By Benjamin Brits
Although by no means a new technology, ice thermal storage can play a significant role in managing the biggest utility costs in any building – energy consumption.
On a global scale, one of the most significant trials to navigate is the supply of energy. What form of energy-mix is then next on the agenda – with renewables a first choice of course, then followed by how much energy is going to be demanded in future. This significant factor in the forward planning of the world has most country’s leaders at a stretch, relying on amongst other methods, computer modelling for various predictions.
Some experts would also venture as far as speculating that in terms of energy supply solutions and options, there is not much more that science can provide currently on the scales needed. Naturally, there will always be research and development into new energy generation methods, but feasibility and sustainability are always key, as well as optimising utilisation of available resources.
In the case of South Africa, the latter has become a limiting factor in our economic expansion with our energy supply not keeping to par with demand, and although we too operate on the international principles of peak demand tariffs, we also have the ever-looming factor to consider called load shedding, or load rotation, as it is commonly referred to now. This is also usually implemented during peak demand and directly linked to our generation capacity shortfalls.
An example of an in-tank coil unit for ice storage – this being a large application. Photo by Evapco
This particular outcome and the consequence that large infrastructure projects in the energy space continually face challenges, be they conventional fossil fuel operations or in ongoing movements into settling agreements in terms of renewable options, opens up a whole new world of engineering opportunities in this country – not to mention the fact that our existing energy infrastructure is ageing and is seen as another major risk to keep in mind.
Although an optimistic view is always held by the country’s leaders, energy experts and management from our own state-owned entity themselves have forewarned that energy supply will be under pressure for many years into the future.
South Africa’s challenges are not quite what the rest of the world experiences although the principles of energy supply sources, efficiency and global warming impacts are high on the agenda everywhere. Continual research is being conducted in how to manage thermal loads of buildings through alternative materials, building designs, techniques, and passive cooling methodology.
An image showing the ice built around the coils inside a tank. Photo by Evapco
You may be wondering as you read this why I’m stressing the energy factor in an ice storage feature, and for this, the simple answer is because no matter if you are looking at a new building, a retrofit, or a refurbishment, the fact remains that according to various global studies, commercial and industrial operations require the greatest proportion of energy a country produces (in some countries this is up to 80% of overall production), and of this, up to half of that demand can be allocated to HVACR needs.
In a commercial building setting or a production facility, the HVACR systems have always been designed and set up to manage the ‘worst case scenario’ or peak heating and cooling demand – this is the maximum output the system would need to provide when, for example, an office is fully occupied with all of the electronics in operation and at the hottest time of the day.
However peak demand is almost never a lengthy continuous occurrence. This then generally means that systems are designed to manage that demand for only a few hours a day – if even that long. However, during peak demand periods, stress mounts on the electricity supply grid and service providers as everyone needs energy at the same time, and also peak periods carry a premium in terms of costs per kW/hr to customers.
“The demand charge model is commonly found throughout the world and is essentially a mechanism for service providers to also manage their energy production capabilities. By charging more during these peak demand periods the idea is simply to try and balance the energy grid and incentivise users to either be more efficient, or transfer their peak demands to other times of the day. In some countries, off peak energy rates are five times cheaper than peak demand rates,” says Chris Elston – Calmac thermal storage engineer at KMS Engineering.
In South Africa, the consumer of the energy, no matter in what application, is charged a rate according to their peak demand. This is the highest averaged demand measured in kVA during any 30-minute period and within a designated billing cycle. This peak demand charge is an additional charge to consumption and supply costs.
This is how the ice pieces inside the tank look as they are melting down or ‘burning’. Photo by Evapco
So, for example if energy demand for nine hours of a ten-hour day (non-peak times) is 1kW (1.25kVA), but for the other hour the AC systems are on and now the demand increases to 7kW (8.75kVA), the peak demand charge will be based on the higher value – which is significantly more than 1kW for 90% of the time.
This scenario has created a multitude of innovations over the years because in all reality, efficiency can only take engineered systems so far, and because energy tariffs continue to rise while global warming persists, energy security continues to be a particular challenge here. Adaption and enhancement of existing technology is being sought out now more than ever.
