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  • Richard Weaver

The Parable of the Blower

A short story of how an efficient heating system was blown away.


This is an account from an ESOS survey of a retail company’s Head Office. This was a very smart new Head Office, recently completed and occupied with modern and efficient heating and air-conditioning equipment. The Head Office had a very nice training room, but the room was unusable because it was always too cold.


The manager was very upset about this. Along with her colleagues, she couldn’t work out how a new system in a new and well-insulated building couldn’t make them warm. They could switch it on, put the settings way up and hear it working, but no effective heating.


When I had solved it, I brought her back into the room, and the look on her face said it all:

“It’s warm in here! How did you do that?”.

The problem was not in any of the hardware. As nearly always the case, it was a fault in the settings of the equipment.


The HVAC for the room consisted of three split unit air-con systems concealed and ducted into the room through decorative perforated tubes. ( In the parlance, a ‘three-unit DX fan-coil system’ ) A small AHU was connected to the inlet of these fan-coils so that only AHU air passed through them.


The problem arose because the AHU was set at max output, and simply blew any heating effect from the fan-coils straight out of the building. The ‘solution’ above, was to turn off the AHU and let the fan-coils do their work.


It appears that the AHU output was never adjusted once it had been installed and tested. And because the ducting to the fan-coils was closed, all its output went through the units. Tested at full power, the airflow rate was many times the rate generated by the fan of the fan-coil, and so the heating effect of the unit was swamped.


The formal recommendation in the ESOS report was to “re-commission the equipment serving the training room”. I would also have encouraged the de-coupling of the AHU output from the fan-coil input, so that fresh-air ventilation can be controlled separately.


A recurrent theme in building energy efficiency is that it’s nearly always the settings that are at fault. Manufacturers, installers and maintainers ensure that their equipment works, but not usually how it works, and in connection with other systems.


Therefore, the lesson of this parable is ‘When you have a HVAC problem, look at the equipment settings first’.








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