Indirect Solar System Q?

[cozy]

Hi Can anyone help me understand how to do the following -

I want to pick up the hot water feed from the boiler (in garage) and route it through the spare currently unused coil in my cylinder, then once the hot water has passed through the coil return it on it's journey to the rads. I understand that there's a thermostat needed at the tank and motorised valves needed - but not sure how many and exactly what their purpose is? I've routed 22mm copper up to, and down from the cylinder to the boiler but not connected. I also need to know what power cable needs to connect the thermostat to the mv's? if this makes sense? The cylinders primary source of energy is solar backed up by emersion. Thanks!

 

[Renewable M]

Ok so you want to use the boiler coil in the cylinder for its intended purpose.

Cool, you need to be able to control the on off of the boiler so that it doesnt try to get too much heat into the cylinder. That's where a timer, cylinder thermostat and valve come in. They provide the control by means of time and temp.

Make sure your solar is connected to the bottom coil in the cylinder too, by the way.

I assume that what you are trying to achieve is this: http://www.ecoairsource.com/air-source-technical/Basic Solar Thermal Schematic.pdf but with rads too.

Basically, between the boiler and cylinder are the timer, valves controlled by room stat and cylinder stat.

Look up a diagram for y plan and that'll clarify everything.

hope it goes well.

bear in mind you need a legal sparky.

 

[cozy]

Brilliant RM - Thanks for getting back to me so quick - I'll check out the link. The way it was explained to me (Some time ago) is that the central heating system was circulating hot water anyway when on (to the rads) so why not divert it through the cylinder on its journey - thereby nicking a bit of heat which in turn would save on the emersion kicking in. So naively I took this as only when the central heating was running?

PS Yes I have a Q'd spark check all I've done.

 

[Renewable M]

cool, no problem.

You're kind of right about circulating the water through the coil, it just needs its own kind of mini circuit, as i mentioned for control (it meets building regs than and makes good sense)

So the boiler can come on just for the radiators, just for the cylinder, or for both depending on your timer and stats.

The immersion may not be a big baddie though.

Here we go.... an immersion typically 3kw. So used 3 x 1kw.h of electricity on an hour. So to raise for example a 200 litre cylinder by 30 degrees, would require 200 x 30 x 0.001164, with the 0.001164 being the kw required to raise 1 litre of water by one degree. (before any system losses)

so, the answer in this example is 6.984kw/h or approx 2 hrs 28 min of your immersion.

You can use the 6.984kw/h and multiply it by the cost of your electricity to see what you can potentially spend on the reheat.

Now, 1 litre of 28 sec kerosene on a good day in your boiler yields 6kw of heat energy. Assuming an HE boiler, correct sizing etc etc which is not generally achieved. Anyway...

Bear in mind that if the boiler is on water heating only is is going like the clappers, cycling and being as inefficient as possible. You have massive losses to system water, the boiler shell and flue and are heating all the water in the boiler and pipes and not recovering this heat in any meaningful way.

If the boiler shell and pipework holds a mere 40 litres, and you heat it from 15 degrees to 75 degrees, that requires wasted energy of 40x60x0.001164 = 2.7936kwh. So half of the energy you need to be transferring into the cylinder is wasted entirely.

So.......the immersion is more than likely the cheapest possible way of replenishing the hot water.

You can work this the other way round for your solar. Cylinder temp in morning, say 35 degrees, cylinder temp at sundown 55 degrees, cylinder volume 200 litres. Thats a 20 degree rise across 200l which is 4.656kh/h of energy transferred into the cylinder by solar gain.

So, with the inefficiencies of the boiler as mentioned, the solar in this case saves you about 40p a day in oil.

If you build in the cost of the components and labour to tie in the oil boiler, it isnt worth doing.

Never invite me to a dinner party. I can bang on like this for ever...

 

[cozy]

Wow! I'll need to take my time to absorb this - I'm on gas for the boiler - besides I've just forked out £100 for 30m of 22mm copper - ( I had to do this because I needed to route the pipes through a bathroom which I'm about to tile ) Hence the Q about what power cables to route also. So it's like I'm committed now! The heating engineer I'd previously spoken to said it would be worth 'tying in' as you put it as long as I did the donkey work myself. I'll get there, but it'll take me a bit of time
Maybe that should be my little saying at the end! - Thanks again

 

[Renewable M]

sorry, where did i get oil from. well for gas it's straightforward. a cubic m (if you are still metered that way) is as anyone will tell you about 11kw/h but most bills are now in straightforward kw/h.

Gas boilers are more efficient and lower water content than oil, as used in my example. So as long as you have the hot water on with the heating, you should do alright.

If you ever need a calculation for how much chocolate you would need to eat to then ride a bicycle to generate electricity to power your home, let me know.

Ahem.......I need to get out more.

 

[cozy]

Funny!- I can tell you how many plain peanut butter sandwiches it takes to run 40 miles with 4,000ft up/down in 8 hours because i just did it!

 

[Renewable M]

Good lad. A former colleague did the dorset jurassic coast supermarathon last year.

where do you run?

 

[cozy]

Last year was my first season of Ultra Marathons I nailed two - Phoenix 33 (Over N.Yorks moors) and The High Peak 40 -(Mam Tor Deepdale etc) I run out of N.Wales and do the Snowdon marathon each year. (Sorry about this plumbers!)

 

[stevetheplumber]

if you situate the two port motorised valve on the pipe close to where you tee of from existing youll need only a wire from the thermostat three core for s plan four core for y plan thats alowing for earths one less each if stat is double insulated

 

[Renewable M]

ace, good stuff. I'm too busy being sick and me knees are less and less interested. so are you mad or did you have to learn to run?

We got a job on over that way for one of our installers, a care home, anglesey. 4 heat pumps and plant room.

I used to stay in Madley, that anywhere near you? 418385

 

[cozy]

I'm getting there quicker than I thought! thanks Steve. Understand the wiring. excuse me on this though - what's s-plan y-plan?

I'm getting there quicker than I thought - Cheers steve - understand the wire requirement - excuse the next Q - What is s-plan y-plan? Also do I only need one motorised vavle ? I assume to open and let flow in?

R - I'm in the Mold area - Mad yes! - Seriously though - had to learn to run that kind of distance - some say I've developed quickly (Non running to Ultra in 2'n half years) Also started with bad knees at 47 - but solved the problem. To save boring non-runners on here - if I can return advice i'd be happy to on Runner's World UK look for Snowdon 2010 thread I'm known as SZ on that.

 

[stevetheplumber]

thinking about this i realised ive yet to see a wireless cylinder stat

 

[Renewable M]

nice one cozy. non running to s.m in 2 yrs! You must have really had your head on for that.

sorry, forgot to mention the wireless cylinder stat.

Danfoss Randall CET B-RF Wireless is just the job. about 80 quid and worth its weight in gold.

 

[cozy]

Wireless stat - why not!

 

[Renewable M]

Here's a rough schematic for your heating, a simple y plan, with your solar and remote room and cylinder stats.

It's just meant to illustrate the general layout.

here

 

[cozy]

Thanks for all your kind advice - that last plan is where I need to be - I'll be doing a bit on it this weekend.