The energy performance of buildings with considerable annual heat load is dependent on the ventilation air change rates (ACH). Buildings utilized for commercial use often have high ACH and therefore high annual heat load. In order for these buildings to have a reasonable energy performance a heat recovery system is often used to recover heat from the extraction air to the makeup air. There are different variations of these systems; one that is frequently used in Sweden is a run around coil heat recovery system.

The present paper summarizes the findings from the previous studies, and presents a comparative study, for three different cases; the traditional run-around coil heat recovery system; with a three stage on/off controlled heat pump retrofitted into the system; and with a variable capacity heat pump retrofitted into the system.

Annual modeling shows that by retrofitting a well-designed 3 stage heat pump to the system the annual heat recovery rate for the Stockholm Case can be increased from 47 % to 65 %. For the retrofitted variable capacity heat pump the numbers for the Stockholm Case is an improvement of annual heat recovery from 47 % to 66 %.

The modeling also shows that a well designed variable heat pump can cover 81 % of the ventilation heating demand and a well designed multi stage heat pump 77 % of the demand.