Would 70 tubes be too many???

[stevie_f_2004]

I currently have 30 tubes (58mm) on the roof and looking to upgrade to 70 nr this year. Concern that I have, will 70 just be too much. I have a 300litre tank and average temperatures top to bottom during sunny days last year was 40deg. The family are pretty hard on water usage therfore is this about right??

Rgds

Stephen

[Brandon]

I would argue that 70 is over the top, by rights 40 ought to be about right, if doing it yourself I would try 50 first.

We put 90 onto a 300l heat store that dumps to a small pool, and the store heats very quickly when the sun comes out.  Until the pool was plumbed we dumped to 2# 210l water butts, and they got to 58^o in the first day.

[stevie_f_2004]

What I am thinking is putting a TMV on the outlet of teh storage cylinder therefore reducing the volume of hotwater required. This would give the benefit of the overcapacity of the tubes raising the water temperature yet giving protection of the 65Deg temperatures and "smoothing" peaks and troughs of sunshine/cloud cover...

 

[Baz]

The problem is the tank will boil on sunny summer days.

[KLD]

The problem is the tank will boil on sunny summer days.

A heat dump is an obvious MUST HAVE on such an over-spec'ed system.
If access to the roof (?) is easy, I'd side with Brandon and go for 50 tubes first and see. Upgrade to more if you really need to.  50 tubes translate to 4L/per 47mm equivalent tube, which should be plenty under "normal" conditions (south facing installation etc.)
OTOH, if access requires a scaffold and / or hiring external people, it's likely that a stepwise approach becomes uneconomical, in which case I'd take 70tubes and make sure the heat dump can handle the extra capacity.

Klaus

[stevie_f_2004]

Access is fine it is the postage costs that are the problem £100+ each time .....What I might do is install the 2 extra manfolds i.e. 2x20 and install 10 in each and see how it performs and add inteh tubes if necessary but at least the facility is there to be added /subtracted......

[dhaslam]

I would say that that the number is about right.    There are probably about thirty days in the year that you will have  a big surplus  but  for the rest of the year the extra  capacity will be useful.