Calculating building system shutdowns in PHPP

19 September 2022 by Jason Quinn

It’s common for some non-residential buildings to be unoccupied for periods of time, during which the ventilation and conditioning is turned off. Schools and office buildings are common examples; think of after school hours each day or weekends where heating/cooling may be on only for 6 hours each day. In such circumstances, turning off ventilation and conditioning during the unoccupied period and then flush ventilating and heating up prior to occupancy can save energy, even in a building with a Passive House quality building envelope. As a side-note, most of the energy savings come from not running fans.

Here’s how you calculate this in PHPP. To account for the average lower internal temperature, adjust the average internal temperature using the chart in the PHPP manual. As you can see in the chart below, the temperature decrease is small because it’s also taking into account the warm-up energy. 

In the example cases explored by PHI, the same temperature correction factor was suitable for both heavyweight and lightweight building constructions ie typical European-style buildings and typical New Zealand-style buildings respectively.


Note Edited 17Oct2022 to correct the reference to shutdown over school holidays. This table is for reduced operation time over a day or weekend not for shutdowns for holiday periods etc. If you turn off conditioning over the school holidays you can have mould and other issues and we’d suggest a wider temperature band but keeping the equipment running for a period each day to maintain the indoor environment with as little energy use as possible. Thanks to those who pointed out the editorial error. I missed it. JEQ.

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