DIY wiki: Increase Hot Water Capacity

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John Stumbles

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Feb 6, 2008, 7:26:50 PM2/6/08
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There's an article of that title that's appeared on the wiki
http://wiki.diyfaq.org.uk/index.php?title=Increase_Hot_Water_Capacity

"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
Does the hot water run out too soon?
7 ways to increase hot water capacity
=====================================

Bigger Tank
-----------
The obvious option is a bigger tank. Thankfully there are easier ways too.

Higher Thermostat Temperature
-----------------------------
The simplest way to increase capacity is to turn the HW thermostat up. This
means the hot water is used more slowly, as less of it is needed to bring
the shower or bath upto the required temp. Thus your HW lasts longer.

Taking this method to extremes, setting the stat to 95C gives a lot more
hot capacity, but high temperatures are a serious burn risk, and best
avoided.

Drain Heat Exchanger
--------------------
A lot of heat goes down shower drains. Nearly the entire contents of the
hot water tank in fact.

A Drain Heat Exchanger recovers a good percentage of this heat, returning
it to the shower cold feed. So less hot water is needed to bring it upto
temp, and the tankful lasts longer.

By reducing energy use these exchangers can pay back their cost in under a
year in some cases. For information see the main Drain Heat Exchanger
article.

Move Thermostat Lower
---------------------
HW tank thermostats are typically 2/3 the way down the tank, but are
sometimes higher up. HW tanks heat up from the top downwards, and water
below the stat will be at lower temp than the stat setting. Often this
cooler water is no more than lukewarm, and this could be heated to gain
more HW capacity.

Moving the thermostat further down will increase the quantity of hot water
in the tank. The implications depend on where the stat is in relation to
the heating element or built in exchanger.

* If the stat was high up and is moved to 2/3 down, things will behave
normally after moving
* If the stat is moved much lower than the exchanger or element,
heating that extra bottom zone of the HW tank will take longer, and
the top water will get hotter than the stat setting.

Solar Preheater
---------------
A solar preheater produces a batch of warm water which is fed into the tank
when hot water is used, rather than the HW tank drawing cold water in as
happens with most HW tanks. The result is less energy use and to some
extent increased HW output. The amount of output increase will depend on
the temperature of the preheat water.

There are several designs of solar preheater, with performance varying
significantly from one design to another.

With any solar thermal equipment, it is strongly recommended to assess any
proposed system properly before construction, since many designs are
unable to pay back their cost. Professionally supplied systems are worse
than DIY ones in this respect.

Use CH Circuit Heat
-------------------
The Central Heating radiator circuit contains hot water in winter and tepid
Water in summer. It is possible to harvest this heat and add it to the HW,
thereby giving greater HW capacity.

Ways to arrange this:

* With a heat bank or Thermal Store, The cold water supply goes through
a heat exchanger on the CH circuit before going to the HW heat
exchanger.

* With a combi, the cold water supply to the combi goes through the CH
exchanger, thus boosting the heat output for a while.

* With a conventional HW tank, the cold feed to the HW tank goes through the CH
exchanger.

Performance

The Heat bank option uses all the CH heat. It is the most effective option.

How much boost the combi option gives depends on system design and boiler
characteristics. It may prove to be advantageous to restrict the CH heat
exchanger size to ensure the boiler does not modulate at first during HW
heating.

The conventional tank variant can only benefit from part of the CH
circuit's heat capacity. Once the CH circuit drops below usable HW temp,
the remaining heat will not be used in a way that increases HW output at
the tap. Hence there will be no HW boost in summer. Although capacity is
not improved as much, HW recovery times will be improved all year round,
and more so in winter.

Electric Boost
--------------
This one is just an idea for discussion, and has not been tried by the
author. You should not try it without finding out whether it would work ok
first.

Add a 3kW heater to the cold water feed at the shower & bath taps, along
with a low temperature thermostat to avoid uncomfortable temperature rise.

If heater flow is restricted, it may be possible to split the feed into 2
parallel pipes, one that goes through the heater and one that contains an
isolating valve. The 2 feeds are then reunited. Adjustment of the iso
valve determines the flow sharing.

By prewarming the cold feed, less HW is needed, so the tanked HW lasts
longer.

Another variant is to add a 3kW heater to the combi heated water output (or
possibly cold water input), and trigger it by a flow switch on the shower
& bath hot water feed.

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I have some questions which I posted to the article's discussion page:
http://wiki.diyfaq.org.uk/index.php?title=Talk:Increase_Hot_Water_Capacity

However this is probably the better place to discuss them in order to
arrive at a peer-reviewed article so may I invite interested parties to
comment?

--
John Stumbles

Fundamentalist agnostic

Tim Downie

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Feb 7, 2008, 3:33:55 AM2/7/08
to
John Stumbles wrote:
> There's an article of that title that's appeared on the wiki
> http://wiki.diyfaq.org.uk/index.php?title=Increase_Hot_Water_Capacity
>
> """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
> Does the hot water run out too soon?
> 7 ways to increase hot water capacity
> =====================================
> Drain Heat Exchanger
> --------------------
> A lot of heat goes down shower drains. Nearly the entire contents of
> the
> hot water tank in fact.
>
> A Drain Heat Exchanger recovers a good percentage of this heat,
> returning
> it to the shower cold feed. So less hot water is needed to bring it
> upto
> temp, and the tankful lasts longer.

