Well-insOlated is good...
Radiant floors with lots of house insUlation and airtightness
can work well with solar heat, since the water temp can be low.
You might enjoy collecting hot water in fin-tube in an air heater inside
a sunspace and heating the house with sunspace air on an average day...
And you might avoid certain kinds of evacuated tubes, eg
http://www.siliconsolar.com/shop/catalog/Evacuated-Tube-Solar-Collectors-p-16145.html
One opinion:
... you will find a lot of this type of tube collector... The question
you always need to ask these importers of off the shelf collectors is
for the approvals certifications, both SRCC and SPF as the very minimum.
... this sort of tube shows a central located standard low efficiency
heat pipe... The problem we found with these type of tubes... is they
will implode if they are left exposed to hot and very sunny weather for
a long period of time without the pump running or the closed loop circuit
always used in most of the world which ends up turning the water/glycol
to steam. The fault with that collector is the heat pipe has a flange
and a cup below the condenser itself which is then covered in a silicone
cap, which allows the heat pipe to be a very tight fit inside the tube
to stop the build up of heat escaping to achieve the heat transfer
through the heat pipe and into a copper heat exchanger which has 44
brazing points...
This collector being central located relies on the heated air in the bottle
to be transferred to the fins surrounding the heat pipe for it to work...
in 2 years of much testing, we had 4 homes in 2 weeks where the tubes
exploded, the reason was power cuts, and when the power came back on,
the thermal shock of cooler water hitting 350F in the heat exchanger
added to the problem. We also had 3 heat exchanger leaks...
All those companies who think when they order a vacuum tube collector,
they have all be approved and tested will get a shock, as 99% of all
sales in China are thermosyphon, as the cheapest installation option so
the chance of any of these overheating as a closed loop system is very low.
Just imagine these glass evacuated tubes 100% sealed up, outside in
blazing sun for hours on end with no heat being taken away through
the heat pipe which sits in a copper pipe inside a 32mm copper pipe
which has boiled the water and is at a temperature of 400F. It does not
take a lot of brain power to understand there is a limit of how much heat
pressure these tubes can take. Add to that, when the pump comes back on,
it's sending to the heat exchanger a temperature of 60F into a copper pipe
of 400 F, the thermal shock hitting that very hot pipe, sends shock waves
down the heat pipe as well. All of these imported collectors all need
a closed circuit system, to protect the heat pipe from freezing, those
that use this as a direct system are going outside potable water use,
as the welding of the copper with brazing rods are not approved for
potable water...
Nick
