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rcflyers

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Posts: 4
Reply with quote  #1 
I would like to fit a solar hot water system on my roof above an existing Velux window as this means I can easily fit it and maintain it myself.
My existing hot water tank cylinder an indirect coild in it which is heated by my system boiler.
The cylinder is in the airing cupboard on a stand and the top of the cylinder is 1.6 metres from first floor level.
I can remove the existing immersion heater from the top of the cylinder (never used it) and fit a coil in it's place that will have the hot solar water circulating through it.
However, to get the pipes from the proposed panel site to the cylinder means running them under the floorboards and it is a run of approximately 7 metres horizontally.
I can mount the bottom of the solar panel about 1.8 metres above first floor level.
I was hoping to put a tank and pump in the airing cupboard on the floor.
My question is:
Do you think that the water would drain back when the pump stops bearing in mind the minimal head between the bottom of the panel and the coil in the cylinder and the 7 metres or so of pipe run to connect the 2 together?
Thanks for any replies.

Old McDonald

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Posts: 66
Reply with quote  #2 
rcflyers, You do not say where you live, but from your post, and your use of English, I am guessing somewhere in the UK - ot at least you are of UK origin. 

I regret I am not qualified to answer your post, and I am rather surprised nobody else has come forward yet. Do not worry, they will because this is the most friendly forum you will ever find, and the knowledge and willingness to experiment is far beyond anywhere else I have seen. 
rcflyers

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Posts: 4
Reply with quote  #3 
I live in sunny Cornwall in the South West of England.
SolarInterested

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Reply with quote  #4 
Most DIY systems documented here preheat the cold water input to a water heater rather than water in the heater itself. I'm not sure of what problems might be specific to the design you want to build so can't really offer any constructive advice. Hopefully someone else can.
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Both temperature rise and airflow are integral to comparing hot air collectors
rcflyers

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Posts: 4
Reply with quote  #5 
Quote:
Originally Posted by SolarInterested
Most DIY systems documented here preheat the cold water input to a water heater rather than water in the heater itself. I'm not sure of what problems might be specific to the design you want to build so can't really offer any constructive advice. Hopefully someone else can.


Ok, thanks.
but the water would only be preheated if the normally cold water is moving into the water heater through the solar panel, if no hot water was being used during the day when we are out at work, then no solar heated water would flow into the tank.
It would just sit there in the panel all day.
SolarInterested

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Reply with quote  #6 
rcflyers you can get an idea of the DIY design I referred to at
http://www.n3fjp.com/solar/BigProject/BigProject.htm
and more at
http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm#Example1KSystems

In these the potable water is kept separate from the water (or antifreeze solution) circulated through the panels and an unpressurized storage tank. The system circulates fluid through the panels until a maximum preset temperature is reached in the storage tank.

A heat exchanger in this storage tank heats the potable water on it's way to the domestic hot water tank. In most cases the heat exchanger is a simple inexpensive coil of PEX pipe. Complete details are in the links above.

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Both temperature rise and airflow are integral to comparing hot air collectors
rcflyers

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Posts: 4
Reply with quote  #7 
Thanks,
I understand that it is easy to heat the water in the storage tank but the domestic hot water tank will not get hot unless you are demanding water from it and flowing incoming cold water through the storage tank.
During the day when we are out the storage tank will get hot but the domestic hot water tank won't see any of that heat.
Our boiler is set to come on just before we get home from work to heat up the domestic tank ready for us to have a shower in the evening hence the need to heat the domestic hot water tank during the day using the solar heated water.

2 more questions:

What size do the pipes need to be between the solar panel and pump etc to allow for adequate drain back when the pump stops?

How can I get the pipes to enter under the roof tiles neatly?

Thanks again for any help.
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