I suppose it depends on how long you spend in the shower but I'd have
thought that by the time the water has flowed over your body, the shower
cabinet, the wall tiles & the shower tray, the amount of usefully
recoverable heat left in what's going down the drain isn't a great deal.
Besides, if my daughters knew I had a heat saving device they'd just shower
for longer. ;-)

Tim


meow...@care2.com

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Feb 7, 2008, 9:41:04 AM2/7/08
to

Where else would most of that 7-24kW go? How hot do the tiles get :)


NT

Ed Sirett

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Feb 7, 2008, 4:19:38 PM2/7/08
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I just foolishly deleted a long reply.
I CBA to do it again. so I'll summarise and be much less diplomatic (but
still above the DD level I hope).

Bigger tank - of course but that other ideas are trying to solve not
obliterate the problem.

Up the temp. 65C or use blending valve with 75C+boiler(85C) or electric
85C.

Drain H.E. Might put restriction on cold feed to HW. Only helps showers.

Move t/stat lower: I guess 1/4 is lowest practical?

Solar preheat: Even more marginal that solar assist. Also solar panels
need to be drain back or anti freeze.

Extract from Primary circuit: In winter robbing the radiators will be
counter productive (especially with a combi system). In summer there
should not be very much hot primary water on hand.

Add 3kW of electric: this adds 12.5% (on the lowest 24kW combi) and
lesser on anything bigger including a stored system.

Could try:
1) restrict HW flow where it's not so needed eg. wash basin
2) Change usage and heating patterns.
3) Upgrade to cylinder with faster coil.
4) Down grade boost pump.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

Andy Hall

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Feb 7, 2008, 4:31:02 PM2/7/08
to
On 2008-02-07 00:26:50 +0000, John Stumbles <john.s...@ntlworld.com> said:


John Stumbles

Fundamentalist agnostic

=====


I've always thought of myself as a militant apathetic.


Onetap

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Feb 7, 2008, 6:29:30 PM2/7/08
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On 7 Feb, 00:26, John Stumbles <john.stumb...@ntlworld.com> wrote:
> There's an article of that title that's appeared on the wikihttp://wiki.diyfaq.org.uk/index.php?title=Increase_Hot_Water_Capacity


It's our Nigel again.
He has delusions of expertise and is liable to get the hump with
anyone who has the audacity to suggest that maybe some of his
proposals are not a very good idea.


> Bigger Tank

Yeah.

> Higher Thermostat Temperature

Scald risk, much higher standing energy losses. A lot more limescale
deposits itself at higher temperatures. The usual recommendation,
borne out of hands-on experience, is 60 degC storage.

> Drain Heat Exchanger
> --------------------
> A lot of heat goes down shower drains. Nearly the entire contents of the
> hot water tank in fact.

I am sceptical. You'd need a tube-in-shell heat exchanger and these
are becoming unusual because of the cost of copper. A plate heat
exchanger is impractical due to fouling and primary-side resistance.
Plastic's thermal conductivity makes it implausible. The fouling
factor would be huge and it would require frequent cleaning to remove
the hair, soap scum, pubes, urine, etc.. You'd also have stagnant
water on the secondary side when not in use, warmed to blood heat when
it was and a risk of contamination from the drains to the mains. So,
having constructed a legionella breeding incubator, you spray the
water out of a shower. Sounds great.

They've never been sold commercially. I wonder why?

> Move Thermostat Lower

Similar to turning the thermostat up. Higher standing losses, scald
risk, limescale accumulations.


> Solar Preheater
> ---------------
> A solar preheater produces a batch of warm water which is fed into the tank

Storing warm water is not a good idea. It is verboten. You could be
excommunicated from CIBSE, your slide-rule broken before your eyes and
your silk tie cut into small pieces.

Just get a solar water heating system which stores hot water. But it
needs a storage cylinder, a big one.

> Use CH Circuit Heat
> -------------------
> The Central Heating radiator circuit contains hot water in winter and tepid
> Water in summer. It is possible to harvest this heat and add it to the HW,
> thereby giving greater HW capacity.

No, it contains hot water in winter that's needed for heating. If it
contains tepid water in summer, there's something wrong with it.


>     * With a heat bank or Thermal Store,

A thermal store? Why not store the therms in a bigger DHWS tank? I
must be missing something.

> The cold water supply goes through
>     a heat exchanger on the CH circuit before going to the HW heat
>     exchanger.

>     * With a combi, the cold water supply to the combi goes through the CH
>     exchanger, thus boosting the heat output for a while.

All the boiler water gets diverted to the DHWS heat exchanger. You
can't utilise the heat going to the CH circuit because when there's a
DHWS demand, there isn't any. The combi CH usually goes off while you
run the hot water.

Just get a modern cylinder. The coil is nearer the bottom, it heats up
quicker and the insulation is better.
Or turn your home into a water heating laboratory. SWMBO will like
that.

Doctor Drivel

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Feb 7, 2008, 6:43:00 PM2/7/08
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"Tim Downie" <timdow...@obviousyahoo.co.uk> wrote in message
news:60vu3kF...@mid.individual.net...

