COLD STORES
to reduce the temperature to below freezing, hence turning the trapped moisture to ice particles. This early stage of frost heave will take time to develop, but the tiny ice particles combined with the grains of sub-soil create an increasing capillary network conveying moisture from the ground to produce an iceberg effect under the store. Ice, being of a greater volume than water and being trapped under the sub floor, exerts tremendous pressures, ultimately resulting in the cracking and lifting of the finished floor and creating substantial infrastructural damage. Several frost heave prevention solutions exist, some using fluid pumped around pipework embedded under the floor, some making use of waste heat from the condensers, some using wire elements at mains voltages while some use safer, low voltages to heat stainless steel wire elements sheathed with a tough PVC outer. Systems that use fluid benefit from being
relatively efficient while covering large areas, but the systems can be complex and costly. A failure anywhere in the plastic pipework can have catastrophic consequences once buried in the floor. Maintenance is also vital to the constant operation of the solution.
Reclaiming the heat generated by the condensers is an admirable solution, making the most efficient use of what would otherwise be wasted energy. However, the initial investment cost is high making this type of solution realistically viable only for large, industrial scale freezers. The use of mains voltage wiring has the benefit of operating at very low current and is easy to install but it is only really suited to smaller installations and there are obvious dangers associated with using mains voltages in situations where water may be present! Low Voltage wire heating is a safer option.
There are two methods of installation available, either using sheathed wire elements laid directly on the subfloor or laying the wire elements in pre- manufactured insulated boards. Both solutions are therefore fast and easy to install. Low voltage frost heave prevention solutions are suited to all sizes of freezer, from small to very large. Very long operating lives can be expected as the sheathed stainless-steel wires require no maintenance. Using thermostats to operate only when required, these solutions reduce waste and ensure optimal energy usage by maintaining the operating temperature (measured by under-floor probes) within designed parameters.
As it can be seen, there are benefits and
drawbacks with all the systems, so it is a case of choosing the right solution to match timescales and budget. Frost Heave Prevention systems are not only relevant to freezers. Often a chiller
is used alongside a freezer, operating at a higher temperature (often between 2°C and 4°C). Although this temperature is above the freezing point, there is still the opportunity for problems caused by water. The low temperature of the chiller allows condensation to form on any uninsulated part. This is often the floor! Occasionally, chillers are installed on upper floors of buildings. This is particularly common in specific regions of the world where high-rise buildings are prevalent. This has the potential to cause problems to the room below through condensation forming on the ceiling and dripping into the room. The level of condensation will depend on the temperature and humidity of the floor below. Condensation can create problems through damp, damage to goods, dangers from slippery surfaces as well as unsightly staining. To avoid condensation, the same measures used for Frost Heave Prevention can be applied. In essence, create a thermal barrier between the floor of the chiller and the structural floor beneath. To avoid risks from either frost damage or condensation, all exposed structural parts of a cold store need to maintain the thermal layer created by the frost heave prevention solution. Where floors of adjoining rooms are at the same level as the Cold Store floor, wall channel heating elements can be laid before the walls are constructed to ensure that a thermal barrier is created, preventing condensation and freezing creeping beyond the cold store. The same is true of stanchions and columns (whether concrete or steel) within the cold store, across thresholds of doorways (to prevent slips from ice forming due to condensation), and around doorframes which need heating to ensure that formation of condensation does not freeze the door shut.
Even temporary cold stores require FHP solutions. For example, while an existing cold store is being renovated it is vital for the food business to continue unhindered. In this case, temporary cold stores in the form of freezers or chillers can be erected on land that was not originally designed to house them. These temporary structures may well be in existence for extended periods, in which case it is just as important to prevent frost heave as it would be in a purpose-built facility. It is therefore important to ensure that all frost prevention measures for the cold store layout and type are considered before building commences. Even temporary cold stores require FHP solutions. Temporary structures, like inflatable freezer domes, are vital for a business to continue unhindered. Examples might be while an existing cold store is being renovated or to provide additional freezer capacity while a new freezer is being commissioned.
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Frost Heave damage making racking danger- ously unstable.
These structures may be situated on land that was not originally intended to house them and they could be present for extended periods of time. If this is the case, there is the potential for frost to cause damage or problems. Therefore, employing frost heave prevention methods to these structures is just as important as it is in a purpose-built facility so choosing a temporary structure that already integrates with FHP systems makes the most sense.
The selection of one solution over another depends on the size of area, the available budget, the availability of a maintenance budget for the lifetime of the cold store and the capability of the chosen supplier to manufacture and provide suitable products. Therefore, it is important for the project owner to share the architectural drawings of the site with the FHP provider(s). This partnership ensures that a custom-designed, bespoke heating pattern is drawn up, maximising the coverage of crucial areas, while ensuring exit points are identified for the control wiring. The longer a systems designer has to perfect this design, the better the end solution will be. Often there is little time at all, with FHP design,
production, and shipping (often international) being crammed into a few days before the floor concrete is poured! Obviously, this leaves little room for discussion, but it also places a great strain on the FHP manufacturer!
So, with all the detail that goes into designing cold store projects, why is Frost Heave and Condensation Prevention so often overlooked?
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www.thermatek.co.uk www.acr-news.com • July 2022 27
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