Mixing a combi boiler with "wet" solar panels
 

Hi,

I have bought a small two and a half bedroom end-of-terraced
Victorian house. It has gas central heating with a floor-standing
boiler that does the job. The boiler could be 20 - 25 years old. The
system has a hot water tank with a jacket that seems as thick as a
cardigan. The system supplies loads of hot water and some of the rads
are absolutely scorching. I'm sure the rads could do with a "re-
balance". I feel it is all very inefficient in fuel terms but it works
and will cost a pretty penny to replace.

I'm thinking about doing / getting done kitchen, bathroom and loft.

I would like to stick some "wet" solar panels on the roof, even if
they don't pay off financially, so I feel I am doing my "bit" for the
environment. OK, money does come into it - see below.

At most, the house will be occupied by one or two people. So here is
the idea. Replace the boiler with a condensing combi boiler. Then I
get hot water "on-demand" and at mains pressure. I don't heat a tank
and then let it cool for hot water I never use. I had a Vaillant combi
boiler in a one-bedroom ground floor flat and (apart from the
occasional wobbly) it would chuck out hot water at mains pressure
within seconds. I want to retain that and avoid shower pumps and
electric shower heaters.

The "clever" bit would be to have a hot water tank but only use it
for the central heating. It would have two supply circuits, one from
the wet solar panels on a south-facing roof - this would "pre-heat the
water. The second supply circuit would be from the boiler. The idea
being I could collect as much heat as possible on a sunny day on the
solar circuit and top it up with gas-heated water. The tank would need
to be well-insulated to store the heat from a sunny day and release it
in the evening.

Could such a setup be installed and would the heat gained from the
panels be worth the expense of the installation? Is there anyway of
making a rough calculation on the heat / temperature gain to work out
the money saved on pre-heating the water in the tank?

Thanks

Clive

Mixing a combi boiler with "wet" solar panels
 

Clive wrote:
Hi,

I have bought a small two and a half bedroom end-of-terraced
Victorian house. It has gas central heating with a floor-standing
boiler that does the job. The boiler could be 20 - 25 years old. The
system has a hot water tank with a jacket that seems as thick as a
cardigan. The system supplies loads of hot water and some of the rads
are absolutely scorching. I'm sure the rads could do with a "re-
balance". I feel it is all very inefficient in fuel terms but it works
and will cost a pretty penny to replace.

I'm thinking about doing / getting done kitchen, bathroom and loft.

I would like to stick some "wet" solar panels on the roof, even if
they don't pay off financially, so I feel I am doing my "bit" for the
environment. OK, money does come into it - see below.

At most, the house will be occupied by one or two people. So here is
the idea. Replace the boiler with a condensing combi boiler. Then I
get hot water "on-demand" and at mains pressure. I don't heat a tank
and then let it cool for hot water I never use. I had a Vaillant combi
boiler in a one-bedroom ground floor flat and (apart from the
occasional wobbly) it would chuck out hot water at mains pressure
within seconds. I want to retain that and avoid shower pumps and
electric shower heaters.

The "clever" bit would be to have a hot water tank but only use it
for the central heating. It would have two supply circuits, one from
the wet solar panels on a south-facing roof - this would "pre-heat the
water. The second supply circuit would be from the boiler. The idea
being I could collect as much heat as possible on a sunny day on the
solar circuit and top it up with gas-heated water. The tank would need
to be well-insulated to store the heat from a sunny day and release it
in the evening.

Could such a setup be installed and would the heat gained from the
panels be worth the expense of the installation? Is there anyway of
making a rough calculation on the heat / temperature gain to work out
the money saved on pre-heating the water in the tank?

Thanks

Clive


Well, you could stick an old radiator on the roof as here

http://www.diydata.com/projects/sola..._collector.php

That might pay for itself.
If you're serious, I'd look at prices in Greece where these things are
on every holiday home and are bound to be a good deal cheaper

Mixing a combi boiler with "wet" solar panels
 

On 27 Mar 2007 06:04:18 -0700 someone who may be "Clive"
wrote this:-

I have bought a small two and a half bedroom end-of-terraced
Victorian house. It has gas central heating with a floor-standing
boiler that does the job. The boiler could be 20 - 25 years old. The
system has a hot water tank with a jacket that seems as thick as a
cardigan. The system supplies loads of hot water and some of the rads
are absolutely scorching. I'm sure the rads could do with a "re-
balance". I feel it is all very inefficient in fuel terms but it works
and will cost a pretty penny to replace.

Yet you go on to suggest an expensive to buy and complicated boiler.

At most, the house will be occupied by one or two people. So here is
the idea. Replace the boiler with a condensing combi boiler. Then I
get hot water "on-demand" and at mains pressure.