They do work and pay for themselves.

Doctor Drivel

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Feb 7, 2008, 6:45:46 PM2/7/08
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"Ed Sirett" <e...@makewrite.demon.co.uk> wrote in message
news:fofsla$hs$2$8300...@news.demon.co.uk...

> I just foolishly deleted a long reply.
> I CBA to do it again. so I'll summarise and be much less diplomatic (but
> still above the DD level I hope).
>
> Bigger tank - of course but that other ideas are trying to solve not
> obliterate the problem.
>
> Up the temp. 65C or use blending valve with 75C+boiler(85C) or electric
> 85C.
>
> Drain H.E. Might put restriction on cold feed to HW. Only helps showers.

There is a bath version. See gfx web site.

Doctor Drivel

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Feb 7, 2008, 6:48:37 PM2/7/08
to

"John Stumbles" <john.s...@ntlworld.com> wrote in message
news:efsqj.2108$nG4...@newsfe6-win.ntli.net...

> Use CH Circuit Heat
> -------------------
> The Central Heating radiator circuit contains hot water in winter and
> tepid
> Water in summer. It is possible to harvest this heat and add it to the HW,
> thereby giving greater HW capacity.
>
> Ways to arrange this:
>
> * With a heat bank or Thermal Store, The cold water supply goes through
> a heat exchanger on the CH circuit before going to the HW heat
> exchanger.

>...

He has been reading my posts on this point..

Doctor Drivel

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Feb 7, 2008, 6:57:51 PM2/7/08
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"Onetap" <one...@talk21.com> wrote in message
news:e823951c-bead-416d...@c4g2000hsg.googlegroups.com...

On 7 Feb, 00:26, John Stumbles <john.stumb...@ntlworld.com> wrote:
> There's an article of that title that's appeared on the
> wikihttp://wiki.diyfaq.org.uk/index.php?title=Increase_Hot_Water_Capacity


It's our Nigel again.
He has delusions of expertise and is liable to get the hump with
anyone who has the audacity to suggest that maybe some of his
proposals are not a very good idea.


> Bigger Tank

Yeah.

> Higher Thermostat Temperature

Scald risk, much higher standing energy losses. A lot more limescale
deposits itself at higher temperatures. The usual recommendation,
borne out of hands-on experience, is 60 degC storage.

> Drain Heat Exchanger
> --------------------
> A lot of heat goes down shower drains. Nearly the entire contents of the
> hot water tank in fact.

I am sceptical.
<<<

They work see gfx. Do a Google on this forum.

> They've never been sold commercially. I wonder why?

They are.

> Use CH Circuit Heat
> -------------------
> The Central Heating radiator circuit contains hot water in winter and
> tepid
> Water in summer. It is possible to harvest this heat and add it to the HW,
> thereby giving greater HW capacity.

No, it contains hot water in winter that's needed for heating. If it
contains tepid water in summer, there's something wrong with it.


> * With a heat bank or Thermal Store,

A thermal store? Why not store the therms in a bigger DHWS tank? I
must be missing something.
<<<

This is good to improve the flow to combi. The CH circuit is a thermal
store. He has been reading my posts (good boy :)). I have actually
implemented this. Works well.

>>>>
> The cold water supply goes through
> a heat exchanger on the CH circuit before going to the HW heat
> exchanger.

> * With a combi, the cold water supply to the combi goes through the CH
> exchanger, thus boosting the heat output for a while.

All the boiler water gets diverted to the DHWS heat exchanger. You
can't utilise the heat going to the CH circuit because when there's a
DHWS demand, there isn't any. The combi CH usually goes off while you
run the hot water.
<<<<<

With a combi using a plate heat X, flowswitch, a pump and a check valve or
two, when DHW is called the cold mains gores through a plate which pre-heats
from heat that is stored in the rads. Works well in summer too, and cools a
house slightly as the rads get cooler in summer.

Do a google on my name I explain how to do it. Cheap and easy to fill a bath
quickly. The rads go cold, but the boiler quickly re-hearty them when the
taps are off. Very effective. TRVs can restrict performance


Doctor Drivel

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Feb 7, 2008, 7:36:10 PM2/7/08
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"Doctor Drivel" <Min...@nospam.com> wrote in message
news:fog5u9$tj0$4...@aioe.org...

> This is good to improve the flow to combi. The CH circuit is a thermal
> store. He has been reading my posts (good boy :)). I have actually
> implemented this. Works well.

found it....

You could use the heat stored in radiators and use then radiators as a store
of heat. they would cool rapidly and when switched to CH re-heat rapidly
too. They will give 20-25C in summer and maybe even cool the house.

The heat in a full heating system can be used to pre-heat cold mains
pressure hot water. This can be done. I have seen this done using a plate
heat exchanger, pump, flowswitch and two check valves. The system should
not have thermostatic rad valves, or few of them. On a combi system:

- a by-pass pipe between the flow and return at the boiler
- on this pipe a re-heat plate heat exchanger is fitted
- The pump is fitted between the plate and the return by-pass pipe tee to
the return.
- A check valve between the pump and the plate
- A check valve on the boiler flow before the tee to the by-pass pipe.
- A flow switch on the cold mains water before the pre-heated plate heat
exchanger.

