Insulation properties of PVC conduit.
crispin...@gmail.com
I want to make a solar heater which will consist simply a series of
black pipes.
I was intending to use copper which I ten painted black however, I
wondered how well 20mm PVC electrical conduit would work. It's
available in 20 and 25mm (I would use 20) and is dirt cheap.
While I accept it won't be better than copper, would the PVC be too
much of an insulator to the contents (Either air or water)
The cheapness of it allows me to build a much bigger one for far less.
As the conduit is black, albeit shiny, I was going to give it a few
rubs with steelwool to dull it a bit.
Comments? Am I being penny wise, pound foolish?
TIA
Cheers,
Crispin
ga...@builditsolar.com
> Hi Folks, me again...
>
> I want to make a solar heater which will consist simply a series of
> black pipes.
> I was intending to use copper which I ten painted black however, I
> wondered how well 20mm PVC electrical conduit would work. It's
> available in 20 and 25mm (I would use 20) and is dirt cheap.
>
Hi,
If this is a glazed collector, I don't believe that the PVC will hold
up to the temperatures. It will be OK with water flowing through it,
but if the flow stops, the temperatures will be high enough to damage
the PVC.
It would probably work for an unglazed collector -- not sure about the
life.
Most water heating collectors use fins to transfer heat into the pipe
-- this increases the effective collection area.
A couple links you might find interesting:
http://www.builditsolar.com/Experimental/CPVCCollector/cpvccollector.htm
http://www.builditsolar.com/Experimental/PEXCollector/PEXCollector.htm
http://www.builditsolar.com/Projects/PoolHeating/SolarHotTub.htm
Gary
crispin...@gmail.com
Thanks Gary.
I think I might abandon the PVC option.
While it is cheaper, the copper pipe option is not exactly expensive.
Around £7 for a 3m length of 20mm pipe. I need 3-4 lengths. Having
said that, the PVC is £1.05 per length. ;)
I was not initially going to use any spreader plates. I was going to
suck off the hot air (it was to be a closed unit) and use that warm
air to warm a heat store (pebbles) Not that having or not having the
plates would affect the latter part.
I'm off to the shop this afternoon and will see what I can get in the
way of plates.
Thanks again..
David Williams
-> black pipes.
-> I was intending to use copper which I ten painted black however, I
-> wondered how well 20mm PVC electrical conduit would work. It's
-> available in 20 and 25mm (I would use 20) and is dirt cheap.
-> While I accept it won't be better than copper, would the PVC be too
-> much of an insulator to the contents (Either air or water)
-> The cheapness of it allows me to build a much bigger one for far less.
-> As the conduit is black, albeit shiny, I was going to give it a few
-> rubs with steelwool to dull it a bit.
-> Comments? Am I being penny wise, pound foolish?
You haven't told us many details, such as whether you want to heat a
swimming pool, where the water will always be quite cool, or if you
want to make really hot water.
Pool heaters often use plastic pipes. Sure, they're not as efficient as
copper ones would be, but they're so much cheaper that it's worthwhile
just to install more pipe. But plastic isn't good at high temperatures.
To make "hot" water, i.e. 60C or more, metal is preferable.
dow
crispin...@gmail.com
I am building a workshop and want to use this for heating. Basic idea
is to store the heat for use in the day as well as evening.
Storage "tanks" will be water or pebble.
What I am doing now is a small scale version for........my dog
kennel. :)
I have two options: Air heated stone or heated water store. Due to the
higher efficiency of water, The latter is probably the choice.
So I imagine the answer to your question is Cool(ish) I am not looking
at this as a replacement for my home immersion heater. I am looking to
raise the temperature of the kennel / workshop by a few degrees.
Hope that explains enough...
Jeff
You've got some choices to make!
It's much easier to store heat in water. It's cheaper to build an air
heater.
You may wish to use both, the air heater for heating during the day,
and the water heater for storing heat for the night.
Plastic pipe is only suitable for low temperature rise. That will
require a larger store and larger radiators to heat your space. I think
you will be better off biting the bullet now and building a better water
heater. Or looking into Thomason style trickle collectors.
