Industrial HVAC
September 1st 2008

Trying to maintain comfortable conditions in the workplace can account for a surprisingly high proportion of a factory's energy costs (estimates for the UK engineering sector, for example put it about a third) and there is a lot that can go wrong and waste energy. In this brief article Vilnis Vesma provides a few general pointers

If you have local extract ventilation systems, might they be able to run when not required? Are they in fact doing so? If so the solution might be training and motivation, or the introduction of timers or on-demand automatic controls. Remember also to check that existing timers have not been overridden or mis-set. Where the ventilation is needed to remove particulates (from grinding wheels or welding, for instance) it will generally be more economical to use a filter unit that returns the clean air to the space rather than exhausting it to atmosphere.

In a main ducted air supply system, dampers controlling air-flow should be checked for correct operation and appropriate control. This could be particularly significant where recirculation is provided: check that the control system is minimizing fresh-air makeup during the heating season. Blocked filters and grilles will reduce the effectiveness of a heating or cooling system and you may find additional heaters or air-conditioning being introduced that are not strictly necessary.

Where air flow is controlled by dampers, there may be scope for using variablespeed drives on the air fans instead. A 20% speed reduction halves the power requirement and very noticeably reduces the noise as well.

Areas such as loading bays and workshops which have high air-change rates are not best heated by warm air systems, and if they need to be replaced, consider gas-fired radiant heaters instead.

Remember, however, that radiant heaters need to be controlled by black-bulb thermostats because they provide comfort without heating the air. If you have independent warm air heaters (whether direct-fired or fed from a boiler system) with integral electromechanical thermostats, it may pay to upgrade to electronic thermostats fixed externally in the heated space. They provide more stable and accurate temperature control, avoiding wasteful upswings in temperature.

If your heating is supplied by boiler system there will be many risk factors. If you have two or more boilers ganged together, check that the boiler sequence control is working effectively, matching the number of active boilers to the load on the heating system. As long as the idle boilers are thermally isolated (by automatic valves or flue dampers) this will reduce standing heat losses. In office areas where heating is provided by radiators whose circuit temperature is weather-compensated, check that the water temperature modulates down correctly as the outside air temperature rises. Incorrect compensator settings or a faulty mixing valve could result in costly overheating in mild weather, especially where there are long runs of exposed heating pipework.

Not just in boilers but in all fired heating appliances, pay attention to combustion efficiency. Ensure that the fuel-air ratio of each burner is optimised and that exhaust temperatures are as low as is safely possible. These precautions will minimize the heat lost up the chimney: it is a universal opportunity that everyone can benefit from. If stack exit temperatures stubbornly remain high despite boiler internals being clean, try derating or downsizing the burner to make it a better match for the boiler it is fitted to.

Air conditioning is becoming ever more prevalent, and where it is already fitted, good maintenance will pay dividends. For example make sure that the condenser coil (which dumps the extracted heat) is clean and unobstructed. It should also have access to a free flow of air at the lowest temperature possible, and not (for example) be crowded into a confined space with other heat sources.

Where air-conditioning is not yet fitted but is being demanded, the recommended strategy is first to remove or reduce heat sources (equipment, lights, heaters, or sunshine). Next look at partitioning to segregate people from heat sources and to reduce the air volume that needs cooling.

Thirdly, establish the parameters: what are reasonable temperature thresholds for personal comfort and equipment reliability? Finally, having minimised the demand, review the situation to see if ambient cooling might be sufficient. Can you duct fresh air to a server room, or use overnight ventilation for precooling an office? I would emphasise the importance of effective time and temperature control -- a topic I shall return to in more depth in a later issue – and conclude with a recommendation to gauge weekly or monthly HVAC energy consumption against the weather, using degree-day measurements, so as to detect the onset of energy-wasting faults.

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