The check valve on the flow pipe ensure no flow back into the boiler,
although the internal 3-way valve should do this.
The check valve on the by-pass pipe ensures no short circuit in normal CH
operation.

The cold mains water runs through the pre-heat plate heat exchanger. This
pre-heated main water then runs into the combi as normal. When calling for
DHW the combi diverts to DHW only to heat the incoming cold water (but this
is pre-heated).
The flow of mains water is detected by the flow switch and switches on the
by-pass pump. This pumps water from the rads into the pre-heat plate heat
exchanger. This will raise the mains water substantially and the combi tops
up.

You can fill a bath up in a few minutes doing it this way. The rads cool
down a lot. This doesn't matter as when the system switches over to CH, the
boiler re-heats the rads ASAP with alarge combi boiler ouput, with loss in
room temp so small it is not noticeable to the occupants.

The combi flow rate in summer, when the CH is off is better than an average
flowrate combi as the water in the rads will be around 20 - 25C when the CH
is off. This stored 20C plus heat is used to pre-heat the cold mains water,
which is around 10-12C. Depending on the efficiency of the plate heat
exchanger and power of the boiler, the flow rate may be very good, even in
summer. Cooling the rads also helps to cool the house in summer too.

A simple and cheap way to vastly improve the output of a combi.

Andy Hall

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Feb 7, 2008, 8:07:43 PM2/7/08
to
On 2008-02-07 08:33:55 +0000, "Tim Downie"
<timdow...@obviousyahoo.co.uk> said:

Exactly. Once there are females, forget it.

Having said that, method 8 works as follows:

- Said females wash their hair at length in the shower.

- This causes a suitably chosen drain to reduce in flow as a result of
the collection of hair around the drain.

- Females turn down the shower valve to avoid the water running over
the edge of the shower tray.

- This increases water capacity.

The factor not taken into consideration thus far is the male grief factor.

Andy Hall

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Feb 7, 2008, 8:15:01 PM2/7/08
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On 2008-02-07 23:29:30 +0000, Onetap <one...@talk21.com> said:
>
>> Higher Thermostat Temperature
>
> Scald risk, much higher standing energy losses.

Irrelevant because they are tiny in the first place. If the loss
increases from 50W to 100W in the context of 5kW of energy use it is
not even a discussion point. Scald risk is ameliorated with a
thermostatic valve. Even the NHS can manage to provide a spec. for
this and they are totally incompetent.

> A lot more limescale
> deposits itself at higher temperatures.

Irrelevant with a water softener.


> The usual recommendation,
> borne out of hands-on experience, is 60 degC storage.

Thermal stores operate at around 80 degrees, so this is a non issue.


>
>> Drain Heat Exchanger
>> --------------------
>> A lot of heat goes down shower drains. Nearly the entire contents of the
>> hot water tank in fact.
>
> I am sceptical. You'd need a tube-in-shell heat exchanger and these
> are becoming unusual because of the cost of copper. A plate heat
> exchanger is impractical due to fouling and primary-side resistance.
> Plastic's thermal conductivity makes it implausible. The fouling
> factor would be huge and it would require frequent cleaning to remove
> the hair, soap scum, pubes, urine, etc.. You'd also have stagnant
> water on the secondary side when not in use, warmed to blood heat when
> it was and a risk of contamination from the drains to the mains. So,
> having constructed a legionella breeding incubator, you spray the
> water out of a shower. Sounds great.
>
> They've never been sold commercially. I wonder why?

Because they are pretty much pointless.

>
>> Move Thermostat Lower
>
> Similar to turning the thermostat up. Higher standing losses, scald
> risk, limescale accumulations.

Non issues.

Tim Downie

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Feb 8, 2008, 1:27:03 PM2/8/08
to

"Doctor Drivel" <Min...@nospam.com> wrote in message
news:fog5u7$tj0$2...@aioe.org...

Big difference between a bath water usage pattern and a shower though. At
least with a shower, you're drawing water (that can be usefully preheated)
at the same time as water is going down the drain.

With a bath though, it's fiill first, then empty. So, how are you going to
capture & store all this low grade heat you've recovered unless you have
system of pumps & separate heat storage tank? Seem hugely complicated for
any potential gains.

Tim
>


Onetap

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Feb 8, 2008, 3:17:09 PM2/8/08
to
On 8 Feb, 01:15, Andy Hall <an...@hall.nospam> wrote:
> > Scald risk, much higher standing energy losses.
>
> Irrelevant because they are tiny in the first place.   If the loss
> increases from 50W to 100W in the context of 5kW of energy use it is
> not even a discussion point.   Scald risk is ameliorated with a
> thermostatic valve.

From the cylinder. And from the boiler, pump, pipework etc., those
increased standing losses are how much?

> > A lot more limescale
> > deposits itself at higher temperatures.
>
> Irrelevant with a water softener.

Who mentioned a softener? Now you need a softener to increase your dhw
storage capacity?

> > The usual recommendation,
> > borne out of hands-on experience, is 60 degC storage.
>
> Thermal stores operate at around 80 degrees, so this is a non issue.

Er, yeah. They do. Bit they're not DHW stores; they make hot water
with an immersed internal pipe coil or an external plate heat
exchanger.
And, guess what? They scale up. Unless you have a softener, of course.


