PowerSwitch

Posted: **21 Jul 2008, 21:08**

Finally had the quote through. Would really appreciate comments:
Background - combi in garage, thermal store to go in loft so I can
plumb in the store with back boiler later. Cost 5K
Have a schematic in jpeg - how do I upload it?

The setup revolves around a heatstore as discussed that will accept
inputs from the various sources:

QUOTE:

* Solar (via pressurised coil)
* Log burner (direct thermo-siphon)
* Combi boiler (via pressurised coil)
* Immersion heater

And outputs to:

* DHW via heat exchanger coil and temperature blending valve
providing mains pressure hot water
* Central heating (direct pumped)

Operation

During the summer, heat demand will be for domestic hot water (DHW).
This should normally be satisfied by the solar heater. However it would
be prudent to have the immersion heater active for an hour or two after
dark to bring the top of the cylinder up to temperature if the day has
been cloudy.

During the winter, heat demand will be for central heating (CH) drawing
heat from the centre of the cylinder and DHW. Primary heat input will be
from the combi boiler operating via a thermostat on the cylinder
maintaining the temperature of the upper 2/3 of the cylinder at 60deg
when timed to.

When the log burner is in use, heat will be transferred to the cylinder
via a thermo siphon circuit in the bottom of the cylinder. This area of
the cylinder will also be pre-heated in the winter on sunny days by the
solar heater.

Although connections will be fitted to the heatstore, I have not allowed
for connecting,

Quotation

To carry out installation as described below at:

my gaff

* Supply and install one 259 litre triple insulated heatstore
fitted with one 3kW immersion heater and temperature blending valve into
the loft.
* Supply and install one feed & expansion tank. May be combined
onto heatstore
* Supply and install one 30 tube 47x1500mm solar collector onto
the pitched roof at the front of the house and connect to heatstore
* Supply and install one solar pump station, controller and
expansion vessel.
* Supply and install pipe work from the heatstore to the first CH
microbore manifold.
* Extend mains water into loftspace.
* Supply and install pipe work from the boiler to the heatstore.

£5,000.00 including VAT

Not included as part of the quotation:

* Works to facilitate access for the cylinder into the loft if
required.

* Pipe work and control for the log burner which I assume you
will have carried out by a specialist contractor.

* Two fused mains spurs in the loft; one for the solar control
and one for the immersion heater.

* Making good or boxing in of any pipework left exposed after
completion.

* Boiler re-commissioning by a CORGI registered heating
engineer.

If you have any queries or would like to discuss this quotation any
further, please do not hesitate to call me.

Best regards

Posted: **21 Jul 2008, 21:15**

JonB wrote: Have a schematic in jpeg - how do I upload it?

Unfortunately not that simple. You cant upload it directly to powerswitch. You need to open an account with one of the free online image storage sites, upload the image to that site, then copy its URL and paste that into the post, select, then add 'img' tags provided by the 'Img' button on the message editing page.

Clear as mud?

I use http://picasaweb.google.com/ to store images online. Gives you a gigabyte of free image storage.

Its good etiquette not to post images that are too large or too heavy. some people still have low resolution monitors which will not be able to show the whole of large images, and some only have dialup connection - heavy images (ultra high quality, low cmpression = lots of Mb) gives them a very slow page load time - boring!

If possible use an image editor to increase the JPEG compression as much as possible to just below the point where image quality starts to become unacceptable. In Photoshop, should you have it, there is a command called "Save for Web & Devices" which is ideal for optimising web images.

Optimising images by scaling down and recompressing also helps with Powerswitch's bandwith usage costs. Everytime you view a page at Powerswitch, somebody is paying for it! (My avatar, for example is only 2478 bytes)

Only ever use GIF or JPEG for viewing online.

Posted: **21 Jul 2008, 22:23**

skeptik wrote: Only ever use GIF or JPEG for viewing online.

Or PNG for charts works very well!

Posted: **21 Jul 2008, 22:48**

Hope this works:

Posted: **21 Jul 2008, 22:50**

JonB wrote:Hope this works:

damn.

What am I doing wrong? Got it down to 94K - assume that is OK?

Posted: **21 Jul 2008, 22:53**

here you go..

Posted: **21 Jul 2008, 23:05**

The image isn't loading for me at dialup speed with one bar on my mobile phone. Oh the joys of being in rural Wales!

Anyway, that's a lot of weight to go in the loft. Has it been taken into account? Solar installers are likely to be plumbers and electricians, not structural engineers, and I think you'd like it to stay in the loft!