Enter the humble ice storage solution
Commercially, ice storage for thermal applications was mainstreamed in the 1930s, but much further back in history, documentation has been found that Greek king Alexander the Great used ice for cooling applications around 300BC while other historians reveal widespread use by the Romans in the 3rd century AD – albeit that this technology was reserved and limited to only the elite and wealthy.
In similar research, Chinese and Japanese artefacts reveal that the eastern world had already advanced by storing ice (in what was known as ice houses or ice pits that were fully or partly sunken in heavily shaded areas) as far back as 1100BC.
“Today, ice thermal storage technology is advanced and comes in a variety of systems and sizes. Many of which have undergone decades of development. The system we specialise in for example, an ice ball system, has reached its third generation of design in order to perfect some of the challenges experienced over the years with earlier versions. The ice ball system was developed by French inventor Jean Patry over about a 30-year period,” notes Christo Vermeulen, director and Cryogel specialist at Intramech.
The prime purpose of ice thermal storage is to use energy at night, or outside of peak periods, to build up a predetermined bank of ice large enough to partially, or fully supplement cooling needs in a variety of applications.
“Inclusion of ice storage in a system enables a reduction in all of the components, foremost a saving on the cost of the equipment itself.”
These include both air conditioning and refrigeration applications, and as examples include:
- Air-conditioning applications
- o Hospitals
- o Shopping malls
- o Office buildings
- o Data centres
- o Educational institutions
- o Airports
- o Sports & Entertainment facilities
- o Hotels
- o Public Buildings
- o Mining
- o District cooling
- Industrial refrigeration applications
- o Food processing industries
- o Pharmaceutical industries
- o Abattoirs
- o Refrigerated warehouses and distribution centres
- o Bottling plants
- o The dairy industry
- o Power plants
- o Breweries
- o Entertainment venues
Here district cooling ice tank is being completed. Photo by Evapco
“Data centres being actively developed around the world have been using ice thermal storage for years, but more recently this application of the technology has been gaining popularity in South Africa as a sustainable and energy efficient solution for this market. This will be an important step to reduce peak power demand which is currently more critical in our country than overall consumption”, says Garid Glenn, Head of Marketing at Baltimore Aircoil Company.
The technology in ice storage has grown immensely over the last few years and today even the ice building process can be managed to maximise output through simple techniques such as flow control in refrigerant and heat transfer water circuits.–
How ice storage benefits a building or process requiring cooling
The main objective in using ice thermal storage as you have no doubt worked out by now is to shift cooling needs in part, or in full by banking energy, through either of a number of solutions, at a cheaper rate and to reduce peak demand charges and grid pressure. It is likened to the same principle as charging a battery for use as required at a later stage.
Many HVACR designs today, in the drive towards efficiency and ‘greening’ solutions take into account entire lifetime sustainability factors which include capital expenditure, operational costs and environmental impact (or carbon footprint).
A common yardstick for the client is the payback period of their investment. This factor is really ‘as long as a piece of string’ to work with, as the well-known saying goes, but for the purpose of illustrating the value associated to ice storage, a typical installation without ice storage that would have a payback period of 8 years (which can be perceived as long) can be modified to reduce the payback period to as little as three years by including ice storage – which now becomes very appealing.
“Ice storage is an excellent and very relevant technology system and will be more so in future, not only because of the obvious ability to save energy (and money) but also because it can be applied very flexibly in a large range of applications. It has also been proven that through the correct design processes, there is an opportunity to gain the lowest first cost chilled system versus a standard chilled water system”, says Andre van der Merwe, managing director at Evapco South Africa.
Ice storage comes in a variety of sizes and can suit a number of applications. Photo by Evapco
Inclusion of ice storage in a system further enables a reduction in all of the component sizing. Reducing sizes does not only save on the cost of the equipment itself that can be proportionally reduced, there are often savings on the installation cost too. Further to this, there are direct impacts on connected or related components. These include things like the electrical distribution, wiring, starters, transformers, and so on. These are beneficial impacts on both electrical and mechanical savings that can be transferred to the client.
In the past, thermal storage for cooling was achieved by using large tanks of cold water, but with the shift to ice, further benefits are possible such as greatly reduced footprints (ice systems require about one tenth of the volume required with water), more suitable temperature differentials, and an extended period of cooling supply (dependent on setup of course).