> >> Drain Heat Exchanger

> > They've never been sold commercially. I wonder why?
>
> Because they are pretty much pointless.

Yeah, it was a hypothetical question, see, coming after I'd explained
in detail why they were bolleaux.

> >> Move Thermostat Lower
>
> > Similar to turning the thermostat up. Higher standing losses, scald
> > risk, limescale accumulations.
>
> Non issues.

Same issues as turning up the storage temperature.

John Stumbles

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Feb 8, 2008, 6:10:13 PM2/8/08
to
On Fri, 08 Feb 2008 01:07:43 +0000, Andy Hall wrote:

> - Females turn down the shower valve to avoid the water running over
> the edge of the shower tray.

On what planet do females do that?!

--
John Stumbles

Women always generalise

Andy Hall

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Feb 8, 2008, 6:22:50 PM2/8/08
to
On 2008-02-08 20:17:09 +0000, Onetap <one...@talk21.com> said:

> On 8 Feb, 01:15, Andy Hall <an...@hall.nospam> wrote:
>>> Scald risk, much higher standing energy losses.
>>
>> Irrelevant because they are tiny in the first place.   If the loss
>> increases from 50W to 100W in the context of 5kW of energy use it is
>> not even a discussion point.   Scald risk is ameliorated with a
>> thermostatic valve.
>
> From the cylinder. And from the boiler, pump, pipework etc., those
> increased standing losses are how much?

Negligible because the boiler modulates down and switches of when there
is no demand.


>
>>> A lot more limescale
>>> deposits itself at higher temperatures.
>>
>> Irrelevant with a water softener.
>
> Who mentioned a softener? Now you need a softener to increase your dhw
> storage capacity?

No. It's simply a means to make the scaling argument irrelevant.


>
>>> The usual recommendation,
>>> borne out of hands-on experience, is 60 degC storage.
>>
>> Thermal stores operate at around 80 degrees, so this is a non issue.
>
> Er, yeah. They do. Bit they're not DHW stores; they make hot water
> with an immersed internal pipe coil or an external plate heat
> exchanger.
> And, guess what? They scale up. Unless you have a softener, of course.

So get a water softener. Good grief.

>
>
>>>> Drain Heat Exchanger
>
>>> They've never been sold commercially. I wonder why?
>>
>> Because they are pretty much pointless.
>
> Yeah, it was a hypothetical question, see, coming after I'd explained
> in detail why they were bolleaux.
>
>>>> Move Thermostat Lower
>>
>>> Similar to turning the thermostat up. Higher standing losses, scald
>>> risk, limescale accumulations.
>>
>> Non issues.
>
> Same issues as turning up the storage temperature.

So either do it or don't

If you want more hot water, it means more storage volume, higher
temperature or less temperature rise.

mass, specific heat, temperature rise.

First form physics when I went to school. Doctorate these days,
after the Big Mac degree has been completed.

Andy Hall

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Feb 8, 2008, 6:21:16 PM2/8/08
to
On 2008-02-08 20:17:09 +0000, Onetap <one...@talk21.com> said:

> On 8 Feb, 01:15, Andy Hall <an...@hall.nospam> wrote:
>>> Scald risk, much higher standing energy losses.
>>
>> Irrelevant because they are tiny in the first place.   If the loss
>> increases from 50W to 100W in the context of 5kW of energy use it is
>> not even a discussion point.   Scald risk is ameliorated with a
>> thermostatic valve.
>
> From the cylinder. And from the boiler, pump, pipework etc., those
> increased standing losses are how much?

Negligible because the boiler modulates down and switches of when there
is no demand.


>

>>> A lot more limescale
>>> deposits itself at higher temperatures.
>>
>> Irrelevant with a water softener.
>
> Who mentioned a softener? Now you need a softener to increase your dhw
> storage capacity?

No. It's simply a means to make the scaling argument irrelevant.


>

>>> The usual recommendation,
>>> borne out of hands-on experience, is 60 degC storage.
>>
>> Thermal stores operate at around 80 degrees, so this is a non issue.
>
> Er, yeah. They do. Bit they're not DHW stores; they make hot water
> with an immersed internal pipe coil or an external plate heat
> exchanger.
> And, guess what? They scale up. Unless you have a softener, of course.

So get a water softener. Good grief.

>
>

>>>> Drain Heat Exchanger
>
>>> They've never been sold commercially. I wonder why?
>>
>> Because they are pretty much pointless.
>
> Yeah, it was a hypothetical question, see, coming after I'd explained
> in detail why they were bolleaux.
>
>>>> Move Thermostat Lower
>>
>>> Similar to turning the thermostat up. Higher standing losses, scald
>>> risk, limescale accumulations.
>>
>> Non issues.
>
> Same issues as turning up the storage temperature.

So either do it or don't

Andy Hall

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Feb 8, 2008, 7:05:47 PM2/8/08
to
On 2008-02-08 23:10:13 +0000, John Stumbles <john.s...@ntlworld.com> said:

> On Fri, 08 Feb 2008 01:07:43 +0000, Andy Hall wrote:
>
>> - Females turn down the shower valve to avoid the water running over
>> the edge of the shower tray.
>
> On what planet do females do that?!