Posted: **22 Jul 2008, 00:00**

You can see the image if you go to
http://lh3.ggpht.com/jonbrewis.brewis/S ... ematic.JPG

but there seem to be a few things wrong. You won't get more than a small jug full of hot water from your hot tap, for instance.

Posted: **22 Jul 2008, 07:04**

biffvernon wrote:You can see the image if you go to
http://lh3.ggpht.com/jonbrewis.brewis/S ... ematic.JPG

but there seem to be a few things wrong. You won't get more than a small jug full of hot water from your hot tap, for instance.

Why? The thermal store coil for the HW was one of the things I was more sure of....(head hurts)

Posted: **22 Jul 2008, 07:52**

Unless I've read the diagram wrongly, cold water from blue arrow 'Mains in' flows to coil in hot end of tank and then to your tap via red arrow 'To Taps'. It takes a little while for the heat to transfer through the coil and after the 'small jugful' of hot water that has been sitting in the coil when you turn your hot tap on the cold water will only be in the coil for a few seconds as it flows through. It will come out almost as cold as it went in.

You have to have the hot taps fed from the bulk of the water in the tank. But you don't want the water in the 'Heating Circuit' coming from the same source. That can come directly from the boiler.

Posted: **22 Jul 2008, 08:25**

Hey, Biff, that is exactly how a thermal heat store works. It takes heat from the tank and heats mains pressure water via a high surface coil. It means you have pottable high pressure (mains pressure) hot water.

I went through this last year JonB. In the end I chose to go for a standard tank with 4 coils in it. From bottom up I have Solar Coil, Rayburn Coil (28mm), Gas boiler coil and at the top a take off coil for our radiators. All coils are independent. Hot water is drawn of the main tank and is not pottable, this means it is all so unpressured, and does not need certification all the time like a pressurised thermal heat store. My tank functions as a thermal heat store, but doesn't provide mains pressure hot water! It was also much cheaper (newark copper cyclinder company supplied it - you can specify exactly what you want and they make it to order).

The drawbacks I saw to the thermal heat store were:
1/ You need mains water supply to obtain hot water. - if you ever wanted to harvest rain water for DHW it would be trickyer if it had to be supplied on demand at mains pressure.
2/ It needs a plumber who can certify it (more costly).
3/ It cost more.

I had the tank fitted, the rayburn fitted (including costly flu) and the gas boiler was there already, but needed taking off the old tank and reconnecting.

I think I got the whole lot done for under £3k.

Posted: **22 Jul 2008, 08:30**

biffvernon wrote:Unless I've read the diagram wrongly, cold water from blue arrow 'Mains in' flows to coil in hot end of tank and then to your tap via red arrow 'To Taps'. It takes a little while for the heat to transfer through the coil and after the 'small jugful' of hot water that has been sitting in the coil when you turn your hot tap on the cold water will only be in the coil for a few seconds as it flows through. It will come out almost as cold as it went in.

You have to have the hot taps fed from the bulk of the water in the tank. But you don't want the water in the 'Heating Circuit' coming from the same source. That can come directly from the boiler.

This may be a problem, it depends on the design of the coil.
If the coil was designed for heating up the tank from a boiler or solar thermal system, then the rate of heat transfer will be too slow and the water from the hot tap will at best lukewarm.
If however the coil was designed for heating cold mains water, from the low pressure hot water in the tank, then it should be fine, the coil will have been designed with a much great surface area to allow very rapid heat transfer.

Posted: **22 Jul 2008, 09:34**

There was a discussion on the Green Building Forum about it that could help. I Googled thermal store heat exchanger and came up with some sites that explain thermal stores, but didn't check them properly due to my slow internet connection.

Posted: **22 Jul 2008, 11:33**

Cant see the jpg given above.

A description of our heatstore system follows , with some ramblings.

We live in a so called "chalet style" detached which originally
had a coal fire driven CH and DHW with gravity fed pipes to a primatic
(or fortic?) tank on the landing . I replaced the coal fire source with a
gas boiler and that was ok till the boiler carked it .
Always thought that the primatic was an unhealthy concept relying
on an air bubble to separate the 'dirty' water from the DHW.

Dont have real access to our loft (cut a hole in the landing ceiling to
investigate) , but iirc , it has 4x2s as the standard joist ie not feasible
to walk on. and did not feel they were strong enough for a large tank.
Eventually I decided to put in a heatstore (on the landing) , and sometime
later got a replacement boiler put in.

