energy savings are probably the most important factor right now, especially in South Africa with the price of power constantly increasing,” says Ford. “You can achieve efficiency simply by lowering your operating pressures using quality electronic control systems. Installing soft starters and variable speed drives on the compressors are also good ideas.”
A look at trends
Being environmentally friendly is one of the biggest trends currently, explains Ford. “Environmentally aware products, such as CO2 systems are slowly becoming more cost effective to use too.”
La Grange concurs, explaining that clients are putting large trans-critical installations in place of what might traditionally have been ammonia installations. He adds that globally, the use of hydrocarbons like R290 and R600a is also growing dramatically.
On the industrial side, a lot of R&D has gone into alternatives to modulate the capacity that screw compressors offer on the larger systems, says La Grange. Most compressor manufacturers have invested heavily into this.
“It is generally a stable industry and change is a gradual process,” says Van der Merwe. But he has noticed a move towards installing more electronics for plant monitoring, data logging, and off-site access to plant operational information. “The available solutions are becoming more affordable while offering similar levels of information and storage.”
In addition, the industry is becoming more cost conscious and this is putting pressure on quoting for a good technical solution with redundancy and providing some form of back-up for equipment failure vs. equipment selections that are marginal and possibly undersized, says Van der Merwe.
“It should be borne in mind that if an air-conditioning system fails to perform, then the people may complain that it is too warm but it will still be more comfortable than the outside ambient conditions,” says Van der Merwe. “If a cold store installation fails to perform as required then the client’s operational requirements may be compromised and product quality and shelf life could be negatively affected.”
Executive summary? If you’re going to build a cold store, do it right or it’s going to cost the client a lot of money in the long run.
The extended version of this feature with more technical detail will appear in the July/August edition of Cold Link Africa.