[Greenbuilding] Solar Water Heater architecture

[Keith Winston]

Hi David,

I'm also an Apricus dealer, in the DC area. Just to be clear, the reason 
Apricus collectors can stand stagnation is because the heat pipes can 
stand it: they are made using water as the working fluid, and are hence 
less prone to some problems heat pipes can develop. But there's a lot of 
interesting and complicated science rolled into any modern solar thermal 
collector.

One thing we haven't mentioned, when talking about the head/pressure 
involved with drainback systems, is that you only have to drain water 
back into the building envelop: you could have a system with 70 vertical 
feet of distance between the tank and collector, and yet only "drain 
back" 5 feet. In which case, the pump would only have to develop 5 feet 
of head, plus the resistance of all the pipes and fittings.

I hope that makes sense.

Keith


David Delaney wrote:
> 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
>
>
>
>
>
>
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-- 
Keith Winston
Earth Sun Energy Systems
3927 Madison St.
Hyattsville, MD 20781
301-980-6325
keith at earthsunenergy.com
www.EarthSunEnergy.com