A complete check prior to lowering the temperature of the cold room/ cold storage to the required operating temperature to ensure that the insulated room has been constructed in accordance with the specifications and the approved construction drawing. The following should be checked as appropriate;
- The integrity and continuity of the vapour seals is complete.
- The anti–frost heave heater mat, door threshold heaters and all trace heating are all operational.
- Pressure relief valves and associated trace heating are commissioned and operating.
- Lighting and emergency lighting including movement detectors are operational.
- The wearing slab has achieved the required strength measured by test cubes stored on the slab.
- The surface of the insulating sandwich panels and all other surfaces are clean.
- All elements of construction have received the required curing period as appropriate under the environmental conditions specified by the manufacturer (e.g. sealants).
- Fire detection systems, smoke and heat detectors, as appropriate, are commissioned and operational.
- Active fire protection measures are commissioned and are in active mode.
- All doors, both manual and automatic have been commissioned and are operational.
- Any omissions should be corrected and further time allowed for the floor to gain strength if necessary.
Temperature Reduction Program
The cooling program suggested by the Institute of Refrigeration is set out on the following table. The Institute of Refrigeration document states that the slow rate of cooling is to prevent the concrete floor cracking.
Recent research and actual successful practice has shown that it is possible to accelerate and more precisely define the time, at which the floor has reached the required in – situ strength prior to temperature pull down and to achieve a faster rate of pull down of temperature than suggested below.
The technique also has the benefit of reducing, if not totally eliminating, early age thermal shrinkage. Anti cracking fabric reinforcement and jointing of floor slab can also be moderated. The successful application of the technique, which can halve the time from casting the floor to achieving operating temperature, requires an overall understanding of all parameters affecting the thermal stressing, curing and gain of strength of the concrete slab. The specification of the materials and work program should be entrusted to an Engineer suitably qualified and experienced in applying the technique.
** 14 days is a minimum and may have to be extended indefinitely in order to achieve the required in – situ strength of the concrete under external ambient temperatures as determined from test cubes stored on the surface of the slab.
It is clear that the predictable concrete curing time and the reduced cooling program period noted above may have considerable cost advantages at a period when the construction of a cold store is frequently at its most critical.
Water Vapour Removal
Under ambient conditions at the time of installation the core material of all insulant panels naturally contains water vapour. When the cold store is lowered to operating temperature the water vapour is drawn to the cold face of the joints and this may result in an initial light frosting at the joint position. When the initial drying process is complete the foregoing light frosting will not recur. Checking authorities should note that the light frosting described above does not therefore necessarily indicate a failure of the external vapour seal.