Effectively, with the inclusion of ice storage and creative design, you can supply chilled water to a building or process (for a limited time) merely with a couple of pumps which makes the solution highly appealing as well as competitive in our drive to reduce costs and energy demand.
System and sizing considerations
Ice storage, as mentioned, can be included through a number of techniques and systems that are available in South Africa, and in part or in full support of an existing system. It can be retrofitted to an existing system too.
“As the largest contractor installing ice thermal storage in South Africa, we have done some very big projects, for example, tanks with a diameter of 3.5 meter and length of 13 meters and also the small installations. We have, over the past 12 years, had the opportunity to see what systems perform the best. The designs come in all shapes and sizes and as already mentioned, this solution is flexible. An important factor to note with this solution is that at night ambient conditions are generally much cooler and so the process of building your ice, besides costing even less as you are using that energy out of peak times, it’s a lot more efficient than trying to build ice at a 35°C daytime temperature,” says Jan Wibbelink, managing director of HVAC Installations.
Placement of the thermal storage tanks that vary in size from a few cubes to massive tank structures the size of a sports field, can be below ground, in basements or plant rooms; on the roof depending on size and weight considerations, or even within a building’s structure where spaces are available. These can include shafts above or below lifts, stairwells, as well as service duct areas.
The ‘tanks’ required for building ice can be made out of a variety of materials, including plastic, steel and concrete. The main challenge to contend with is the fact that the storage tanks are heavy. One ton per cubic metre, so the bigger the tanks the more consideration needs to be given to weight parameters. This too could limit installation within or on top of a structure. Larger installations mean weight into hundreds of tons.
Positioning is also important to consider because of the chilled water piping that is required to be installed. Some clients may also not want tanks on the roof because of aesthetics or the space is used for other purposes, like entertainment, while other clients may not want storage in the basements because they may rent out the parking space.
When sizing the system, the two main considerations are addressing the building’s heat load, and secondly how long it takes to build up the ice in the tanks. Should only a short time be available, the task would usually be possible, however the equipment setup required would be extensive and may make this solution unsuitable. The longer the period is to build ice storage, the smaller the refrigeration system needs to be.
Here an internal tank view of the ice ball system. This method freezes the balls rather than around the coils and a glycol solution is circulated through the tank. Photo by Intramech
It is recommended in determining system sizing to gather data from a minimum seven-day, 24-hour exercise to establish lowest profile and peak demand. This also indicates specific activity based on the building or facility. For example, certain retailers have very little activity throughout the week but on weekends have a continual load to manage. Similarly, an office building may only need to cater to full occupancy on Mondays and Fridays as during the rest of the week employees are working from home.
As a simple example, taking a peak heat load at 1 000 kW of cooling required, there is a general guideline of 60/40 where a 600 kW chiller, that can handle the ‘normal load’ is installed. When the chiller runs out of capacity, normal load is being exceeded so it is then supplemented by starting the chiller with a 400kW ice storage system. The chiller then rebuilds the ice overnight and repeats the process during successive off-peak periods.
Various sensors are also available to monitor such things as the thickness of the ice, the variance in the tanks, the proportion of ice to liquid and so on.
“When sizing the system your two main considerations are addressing the buildings heat load, and secondly how long you have to build the ice in the tanks.”
Way forward and incentives
Many role players agree that thermal storage is a good fit within green building design and implementation. South Africa has a praised Green Building Council, that is very technically sound and up-to-date with all the latest trends and designs, however there are no incentives anymore in this country to push green technology, other than the desire to partake in reducing carbon emissions, and thus global warming. Therefore, it has been noted that only large corporations partake in green initiatives.
The ice thermal storage system of the Capitec head office in Stellenbosch has one of the country’s largest installations. Photo by Terry February
“The world’s problems can obviously be solved by human ingenuity; we have it within us. We have the skill and the technology, and we know what the problems are with regards to polluting the planet and global warming. However, you can have this ingenuity in infinite volumes, but if there is no clear desire to reduce your carbon footprint, or an incentive to change, things will always be an uphill battle. Many countries around the world incentivise property owners and developers to implement green technologies and particularly for a country like ours where incentives are required, this will remain a key factor in driving this solution to ultimately support our ongoing energy dilemma,” concludes van der Merwe.
|For further reading about ice thermal storage, please visit the RACA Journal website, where more information about how the various systems work, as well as technical information.|