Jeff
crispin...@gmail.com
I am going at this on a whim I agree. This is why I am doing the
kennel first. Must cheaper to make mistakes. :)
I have not come across the trickle down collectors. I assume this is
what you are talking about? http://www.jc-solarhomes.com/MTD/MTD_solar_heating.htm
How are they an advantage?
I really don't think I am going to go for the plastic option. While it
is cheaper, the copper option is not prohibitively expensive. I am now
trying to source some form of plate to use as a collector. I have a
few lengths of 20mm copper pipe lying around so will use that. I think
that they might be too thick but will see.
As for the storage, I was going to have a large, insulated, tub of
water. As I am building and designing the shed / workshop, I can
include this quite easily.
For both implementations, I am not looking to heat during the day but
store as much as I can during the day and heat at night. Suddenly the
size of the storage is scaring me. I don't want 1 cup of scalding
water but rather a large volume of tepid water. Any ideas on how I can
calculate this? I suppose there are too many variables in it such as
sun etc. Being in the UK, it'll be far less than my original South
Africa. Water in a garden hose could burn you!)
Cheers,
Crispin
David Williams
-> store as much as I can during the day and heat at night. Suddenly the
-> size of the storage is scaring me. I don't want 1 cup of scalding
-> water but rather a large volume of tepid water. Any ideas on how I can
-> calculate this? I suppose there are too many variables in it such as
-> sun etc. Being in the UK, it'll be far less than my original South
-> Africa. Water in a garden hose could burn you!)
-> Cheers,
-> Crispin
The heat capacity of water is 1 calorie (4.2 joules) per gram per
Celsius degree. So, suppose you want to hold enough heat to provide 5
kilowatts for a day, and suppose the water in your storage tank is
initially 30 deg. C above the minimum tolerable temperature, then:
4200 x V x 30 = 5000 x 24 x 3600
where V is the volume in litres.
Well, I don't have a calculator here, but 4200 x 30 must be about the
same as 5000 x 24. So V must be about 3600.
So that's 3.6 cubic metres. A big tank but not gigantic.
dow
Jeff
> Jeff,
>
> I am going at this on a whim I agree. This is why I am doing the
> kennel first. Must cheaper to make mistakes. :)
>
> I have not come across the trickle down collectors. I assume this is
> what you are talking about? http://www.jc-solarhomes.com/MTD/MTD_solar_heating.htm
I'm not working on one, so I really don't know. Essentially all they
really need is water trickling down a roof, typically corrugated metal
with some kind of glazing. It's collected in a gutter and recycled. Your
only major cost is the glazing. You could do the glazing with glass, or
using two cheap layers. An inner layer that is tolerant to water vapor
and an outer one that is UV resistant, and perhaps tougher.
>
> How are they an advantage?\
Potentially much lower cost.
> I really don't think I am going to go for the plastic option. While it
> is cheaper, the copper option is not prohibitively expensive. I am now
> trying to source some form of plate to use as a collector.
There's a number of people that sell the absorber plate ready to go. You
provide the box. Easy. I made mine using a sandwich of aluminum flashing
but it is extraordinarily time consuming!
I have a
> few lengths of 20mm copper pipe lying around so will use that. I think
> that they might be too thick but will see.
Collector design program:
http://sel.me.wisc.edu/codepro/new_codepro.html
>
> As for the storage, I was going to have a large, insulated, tub of
> water. As I am building and designing the shed / workshop, I can
> include this quite easily.
>
> For both implementations, I am not looking to heat during the day but
> store as much as I can during the day and heat at night. Suddenly the
> size of the storage is scaring me. I don't want 1 cup of scalding
> water but rather a large volume of tepid water. Any ideas on how I can
> calculate this?
Well, the heat in BTU's stored is easy to calculate. One pound of water
raised one degree F is one BTU. Similar equations for metric.
The cheapest way to heat a home is not to lose heat. Tighten and
insulate is the most cost effective plan.
There's a thread in this group titled "Tank Sizing", you may want to
read that.
I suppose there are too many variables in it such as
> sun etc. Being in the UK, it'll be far less than my original South
> Africa. Water in a garden hose could burn you!)
Well, that can be a problem. I know there are some parts of the UK
where it's just too overcast.