Good point.


I suppose that if they are hot, they would make the drain thing work better.


Appin

unread,
Feb 9, 2008, 12:54:19 PM2/9/08
to
The message <47acee5b@qaanaaq>
from Andy Hall <an...@hall.nospam> contains these words:

> Good point.

If they were genuinely that hot, they wouldn't be clogging the drain
with all the mess of hair and shaving soap they produce from shaving in
the shower in an effort to make themselves appear hot! :-)

meow...@care2.com

unread,
Feb 10, 2008, 5:12:44 AM2/10/08
to

or drain down.


> Extract from Primary circuit: In winter robbing the radiators will be
> counter productive (especially with a combi system).

If CH has priority, yes, if HW gets priority, no.


> 4) Down grade boost pump.

right


NT

NT

meow...@care2.com

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Feb 10, 2008, 5:17:13 AM2/10/08
to

>> Drain Heat Exchanger

>You'd need a tube-in-shell heat exchanger and these
>are becoming unusual because of the cost of copper.

I don't see the cost of the 2 copper pipes outweighing payback here.


>The fouling
>factor would be huge and it would require frequent cleaning to remove
>the hair, soap scum, pubes, urine, etc..

they're vertical, not horiz, which helps.

>You'd also have stagnant
>water on the secondary side when not in use, warmed to blood heat when
>it was

the cold feed is only warmed while its flowing. At other times it
cools down quickly, avoiding any bugfest.

> and a risk of contamination from the drains to the mains.

the mains water is under positive pressure.


> They've never been sold commercially. I wonder why?

They've long been used in industry, where there is a large amount of
heat to recover. They're now getting used in hotels where payback
potential is good. In some cases they can pay back in DIY use too. The
article links to a commercial seller for the hotel market.


NT

Onetap

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Feb 10, 2008, 7:51:15 AM2/10/08
to
On 10 Feb, 10:17, meow2...@care2.com wrote:
> Onetap wrote:

> I don't see the cost of the 2 copper pipes outweighing payback here.

You don't.

I studied thermodynamics, I do.

Heat transfer depends on surface area. A pipe-in-pipe heat exchanger
won't give you much heat treansfer area; you won't recover much heat.

Commercial heat exchangers were usually a tube-in-shell type ( a
'bundle' of copper tubes inside a pipe shell); these cost lots (cost
of copper, manual fabrication).

Recently plate heat exchangers have become much more common
(consisting of a 'stack' of plates).

In both types, note the large heat transfer area.

Heat transfer depends also on the temperature differential or LMTD.
The above commercially types work with large temperature differences
between primary and secondary, for DHWS something of the order of
80/60 and 10/60. What you propose has something like 30/10 and 10/20.

So, you've got sod-all surface area, bugger-all temperature
difference, giving you FA heat recovery and a huge maintenance
liability to boot.

I'm a little sceptical.

> >The fouling
> >factor would be huge and it would require frequent cleaning to remove
> >the hair, soap scum, pubes, urine, etc..
>
> they're vertical, not horiz, which helps.

Oh, good, that makes all the difference.

> >You'd also have stagnant
> >water on the secondary side when not in use, warmed to blood heat when
> >it was
>
> the cold feed is only warmed while its flowing. At other times it
> cools down quickly, avoiding any bugfest.

It would be insulated and you'd have stationary warm water, lying
there for a (potentially) long time between use.
Lest you think this is no problem, there is concern that the expansion
vessel on (UK) unvented water heaters may be a legionella incubator
and it was proposed to introduce flow-through types.

>> > and a risk of contamination from the drains to the mains.
>
> the mains water is under positive pressure.
>
> > They've never been sold commercially. I wonder why?
>
> They've long been used in industry, where there is a large amount of
> heat to recover. They're now getting used in hotels where payback
> potential is good. In some cases they can pay back in DIY use too. The
> article links to a commercial seller for the hotel market.

You could make it work commercially, where you would have a near
continuous waste water stream, but the controls & monitoring would be
costly.
The controls for a domestic sized one would be the same, unless you
sacrificed the safety.

Onetap

unread,
Feb 10, 2008, 10:49:13 AM2/10/08
to
On 10 Feb, 12:51, Onetap <one...@talk21.com> wrote:

>  Commercial heat exchangers were usually a tube-in-shell type ( a
> 'bundle' of copper tubes inside a pipe shell); these cost lots (cost
> of copper, manual fabrication).

http://en.wikipedia.org/wiki/Shell_and_tube_heat_exchanger

> Recently plate heat exchangers have become much more common
> (consisting of a 'stack' of plates).

http://en.wikipedia.org/wiki/Plate_heat_exchanger

>> In both types, note the large heat transfer area.

