Refrigeration Cases and Return Air

[Capt Steve]

Got a question for the group.
Many of the retail supermarkets pull return air for the HVAC from behind the open refrigerated cases. That helps to keep the back of cases dry, and keep the aisle warmer. Instead of pulling return air from behind the case, has anyone had any experience blowing tempered air behind the case and allowing it to mix with the case spillage in the aisle? If so, how did it work, or did it work at all?

[chillyhamster]

The mighty T used to install undercrofts, which carried all refrigeration pipework, electrics and drainage. The extract from the undercroft pulled air in through the kick strips. The main problem with this revolves around access. (working in confined spaces, access only with fan off with potential for heavier than air refrigerants to pool causing an asphyxiation hazard). T placed ownership of relevent BA equipment on contractor. High cost of building and operating, use of smaller scroll packaged plant on roof with pipe dropping down to cases removed this from all new sites. Cold isle syndrome depends on type and manifacture of cases together with effectiveness of H&V plant. In some instance where cold isle syndrome has occured then the fitting of small fans in the rear flue of multi deck dairy and meat cases taking warm air from ceiling level and blowing it out through louvered kick strips has solved this, But, can cause high ambient temp problems during summer months if shop floor is not comfort cooled or fans swithched off. Ok also for removing condensation from rear and underneath of full height frozen food cases (and well cases, but fans need to be fitted to the kick strips, But, the condensation is most probably caused by the progresive insulation failure which will lead to case replacement (fitting ventilation fans only delay replacement not prevent)

[750 Valve]

Capt Steve, have seen exactly what you are asking many times. Coles supermarket in Australia have used, and still do use both versions.
A common setup these days is a common shopfloor return air grille and ductwork splitting into two central AHU's, one serving the general shopfloor, heating usually via one HT rack heat reclaim (sometimes parallel, sometimes series with split condenser depending on heating requirements) and the other AHU serving to pump air down behind the cases and out through the kickplates, offsetting the cold aisle effect from the cases. Case mfgs developed ratings for max velocity at kickplate (cases now have 20mm gaps at top between kicker and case body) and max air temp, A/C is designed accordingly. Heat from this rack is usually from the MT rack and is usually in series with a split cond, if piped in parallel constant cycling can be a problem as cases can only cop 30'C air consistently behind them before any performance probs (according to mfgs) and with short cycling comes all the liquid level alarms as refrigerant doesn't have enough time to drain from the condender.
Generally this approach seems to work well, better than drawing return air from under the cases.