General Topics

Topic: Some thoughts on the active/ passive label in solar systems

From: page-ed

For those who attended the 96 ASES Mtg in Asheville, you might have noticed that the "passive" conference presentations included systems with at least some air handling fans. The reason is that good passive systems may produce heat excess during time periods or in spatial locations. If an entire living space is exposed to direct gain it may be unbearable at some times. Even temporary shading devices represent an active intervention. In some of these cases it is just as simple to move heat from an accumulated area to a remote part of a house where there is no direct gain.

Almost every system and particularly multi story systems accumulate heat where it rises and only an active sytem (fans) can bring hot air down. Few homes are so stable that there is not a location that calls out for a ceiling fan... by the same argument some designers take the view that every multi-floor house (including well insulated ones) should have a delamination system... simply a large chase and fan to pull air from the top of the house to the bottom.

The concept of a totally passive system in living space heating is possibly an extreme design goal unless it is mandated by a need to go off the grid entirely.Another consideration is that an active system may be entirely passive in accessing its storage... the active phase brings storage to a prime location (such as a radiant floor slab) and the passive release is improved because of the focus provided by the active system.. Direct gain through windows is at least a passive system , but limited to where a beam of sunshine can be deposited.
There are other important "value" sytems to consider besides the "active/passive" issue... another equally important measure of systems is not whether active or passive... but whether major and expensive components of the system are acquired freely... by use of existing pieces of the building structure. Don't just ask "is the system active or passive"? Ask..is the system integrated into the structure both in raw material and in effort of construction?