>    Heat transfer depends also on the temperature differential or LMTD.

http://en.wikipedia.org/wiki/LMTD

meow...@care2.com

unread,
Feb 11, 2008, 6:53:51 AM2/11/08
to
Onetap wrote:
> On 10 Feb, 10:17, meow2...@care2.com wrote:
> > Onetap wrote:

> > I don't see the cost of the 2 copper pipes outweighing payback here.
>
> You don't.
>
> I studied thermodynamics, I do.
>
> Heat transfer depends on surface area. A pipe-in-pipe heat exchanger
> won't give you much heat treansfer area; you won't recover much heat.
>
> Commercial heat exchangers were usually a tube-in-shell type ( a
> 'bundle' of copper tubes inside a pipe shell); these cost lots (cost
> of copper, manual fabrication).
>
> Recently plate heat exchangers have become much more common
> (consisting of a 'stack' of plates).
>
> In both types, note the large heat transfer area.
>
> Heat transfer depends also on the temperature differential or LMTD.
> The above commercially types work with large temperature differences
> between primary and secondary, for DHWS something of the order of
> 80/60 and 10/60. What you propose has something like 30/10 and 10/20.
>
> So, you've got sod-all surface area, bugger-all temperature
> difference, giving you FA heat recovery and a huge maintenance
> liability to boot.
>
> I'm a little sceptical.

understood. Are gfx's claims phoney then?


> > >You'd also have stagnant
> > >water on the secondary side when not in use, warmed to blood heat when
> > >it was
> >
> > the cold feed is only warmed while its flowing. At other times it
> > cools down quickly, avoiding any bugfest.
>
> It would be insulated

I don't see much likelihood of that, not for a domestic one

> and you'd have stationary warm water, lying
> there for a (potentially) long time between use.
> Lest you think this is no problem, there is concern that the expansion
> vessel on (UK) unvented water heaters may be a legionella incubator
> and it was proposed to introduce flow-through types.

Isnt that a dead leg though?


> >> > and a risk of contamination from the drains to the mains.
> >
> > the mains water is under positive pressure.

Like any product there are good and bad designs about. Double walled
exchangers are whats wanted, where there is no joint relied on for
water isolation. Ad example would be a central round pipe wrapped with
multiple parallel microbore pipes connected at each end to a manifold.


> > > They've never been sold commercially. I wonder why?
> >
> > They've long been used in industry, where there is a large amount of
> > heat to recover. They're now getting used in hotels where payback
> > potential is good. In some cases they can pay back in DIY use too. The
> > article links to a commercial seller for the hotel market.
>
> You could make it work commercially, where you would have a near
> continuous waste water stream, but the controls & monitoring would be
> costly.
> The controls for a domestic sized one would be the same, unless you
> sacrificed the safety.

Why would you need control or monitoring for domestic use?


NT

Doctor Drivel

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Feb 11, 2008, 10:41:34 PM2/11/08
to

"Onetap" <one...@talk21.com> wrote in message
news:85f6071d-90de-40f2...@s37g2000prg.googlegroups.com...

> On 10 Feb, 10:17, meow2...@care2.com wrote:
>> Onetap wrote:
>
>> I don't see the cost of the 2 copper pipes outweighing payback here.
>
> You don't.
>
> I studied thermodynamics, I do.
>
> Heat transfer depends on surface area. A pipe-in-pipe heat exchanger
> won't give you much heat treansfer area; you won't recover much heat.
>
> Commercial heat exchangers were usually a tube-in-shell type ( a
> 'bundle' of copper tubes inside a pipe shell); these cost lots (cost
> of copper, manual fabrication).

The Ethos combis has a tube-in-shell heat exchanger. 4 pipes inside one big
pipe. About the only combo that doesn't have a plate heat exchanger.

> Recently plate heat exchangers have become much more common
> (consisting of a 'stack' of plates).

These are compact and highly efficient.

You obviously didn't do what I said in previous posts. Look at:
http://gfxtechnology.com

It IS commercially viable. The gfx has been around for about 8 to 9 years.
The US government did tests and proved it economically viable.

Doctor Drivel

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Feb 11, 2008, 10:54:27 PM2/11/08
to
<meow...@care2.com> wrote in message
news:cd1c4632-ed0f-4974...@c23g2000hsa.googlegroups.com...

> Onetap wrote:
>> On 10 Feb, 10:17, meow2...@care2.com wrote:
>> > Onetap wrote:
>
>> > I don't see the cost of the 2 copper pipes outweighing payback here.
>>
>> You don't.
>>
>> I studied thermodynamics, I do.
>>
>> Heat transfer depends on surface area. A pipe-in-pipe heat exchanger
>> won't give you much heat treansfer area; you won't recover much heat.
>>
>> Commercial heat exchangers were usually a tube-in-shell type ( a
>> 'bundle' of copper tubes inside a pipe shell); these cost lots (cost
>> of copper, manual fabrication).
>>
>> Recently plate heat exchangers have become much more common
>> (consisting of a 'stack' of plates).
>>
>> In both types, note the large heat transfer area.
>>
>> Heat transfer depends also on the temperature differential or LMTD.
>> The above commercially types work with large temperature differences
>> between primary and secondary, for DHWS something of the order of
>> 80/60 and 10/60. What you propose has something like 30/10 and 10/20.
>>
>> So, you've got sod-all surface area, bugger-all temperature
>> difference, giving you FA heat recovery and a huge maintenance
>> liability to boot.
>>
>> I'm a little sceptical.
>
> understood. Are gfx's claims phoney then?