You can get mains pressure hot water, heated on demand, by using a
thermal store.

I don't heat a tank
and then let it cool for hot water I never use.

Yet you go on to suggest using a hot water cylinder for
"pre-heating".

I had a Vaillant combi
boiler in a one-bedroom ground floor flat and (apart from the
occasional wobbly) it would chuck out hot water at mains pressure
within seconds.

A thermal store will do that.

I want to retain that and avoid shower pumps and
electric shower heaters.

No shower pumps or electric heaters with a thermal store. Note also
that gravity hot water systems don't need them either, as one can
fit a venturi shower.

The "clever" bit would be to have a hot water tank but only use it
for the central heating. It would have two supply circuits, one from
the wet solar panels on a south-facing roof - this would "pre-heat the
water. The second supply circuit would be from the boiler. The idea
being I could collect as much heat as possible on a sunny day on the
solar circuit and top it up with gas-heated water. The tank would need
to be well-insulated to store the heat from a sunny day and release it
in the evening.

Solar heating is necessarily a relatively slow process, as solar
radiation is diffuse. Thus it involves capturing heat over
relatively long periods. This then needs to be stored.

In this situation I would consider using a thermal store which is
heated by a solar panel on a separate circuit and the existing
boiler heating the shell water (until it dies, then replace with a
condensing boiler). Heating would be taken from the shell by a
separate pump. Hot water would be generated from a coil in the
thermal store, or plate heat exchanger if you are in a hard water
area.

Cost depends on how much you do yourself.
http://www.navitron.org.uk/solar_collector_panel.htm is a reasonable
place for some DIY equipment.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

Mixing a combi boiler with "wet" solar panels
 

On 27 Mar, 14:04, "Clive" wrote:

Hi,

I have bought a small two and a half bedroom end-of-terraced
Victorian house. It has gas central heating with a floor-standing
boiler that does the job. The boiler could be 20 - 25 years old. The
system has a hot water tank with a jacket that seems as thick as a
cardigan. The system supplies loads of hot water and some of the rads
are absolutely scorching. I'm sure the rads could do with a "re-
balance". I feel it is all very inefficient in fuel terms but it works
and will cost a pretty penny to replace.

I'm thinking about doing / getting done kitchen, bathroom and loft.

I would like to stick some "wet" solar panels on the roof, even if
they don't pay off financially, so I feel I am doing my "bit" for the
environment. OK, money does come into it - see below.

At most, the house will be occupied by one or two people. So here is
the idea. Replace the boiler with a condensing combi boiler. Then I
get hot water "on-demand" and at mains pressure. I don't heat a tank
and then let it cool for hot water I never use. I had a Vaillant combi
boiler in a one-bedroom ground floor flat and (apart from the
occasional wobbly) it would chuck out hot water at mains pressure
within seconds. I want to retain that and avoid shower pumps and
electric shower heaters.

The "clever" bit would be to have a hot water tank but only use it
for the central heating. It would have two supply circuits, one from
the wet solar panels on a south-facing roof - this would "pre-heat the
water. The second supply circuit would be from the boiler. The idea
being I could collect as much heat as possible on a sunny day on the
solar circuit and top it up with gas-heated water. The tank would need
to be well-insulated to store the heat from a sunny day and release it
in the evening.

Could such a setup be installed and would the heat gained from the
panels be worth the expense of the installation? Is there anyway of
making a rough calculation on the heat / temperature gain to work out
the money saved on pre-heating the water in the tank?

Thanks

Clive


As David explained, you cant lose the water storage and go solar - not
unless you put in solar batch heaters, which are storage and panel in
one.

Combis are not something to choose unless you have no other option.
Performance is poor.

A big storage tank would enable boiler heating of the top half, vacuum
tube heating of top half, and flat panel heating of bottom half.

Some more info:
http://wiki.diyfaq.org.uk/index.php?title=Solar_Thermal

Another good payback energy saver is
http://wiki.diyfaq.org.uk/index.php?...Heat_Exchanger

And of course you need proper tank insulation.

With a heatbank you dont need to replace the tank, as an inbuilt
exchanger isnt needed.


NT

Mixing a combi boiler with "wet" solar panels
 

wrote in message
oups.com...
On 27 Mar, 14:04, "Clive" wrote:

Hi,

I have bought a small two and a half bedroom end-of-terraced
Victorian house. It has gas central heating with a floor-standing
boiler that does the job. The boiler could be 20 - 25 years old. The
system has a hot water tank with a jacket that seems as thick as a
cardigan. The system supplies loads of hot water and some of the rads
are absolutely scorching. I'm sure the rads could do with a "re-
balance". I feel it is all very inefficient in fuel terms but it works
and will cost a pretty penny to replace.

I'm thinking about doing / getting done kitchen, bathroom and
loft.