Google yields this:
http://cms.ises.org/uploads2/SSF/pictures/materials/307/solarrad.PDF
Jeff
>
> Cheers,
> Crispin
crispin...@gmail.com
> crispin.proc...@gmail.com wrote:
> > Jeff,
>
> > I am going at this on a whim I agree. This is why I am doing the
> > kennel first. Must cheaper to make mistakes. :)
>
> > I have not come across the trickle down collectors. I assume this is
David / Jeff,
Thanks for the answers. 3.6 cubic meter tank is large. Larger than I
thought I would need.
Thanks also for the programme - I've downloaded and installed it. I'll
have a play around with it.
Due to the size of the storage tank required, I had another thought.
(We talking workshop here)
If I already plan on a concrete floor, why not make the base thicker
(200mm). As the rough size of the workshop will be 6 X 9 with a base
of 200mm, that gives me roughly 10.8 cubic meters. Making this thicker
has a huge increase.
As, from what I have read, concrete is roughly 4 times less efficient
at storing heat than water, this will be made up in bulk. There would
be a slight loss due to the piping in the concrete for heat transfer.
A major drawback would be the fact that I cannot control the
dissipation of the heat. Having such a large surface area I am sure it
would dump it rather quickly. (There is of course insulation on the
sides and underneath it.)
Maybe I'll just got get a 1300W heater from my local electrical
store :) Naa, this is more fun.
Cheers,
Crispin
Jeff
Go run your own numbers. I think you can probably get by with a tank a
third the size for 5kWHr.
How much collector area are you planning on?
Jeff
crispin...@gmail.com
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -
Jeff,
I'm confused by something. (Probably the most fundamental thing here)
When you say 5KWh, how would you compare that to a small heater?
I have a heater which is 1.1KW. Is that then, if used over an hour,
5.5KWh?
Your measurement is a rate. Or am I missing something? (Hangs head
embarrassed)
Collector:
Initially it was a series of 15mm copper pipes spaced about 30mm
apart. Height is 500mm and length 1.8m. There would be two of them.
However, after advice (from here) I will change it to use plates (from
underfloor heating) which will space the pipes further apart but
obviously have a much larger surface area.
Today was a "hot" day. Not a cloud in the sky and probably around 25c
(Yes, that is hot). The water (still) in my test collector, which is
not in a protective box and cooled by the breeze, was very hot. A
tepid cup of tea it would have made. I lost my temp probe so could not
get the exact temperature...
Cheers,
Crispin
David Williams
-> > thought I would need.
-> Go run your own numbers. I think you can probably get by with a tank a
-> third the size for 5kWHr.
Or smaller. As far as I recall, I did the calculation for 5 kW for a
*day*, i.e. 120 kWh.
A lot depends on how much you can tolerate the water in the tank
cooling, i.e. the difference between its maximum and minimum
temperatures. I guessed 30 deg. C, but that's really quite a lot. If
the minimum temperature is 40 C, which is just lukewarm, then the
maximum would have to be 70 C, which is scalding hot. If you want the
range to be smaller, the tank has to be bigger.
For example, to produce 5 kWh with a temperature drop of only 10 deg.
C, the equation would be:
5 x 3.6e6 = 4700 x V x 10
which makes V equal 383 litres, or 0.383 cubic metres. That's only
about a tenth of the size of the tank I calculated. But would 5 kWh be
adequate? I can't see it being sufficient to keep a house warm through
a few winter nights and cloudy days in England?! I used to live there,
and I can't imagine that being enough.
dow
Jeff
A heater that uses 1 kW, will use 5 kWHr in 5 hours. Hence, kilowatt hours!
I didn't come up with that number, I don't know where it came from/
> Your measurement is a rate.
No, I said: 5kWHr
Or am I missing something? (Hangs head
> embarrassed)
>
> Collector:
> Initially it was a series of 15mm copper pipes spaced about 30mm
> apart. Height is 500mm and length 1.8m. There would be two of them.
So, about .9 m^2 each. or 1.8 m^2
Say you had a sunny spot with 5kWhr/m^2 per day of solar insolation.
That would give you about 4.5 kWhr (at 50% efficiency) per day to store.
Not a huge amount of heat. About one trash can of water at 20C
temperature rise. About one 1500 W heater running full blast for 3 hours.
I don't really think in metric, so you'll have to run your own numbers.
Jeff
David Williams
-> When you say 5KWh, how would you compare that to a small heater?