Look at these:

http://www.builditsolar.com/Projects/Conservation/GFXDOE-OIT-Sucess.pdf

http://oikos.com/products/mechanical/gfx/index.html

http://www.eere.energy.gov/consumer/your_home/water_heating/index.cfm/mytopic=13040

These units can be easily made by DIYers. The longer the copper drain tube
with a 15mm soft copper coil around it the better. The storage in the 15mm
soft copper is enough alone. Payback is between 2 - 5 years. That is very
good.

From US Dept of Energy: Economics

A recent field evaluation of the GFX conducted by Pennsylvania Power and
Light found the simple payback of a residential GFX system to range from 2
to 5 years. This was based on an installed GFX cost of $500 and electricity
savings ranging from 800 kWh/y to 2300 kWh/y depending on the average number
of daily showers in each home. The economics of the GFX improved with the
number of daily showers in the residence as expected. In general, buildings
that require large amounts of hot water for showers (e.g., homes of families
with several children, multifamily apartments, or barracks with showers on a
common drain line) would be ideal candidates for the GFX and would lead to
shorter paybacks.

In addition to operating cost reductions based on energy savings alone, the
GFX provides additional benefits. By recovering heat from drainwater and
simultaneously using this heat for preheating water to the water heater, the
GFX effectively shortens the time needed for the water heater to recover.
This is important if the existing water heater is undersized or if there are
more showers than usual taken back-to-back. Because heat is extracted from
drainwater by the GFX, the capacity of the water heating system is
increased. This means that it is possible to lower the thermostat setting on
the water heater without directly affecting the capacity of the water
heating system. These benefits, however, depend on hot water consumption
patterns and the fraction of overall hot water consumption that is amenable
to heat recovery by the GFX.

meow...@care2.com

unread,
Feb 16, 2008, 5:00:56 PM2/16/08
to
Onetap wrote:
> On 10 Feb, 10:17, meow2...@care2.com wrote:
> > Onetap wrote:

> > I don't see the cost of the 2 copper pipes outweighing payback here.
>
> You don't.
>
> I studied thermodynamics, I do.
>
> Heat transfer depends on surface area. A pipe-in-pipe heat exchanger
> won't give you much heat treansfer area; you won't recover much heat.
>
> Commercial heat exchangers were usually a tube-in-shell type ( a
> 'bundle' of copper tubes inside a pipe shell); these cost lots (cost
> of copper, manual fabrication).
>
> Recently plate heat exchangers have become much more common
> (consisting of a 'stack' of plates).
>
> In both types, note the large heat transfer area.
>
> Heat transfer depends also on the temperature differential or LMTD.
> The above commercially types work with large temperature differences
> between primary and secondary, for DHWS something of the order of
> 80/60 and 10/60. What you propose has something like 30/10 and 10/20.
>
> So, you've got sod-all surface area, bugger-all temperature
> difference, giving you FA heat recovery and a huge maintenance
> liability to boot.
>
> I'm a little sceptical.

OTOH you get film flow with the vertical pipes, which is several
times as effective at heat transfer as bulk flow.

Probably a good place to get unbiased figures is alt.solar.thermal.


> > >The fouling
> > >factor would be huge and it would require frequent cleaning to remove
> > >the hair, soap scum, pubes, urine, etc..
> >
> > they're vertical, not horiz, which helps.
>
> Oh, good, that makes all the difference.

not sure exactly how effective the ocasional dose of hot caustic
would be. It sure clears blockages well.

But these are really issues that, while of significance, dont greatly
change the increase capacity article. any other remaining issues
with the article?


NT

Onetap

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Feb 17, 2008, 5:38:47 AM2/17/08
to
On 12 Feb, 03:41, "Doctor Drivel" <Min...@nospam.com> wrote:

> > Heat transfer depends on surface area. A pipe-in-pipe heat exchanger
> > won't give you much heat treansfer area; you won't recover much heat.
>
> > Commercial heat exchangers were usually a tube-in-shell type ( a
> > 'bundle' of copper tubes inside a pipe shell); these cost lots (cost
> > of copper, manual fabrication).
>
> The Ethos combis has a tube-in-shell heat exchanger. 4 pipes inside one big
> pipe.  About the only combo that doesn't have a plate heat exchanger.

Yes, Drivel.
LTHW to DHWS heat exchanger, hence large LMTD.
We are speaking of Waste Water/DHWS heat exchangers, which have small
LMTD. Hence a larger surface area is required per unit of heat
transferrred.
You still need a secondary heat source to bring your warmed DHW up to
a useable temperature, and it's a breeding territory for legionella
and every other bug in it until you have done so.

IMHO, it's probably not worth the effort on a domestic scale.
You go ahead and build one if you feel inclined.

> You obviously didn't do what I said in previous posts. Look at:http://gfxtechnology.com

Drivel, I rarely read your posts and would never do what you
recommend.
This is because you are a clueless, moronic troll.

Doctor Drivel

unread,
Feb 17, 2008, 6:27:39 AM2/17/08
to

"Onetap" <one...@talk21.com> wrote in message
news:c8a3637f-8abc-4c77...@c33g2000hsd.googlegroups.com...

> You obviously didn't do what I said
> in previous posts. Look at: http://gfxtechnology.com

Drivel, I rarely read your posts
<<<

Mr Tap, well live in ignorance then...of which you amply display on a
regular basis. Sad but true.


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