[Greenbuilding] Solar Water Heater architecture

[David Delaney]

Under certain conditions, ordinary water makes a good 
working fluid for solar water heaters, in a drainback 
configuration. The evacuated tube solar water heaters made 
by Apricus claim to extend these conditions. Apricus is an 
Australian company. The tubes are marketed in North America.

http://www.apricus.com

The distinctive feature of Apricus tubes is that they are 
claimed to tolerate indefinite exposure to the hot sun while 
not containing water - "stagnation". This feature allows a 
collector to be configured in a drainback configuration for 
cold winters with short sun hours, then be run on a 
short duty cycle in the summer without damage when heat is 
not being removed from it by the working fluid, which is 
absent when no further heat is needed for domestic hot water.

One disadvantage of the drainback configuration is that it requires
greater pumping power, since each time the collector has to be
filled, the working fluid has to be pumped up to the collector
with the full weight of the column of water being pushed up the
up pipe by the pump. That weight is not balanced by fluid in the 
down pipe, since the down pipe is empty until the collector has been filled.

A dealer near Ottawa in Ontario: http://www.terravis.com

David Delaney, Ottawa