The heatstore has a header tank sat on top and that is open ie it is a
low pressure system (18inch dia , maybe 5ft for the tank and 1 ft for
the header tank?) .
The installed boiler is a 60000btu ... is that 8kwh? whatever.

The key features are

Code: Select all

-  there are no coils inside the cylinder                          

-  the water in the heatstore is connected to the rads and the boiler
       ie 'dirty'  . So to turn the CH on , then the rad pump is turned on
       &#40;assuming that the boiler is already on&#41; and that pumps the
       cylinder water round the rads .     The tank to rad is in the middle
       of the tank , and the return is at the bottom of the tank, so it
       circulates the water round the bottom half of the tank.

-  a heat exchanger is mounted externally &#40;on the front&#41; to provide DHW ,
      it has hot water from the upper part of the tank pumped thru
      one side when a a flow sensor , mounted in the DHW supply  
      detects demand.  The mains cold water feeds the other side of the
      exchanger .  There is also a thermo mixer valve that
      can be set to give whatever temp wanted for the DHW.
      The tank input to the exchanger is near the top of the tank,
      and the return is to the middle ie it uses just the top half of the tank.

                                                                     
-  the other 'luxury' feature is a mixer valve , used to feed back
      boiler water , back to the boiler , so it comes out hot 
      into the tank , which the bloke said was mainly useful 
      for old heavy boilers . However this is a modern light one.
      It does make the heating time for a shower quite quick as dont need
      all the cylinder to be heated to take a shower &#40;in the summer&#41;.

-  if want a bath or shower and the rads to be on , then need a longer wait
      to get the whole tank heated up and if then turn on the rads &#40;pump&#41;

-  could not put radiators higher than the header tank, but there is no need
        for that .

problems I have had :

Code: Select all

-  ball valve to allow automatic topping up went in short order &#40;twice&#41;
   so now manually fill it up -  whenever I hear odd noises &#58;-&#41;
-  the boiler feed back thermo valve , started 'singing' and took
   quite a lot of messing about before I got it quiet ... have a replacement
   valve but it is a pita draining down the system to do that job .

pros/cons of this sort of heat store ...

Code: Select all

-  mains pressure hot water  , clean - direct from the cold mains
      &#40;not like the traditional uk system , giving low pressure
      DHW from a  potentially dirty tank in the loft &#41;.
-  fairly fast DHW from cold , due to recirculating mixer valve
      altho a hi power boiler would probably do the same.
-  turning on the CH,  pumps the hot water out of the cylinder ,
      and vv pumps the cold water in the rads and pipes back into the
      tank presumably cooling it down .... this is something that
      I am aware of but not sure how big a problem this actually is .
-  think that you need to ensure that the size of cylinder is large
      enough to fill the bath &#40;comfortably&#41; , or to heat the difference
      whilst the water for the bath is running.
      This is true I guess for all traditional systems anyway .

bought it from heatweb who were very helpful before I bought it and the odd
time when I have contacted them since . A look on their web site
shows some integrated solar systems (havent checked them out) ...
might be worth your while having a look to see if any come close to yours
and then ring them up and have a chat .

I have thought about doing solar hot water , but think that for my setup
that would probably want a separate tank + mixer valve to heat the
cold mains water , which feeds the DHW heat exchanger/mixer valve system,
ie not cold any more but a warm/hot feed ? Not sure how much sense
that would make ? but seems a lot messier than I would like , esp the
extra tank that would need topping up.
I have a tendency to over engineer things , so it might be possible to
do this more simply ... and when/if I come to do it, then I would
have a look at the heatweb systems for ideas.

Looking at your system details , the solar heats the tank by the
pressurised coil . Maybe need a checkvalve on that to stop
the tank from heating your solar array .
I dont understand why it says that would use the immersion heater to top
up the hot water and not the boiler .

As you say , the tank will need strong supports for the weight
(259L -> 259kg -> 40 stone or 1/4 ton ruff calcs).
My loft had 4x2s , but another loft I know has 7x2s (maybe 7x3?)
and would be strong enough if near the ends (I think).

One standard system I know has gravity pipes (1 1/2 inch ?) heating the
cylinder , but the p*llock that installed it (a long time ago) has cut
massive chunks out of the joists in the bedroom (no dancing in that bedroom!),
whereas a pumped system would use 3/4 inch and have been better .

I dont know enough to really comment on the pricing etc .

enough rambling for now ,

Steve

Posted: **22 Jul 2008, 21:55**

Thanks for this. Obviously need to do some more digging.

Thanks again.

Now, to work out how to get the pictures to work....

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