Andrew Heggie wrote:
wrote:

I'm not really following you there, but theres no need for any valve or
air hole on the pump side. The pump will be an impellor type, not a
piston, so the water drains back through it once stopped.

It's a bit like those bird drinkers where the reservoir of water is inverted
and the column of water only allows water into the drinker when the level
in the drinker drops and allows a bubble of air in. In this case we have a
loop of pipe and panel filled with water, the legs of the loop will not
drain as there is nothing to replace the water column, so you need a way of
bleeding air into the top of the loop to break the stagnant syphon.

The panel output leg has a 1/4" hole near the top of the tank. As soon
as water stops flowing, the water in the output leg is replaced by air
that enters this hole. At this piont you then have a panel full of
water, and one leg full of water, one empty. The lot empties back
through the pump. There is no need for any hole high up. The one must
is the panel output piping must be at least half inch, not quarter
inch, so that air can go up and water down at the same time.


This falls apart if the height difference of the solar circuit top to
bottom exceeds about 9m.

not many lofts that high

No but you may be tempted to house the pump and F&E tank on the ground floor
or basement with the panels at the top. As someone pointed out if pumping
power is high the electricity cost could negate the value of the solar
input.

There are no doubt many ways to cock a design up. It seems logical to
confine our examinations to competently designed setups.


£63 per panel? Use a few, space heat in winter, water in summer. Run
the numbers to see how many gets you best result.

Yes that's what I thought, maybe worth considering for a new build, pitched
roof with a few cms of celotex underneath, I'd have to review the nuances
of "warm" roofing again.

You wont get 75% efficiency for hot water, but can for hot air.

It looked like this was possible from the SAP pdf, what makes you think it
will be worse on water and better on air?

Air target temp is low, the output air need only be mildly warm, low
temp panel operation equals good efficiency. With hot water the target
temp is close to the stagnation temp of the panel, so once the water is
halfway hot the panel efficiency is way down. If the water ever reaches
panel stagnation temp, efficiency has by then dropped to zero. This is
one of the various plusses of hot air panels.

Curious how you plan to use the same panels for both water and air


NT