-> I have a heater which is 1.1KW. Is that then, if used over an hour,
-> 5.5KWh?
Power x time = energy. Watts, or kilowatts, measure power. Hours,
seconds, etc., measure time. Watts x seconds equal joules, a joule
being a unit of energy. Kilowatts x hours equal kilowatt-hours, which
is another unit of energy. 3.6 million joules equal 1 kilowatt-hour.
So if you ran your 1.1 kW heater for 1 hour, it would use 1.1 kWh. If
you ran it for 5 hours, it would use 5.5 kWh.
Get it?
dow
crispin...@gmail.com
My reason for stating / asking that KWh is a rate and not a quantity
is because of the time component.
Initially it did not make sense to say that "Here, in this bucket I
have 5KWh" But after I posted the last message, it was clear that my
mind had gone blank. Battery capacity is stated in AH. Makes sense
that you could use the same for heat / energy. I'm rambling.... :)
It all makes perfect sense. (Roger Waters)
Cheers,
Crispin
David Williams
-> is because of the time component.
-> Initially it did not make sense to say that "Here, in this bucket I
-> have 5KWh" But after I posted the last message, it was clear that my
-> mind had gone blank. Battery capacity is stated in AH. Makes sense
-> that you could use the same for heat / energy. I'm rambling.... :)
-> It all makes perfect sense. (Roger Waters)
-> Cheers,
-> Crispin
Everything ties together. A newton is the force that will give a mass
of 1 kilogram an acceleration of 1 metre per second squared. If a force
of 1 newton pushes something a distance of 1 metre, it expends 1 joule
of energy. If 1 joule is expended in 1 second, the power (rate of use
of energy) is 1 watt.
In electricity, 1 coulomb is a unit of electric charge. A rate of flow
of 1 coulomb per second is 1 ampere (amp). A volt is a unit of electric
force. If 1 volt causes 1 amp to flow, the power it dissipates is 1
watt - the same watt as in the mechanical case.
Hours mess things up a bit, because of the factors of 60. They are not
preferred units, but a lot of people use them out of habit. So a
kilowatt-hour (kWh) is 3.6 million joules.
Units that are named after people, e.g. watt, newton, joule, ampere,
are spelled with lowercase initials when they are written in full, but
when they are abbreviated to initials, they are in uppercase. Other
units (as far as I know) are always in lowercase. So a kilowatt-hour is
abbreviated to kWh.
Don't they teach this stuff in schools?
dow
Solar Flare
can they specify a range.
"kilowatthours"
"David Williams" <david.w...@bayman.org> wrote in message
news:1210260647.9...@bayman.org...
David Williams
-> can they specify a range.
Yes. So? Has anyone suggested otherwise?
-> "kilowatthours"
Or maybe you're mistaking the hyphen I used for a subtraction sign,
which it isn't.
-> > kilowatt-hour (kWh) is 3.6 million joules.
A period might be better. Omitting a separator altogether
-> "kilowatthours"
is definitely unconventional.
dow
Solar Flare
"David Williams" <david.w...@bayman.org> wrote in message
news:1210284245.9...@bayman.org...
J. Clarke
> You need to get out more often.
He's not the one picking at minutiae of nomenclature. Or are you
really not familiar with the well known composite unit of energy
"kilowatt-hours"?
--
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)
RF
> -> My reason for stating / asking that KWh is a rate and not a quantity
> -> is because of the time component.
> -> Initially it did not make sense to say that "Here, in this bucket I
> -> have 5KWh" But after I posted the last message, it was clear that my
> -> mind had gone blank. Battery capacity is stated in AH. Makes sense
> -> that you could use the same for heat / energy. I'm rambling.... :)
>
> -> It all makes perfect sense. (Roger Waters)
>
> -> Cheers,
> -> Crispin
>
> Everything ties together. A newton is the force that will give a mass
> of 1 kilogram an acceleration of 1 metre per second squared. If a force
> of 1 newton pushes something a distance of 1 metre, it expends 1 joule
>
> Don't they teach this stuff in schools?
>
> dow
Only in Ph.D. courses ;-)
J. Clarke
Well, they start teaching in Physics for Jocks, by the time a student
is in grad school it's starting to actually sink in.