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Fridge load is key to natural ventilation for retailers

Thousands of commercial offices and public buildings across the UK have adopted natural ventilation for its energy saving benefits. But up-take in the retail sector has been much slower.

Energy is one of the largest operating costs for most retailers, so it is clearly in a business’s interest to be as efficient as possible.

What many retailers do not realise is that by carefully controlling the natural ventilation strategy of a building they can significantly reduce the refrigeration load. This is simply because fridges have to work less hard in lower temperatures and humidity.

Supermarkets are designed so that store conditions are maintained within a set of temperature and relative humidity conditions to optimise the performance of the refrigeration units.

While these buildings can benefit from reduced fan power as a result of using natural ventilation, the real prize of natural ventilation lies in the potential for a reduction in refrigeration load.

Examination of interior and exterior temperature and relative humidity data in a number of supermarkets has shown that if the stores could vary the amount of fresh air brought in, the energy savings could be enormous.

Up to 10 per cent of the store’s total energy load could be saved, which is especially useful when the increased supply of fresh air is provided for free by natural ventilation.

The ability of natural ventilation to deliver these savings, however, depends on understanding the energy of the building system. Many natural ventilation strategies are designed to simply minimise fan power, and the strategy needs to look beyond this.

First, it is important that using natural ventilation does not lead to less favourable conditions for the refrigeration units.

Second, the strategy should be developed to help the refrigeration units. This involves using natural ventilation to create conditions in the store that are as cool and dry as possible.

This is achieved by comparing the target interior conditions with the temperature and humidity of outside air and using the control system to decide whether the store would benefit from more or less fresh air.

The final, critical detail in forming a natural ventilation strategy is that part of a retail environment will involve mechanical ventilation, at least for the foreseeable future.

Toilets, bakeries, rotisserie and café areas will all involve mechanical extraction, and in some cases some element of mechanical supply too. Therefore, the design of the store’s natural ventilation system needs to factor in the impact of the mechanical ventilation.

In most instances and with an expert approach, there are often big savings to be made employing natural ventilation.

Over the past few years the retail sector has finally started to appreciate this, with a number of retailers now electing to adopt the technology as part of the overall building ventilation solution.

Dr Shaun Fitzgerald is managing director of Breathing Buildings