I would like to stick some "wet" solar panels on the roof, even
if
they don't pay off financially, so I feel I am doing my "bit" for the
environment. OK, money does come into it - see below.

At most, the house will be occupied by one or two people. So here
is
the idea. Replace the boiler with a condensing combi boiler. Then I
get hot water "on-demand" and at mains pressure. I don't heat a tank
and then let it cool for hot water I never use. I had a Vaillant combi
boiler in a one-bedroom ground floor flat and (apart from the
occasional wobbly) it would chuck out hot water at mains pressure
within seconds. I want to retain that and avoid shower pumps and
electric shower heaters.

The "clever" bit would be to have a hot water tank but only use
it
for the central heating. It would have two supply circuits, one from
the wet solar panels on a south-facing roof - this would "pre-heat the
water. The second supply circuit would be from the boiler. The idea
being I could collect as much heat as possible on a sunny day on the
solar circuit and top it up with gas-heated water. The tank would need
to be well-insulated to store the heat from a sunny day and release it
in the evening.

Could such a setup be installed and would the heat gained from
the
panels be worth the expense of the installation? Is there anyway of
making a rough calculation on the heat / temperature gain to work out
the money saved on pre-heating the water in the tank?

Thanks

Clive


As David explained, you cant lose the water storage and go solar - not
unless you put in solar batch heaters, which are storage and panel in
one.

Combis are not something to choose unless you have no other option.
Performance is poor.

A big storage tank would enable boiler heating of the top half, vacuum
tube heating of top half, and flat panel heating of bottom half.

Some more info:
http://wiki.diyfaq.org.uk/index.php?title=Solar_Thermal

Another good payback energy saver is
http://wiki.diyfaq.org.uk/index.php?...Heat_Exchanger

And of course you need proper tank insulation.

With a heatbank you dont need to replace the tank, as an inbuilt
exchanger isnt needed.


NT


I will say it again, very simple system, using a Geldhill Torrent RE Thermal
Store. see www.gledhill.net for more info.

--
Regards

Stephen Dawson
Fox Electrical Services Ltd
www.foxelectrical.co.uk

Mixing a combi boiler with "wet" solar panels
 

On Mar 27, 2:04 pm, "Clive" wrote:
The "clever" bit would be to have a hot water tank but only use it
for the central heating. It would have two supply circuits, one from
the wet solar panels on a south-facing roof - this would "pre-heat the
water. The second supply circuit would be from the boiler. The idea
being I could collect as much heat as possible on a sunny day on the
solar circuit and top it up with gas-heated water. The tank would need
to be well-insulated to store the heat from a sunny day and release it
in the evening.

So you get the most hot water for heating on the sunniest days when
you are least likely to use it. I think you have it arse about face.
Use solar to augment the hot water which you will use year round.

MBQ

Mixing a combi boiler with "wet" solar panels
 

On 28 Mar 2007 06:46:38 -0700 someone who may be
" wrote this:-

So you get the most hot water for heating on the sunniest days when
you are least likely to use it. I think you have it arse about face.
Use solar to augment the hot water which you will use year round.

Properly designed a solar system will produce almost all the hot
water needed in summer.

In winter it is unlikely to produce more than a small fraction of
the space heating requirement, unless it is grossly oversized for
summer use.

In the spring and autumn it might provide a useful fraction of the
space heating requirement on some days.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

Mixing a combi boiler with "wet" solar panels
 

On 28 Mar, 15:25, David Hansen
wrote:
On 28 Mar 2007 06:46:38 -0700 someone who may be
" wrote this:-

So you get the most hot water for heating on the sunniest days when
you are least likely to use it. I think you have it arse about face.
Use solar to augment the hot water which you will use year round.

Properly designed a solar system will produce almost all the hot
water needed in summer.

In winter it is unlikely to produce more than a small fraction of
the space heating requirement, unless it is grossly oversized for
summer use.

In the spring and autumn it might provide a useful fraction of the
space heating requirement on some days.

If one wants to extend it to space heating, sensible thing is to use
warm air panels for that, as theyre inherently much more efficient,
have a much longer season and cost less.


NT

Mixing a combi boiler with "wet" solar panels
 

So you get the most hot water for heating on the sunniest days when
you are least likely to use it. I think you have it arse about face.
Use solar to augment the hot water which you will use year round.

MBQ

I see where you are coming from. Isn't that the conundrum with any
domestic solar-based heat / energy colleciton in the UK? The
conditions that will lead to "usable" heat from the panels will tend
to be those days when you don't need the space heating. That's why in
my original post I asked about heating water by solar and
supplementing it with gas.However, one always needs hot water, even in
summer for personal washing (unless that isn't your thing) and clothes
washing.

