For instance, ground source
heat pumps tend to have higher efficiencies than air source units during the
heating season due to the relative stability of ground temperatures below certain depths, though air source units — which involve much
lower capital costs — have closed the gap in recent years as manufacturers have refined their design, and there is evidence to indicate that
space heating demand in many Irish buildings may be peaking in Ireland's frequently relatively mild but windy weather, as the guide to air source
heat pumps in Issue 24 of Passive House Plus discussed.