Whether it's financially viable, I don't know. At least I will have
the smug satisfaction of feeling I am "doing my bit" for the
environment. I am sure there is an argument that the energy expended
in manufacturing, transporting and installing the equipment needed for
a "solar-supplemented" system far exceed any marginal savings in gas
burned.

thanks for the link about the "thermal store". That's looks like the
kind of system I might get. Looking at the diagrams and descriptions
it seems broadly similar to what I described in my original post: dual
"heating" circuit from solar and the boiler to "top-up". Substitutue
"tank/cylinder" for thermal store and it seems a similar idea. Anyway,
I now have the right terminology and a potential supplier - so much
thanks for that.

Thanks for the good point challenging the idea of replacing the old
boiler with a combi. With the thermal store, system as I understand
it, the boiler is simply a source of heat to top up the thermal
store.

Oh, I'll ignore the high-handed tone of much of the responses in this
thread. I had a few ideas, I came to this group asking for information
and advice in the knowledge others were better informed, otherwise why
would I come here? The information provided has been very useful to
me. Thank-you. I'll ignore the disparaging tone in which much of the
information was delivered.

Mixing a combi boiler with "wet" solar panels
 

Thanks for the good point challenging the idea of replacing the old
boiler with a combi. With the thermal store, system as I understand
it, the boiler is simply a source of heat to top up the thermal
store.


I also meant to write further, but Windows "sticky keys" got me. If
you have never experienced that, consider yourself lucky.

Anyway.

The thinking behind installing a combi boiler was to achieve instant,
*mains pressure* hot water. The hot water in the house *is* hot (yes,
I have fallen in love with the simple, little to go wrong, 25-year old
boiler). Now, the thermal store literature claims it can deliver
instant, *mains pressure* hot water. I can't understand *how* , since
it's just a cylinder - sorry, thermal store. Won't it need a head of
pressure i.e. loft installation to deliver hot water under pressure?
I'll take that on trust unless anyone can explain how the thermal
store system achieves the mains pressure output?

I can now see that my requirements for heating and hot water are
contradictory. I guess the thermal store approach tries to gather as
much usable heat as it can for both needs to reduce gas (or other
fossil fuel) burned. This thread is helping me understand the options.

BTW, I have looked at that self-built heat-exchanger to reclaim heat
from shower waste and pre-heat the cold supply to the shower. Looks
really neat, simple to manufacture and plumb in - so seems surprising
it's not mass-produced.

Clive

Mixing a combi boiler with "wet" solar panels
 

On 29 Mar, "Clive" wrote:

So you get the most hot water for heating on the sunniest days when
you are least likely to use it. I think you have it arse about face.
Use solar to augment the hot water which you will use year round.

MBQ

I see where you are coming from. Isn't that the conundrum with any
domestic solar-based heat / energy colleciton in the UK? The
conditions that will lead to "usable" heat from the panels will tend
to be those days when you don't need the space heating.

Its often brought up, but is not a problem in reality. The system is
sized to give useful heat for a sizeable amount of the year, and any
excess harvest in midsummer does not cause any real problems.


environment. I am sure there is an argument that the energy expended
in manufacturing, transporting and installing the equipment needed for
a "solar-supplemented" system far exceed any marginal savings in gas
burned.

I think thats true with systems that arent well designed. There are
many about that will never pay their way financially or energy wise.
To get one that does something useful one must properly evaluate the
proposed system first, and try design after design until one proves
good. It will be nice to see the day when this process is no longer
necesary, due to future leaps in performance and economy.


boiler). Now, the thermal store literature claims it can deliver
instant, *mains pressure* hot water. I can't understand *how* , since
it's just a cylinder - sorry, thermal store. Won't it need a head of
pressure i.e. loft installation to deliver hot water under pressure?
I'll take that on trust unless anyone can explain how the thermal
store system achieves the mains pressure output?

The hot water outlet connects to the incoming water mains. No header
tank is used. Hence its still at mains pressure. Its made hot along
its travel by going through a heat exchanger. The tanked hot water is
an entirely separate body of water that just heats the heat exchanger
plates.

The downside of this is fouling of the heat exchanger, hence the need
to use an exchanger with much higher power rating than will be needed
initially.


BTW, I have looked at that self-built heat-exchanger to reclaim heat
from shower waste and pre-heat the cold supply to the shower. Looks
really neat, simple to manufacture and plumb in - so seems surprising
it's not mass-produced.

Clive

Good question, why isnt it?

Its not fitted at new buid because its an unnecessary cost to the the
builder and house buyer, and isnt required by regs yet. Also few house
buyers even know about them so far.

Its not diy retrofitted because its too much upheaval/work for limited
gain.

So there isnt much of a market at present. With increasing drive to
get better energy efficiency I daresay they;ll become required some
time soon.


NT