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Need Heater Plumbing Advice
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Tom Kessler
Mar 18, 2013, 10:05:38 AM3/18/13
to
I'd like an expert opinion on the best plumbing and control scheme for the following solar hot water system.
1 - Two story home in a sub-tropical climate (20 N Lat) - never freezes, no glycol, etc.
2- Evacuated tube collector with 25 gallon tank on the roof.
3 - LP gas water heater on 1st floor.
4 - House is plumbed with hot water recirculation line to boiler from farthest bathroom.
Would like suggestions a completly automatic control and plumbing scheme between solar only, boiler assisted, and boiler only modes. I can retrofit the boiler to electronic pilot ignition.
Has anyone tried to implement this and optimize number of valves, controller, etc?
Or refer me to someone who has... thanks
1 - Two story home in a sub-tropical climate (20 N Lat) - never freezes, no glycol, etc.
2- Evacuated tube collector with 25 gallon tank on the roof.
3 - LP gas water heater on 1st floor.
4 - House is plumbed with hot water recirculation line to boiler from farthest bathroom.
Would like suggestions a completly automatic control and plumbing scheme between solar only, boiler assisted, and boiler only modes. I can retrofit the boiler to electronic pilot ignition.
Has anyone tried to implement this and optimize number of valves, controller, etc?
Or refer me to someone who has... thanks
Ecnerwal
Mar 18, 2013, 10:55:11 AM3/18/13
to
In article <b880442f-ead6-43de...@googlegroups.com>,
Many ways to approach this. Somebody did a sales job to get evacuated
tubes in that climate - flat plate will do more bang for the buck, but
what's bought is bought. My personal preference would be to put a PV
panel and circulator pump on the system to move hot water down off the
roof when the sun shines, and allow for more storage capacity by using
the LP water heater tank (unless it's tankless - you switch between
calling it a water heater and a boiler) as additional storage, or add a
large tank for storage. If your roof can stand the load, a big tank on
the roof allows things to be more passive, but that often is not an
option.
Some folks don't want to booger things up with electrics. But you
already have a pump. You can do it with line-powered pumps and sensors,
but the PV panel powered pump simplifies the controls - if the sun
shines, the pump runs, and the heater is heating. Cloud comes in, it all
slows down. Night falls, it stops.
Does the recirculator run all the time? If so, fix that. You can put it
on a switch, or even put it on a motion sensor so if someone moves
_near_ the bathroom(s) it starts recirculating for 15 minutes. Things
that run 24/7/365 when they are used a lot less than that can be
massively wasteful. Also, insulate all the pipes on that loop as if you
were in the arctic - they bleed heat from your hot water system into
your air conditioning load, so you pay at least twice for the heat
leakage.
Speaking of A/C, unless you are among the few that don't have it at that
latitude, add a "desuperheater" to your A/C unit to get more efficient
A/C and "free" hot water at the same time.
As for the "completely automatic control of modes" - the boiler/water
heater draws water from the solar storage. If it's not hot, or just not
hot enough, it kicks on; if it's hot enough, it does not. Cold water
supply feeds into the cold end of the solar storage and/or through the
collectors. Recirculation of the solar loop should feed the hottest
water (from the collectors) to the hot end of the LP water heater, and
the cold end of the LP water heater flows back to the hot end of the
dedicated solar storage, and the cold end of that goes out to the
collectors to be heated. Again, insulate the pipes in this loop well, or
you'll lose a lot of heat you could be storing.
You will probably also need a tempering valve, since there is
significant potential to have water stored that is MUCH hotter than you
want coming out of the faucet (scalding/burning.) That will take your
stored hot water and mix in enough cold water to limit the temperature
if it is too hot.
--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.
tubes in that climate - flat plate will do more bang for the buck, but
what's bought is bought. My personal preference would be to put a PV
panel and circulator pump on the system to move hot water down off the
roof when the sun shines, and allow for more storage capacity by using
the LP water heater tank (unless it's tankless - you switch between
calling it a water heater and a boiler) as additional storage, or add a
large tank for storage. If your roof can stand the load, a big tank on
the roof allows things to be more passive, but that often is not an
option.
Some folks don't want to booger things up with electrics. But you
already have a pump. You can do it with line-powered pumps and sensors,
but the PV panel powered pump simplifies the controls - if the sun
shines, the pump runs, and the heater is heating. Cloud comes in, it all
slows down. Night falls, it stops.
Does the recirculator run all the time? If so, fix that. You can put it
on a switch, or even put it on a motion sensor so if someone moves
_near_ the bathroom(s) it starts recirculating for 15 minutes. Things
that run 24/7/365 when they are used a lot less than that can be
massively wasteful. Also, insulate all the pipes on that loop as if you
were in the arctic - they bleed heat from your hot water system into
your air conditioning load, so you pay at least twice for the heat
leakage.
Speaking of A/C, unless you are among the few that don't have it at that
latitude, add a "desuperheater" to your A/C unit to get more efficient
A/C and "free" hot water at the same time.
As for the "completely automatic control of modes" - the boiler/water
heater draws water from the solar storage. If it's not hot, or just not
hot enough, it kicks on; if it's hot enough, it does not. Cold water
supply feeds into the cold end of the solar storage and/or through the
collectors. Recirculation of the solar loop should feed the hottest
water (from the collectors) to the hot end of the LP water heater, and
the cold end of the LP water heater flows back to the hot end of the
dedicated solar storage, and the cold end of that goes out to the
collectors to be heated. Again, insulate the pipes in this loop well, or
you'll lose a lot of heat you could be storing.
You will probably also need a tempering valve, since there is
significant potential to have water stored that is MUCH hotter than you
want coming out of the faucet (scalding/burning.) That will take your
stored hot water and mix in enough cold water to limit the temperature
if it is too hot.
--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.
Tom Kessler
Mar 18, 2013, 2:10:58 PM3/18/13
to
Dear Ecnerwal,
Thank you for the guidance I was looking for! I can visualize a plan now. A few additional comments:
- While I'm at 20 N Lat, (103 W) I'm also at 5000 ft. We still get chilly days where convection losses are a factor. I haven't bought the collector yet. Both types are available. How to make a more informed decision?
- recirc pump will have a thermostat. Have taco SS pump, not installed yet.
- LP heater is conventional with 132L tank (purchased that big just in case of -too many visitors and cloudy days) Its also possible to buy a tube w/o tank collector and leverage just the boiler tank.
- tempering valve ok.
- All hot water piping is well insulated.
- I left two additional insulated runs between boiler and roof , 3/4" and 1/2".
- Have no AC
- Water is pressurized hydroneumatic.
- Tempering valve understood.
Any additional thoughts?
thanks,
Tom
-
Thank you for the guidance I was looking for! I can visualize a plan now. A few additional comments:
- While I'm at 20 N Lat, (103 W) I'm also at 5000 ft. We still get chilly days where convection losses are a factor. I haven't bought the collector yet. Both types are available. How to make a more informed decision?
- recirc pump will have a thermostat. Have taco SS pump, not installed yet.
- LP heater is conventional with 132L tank (purchased that big just in case of -too many visitors and cloudy days) Its also possible to buy a tube w/o tank collector and leverage just the boiler tank.
- tempering valve ok.
- All hot water piping is well insulated.
- I left two additional insulated runs between boiler and roof , 3/4" and 1/2".
- Have no AC
- Water is pressurized hydroneumatic.
- Tempering valve understood.
Any additional thoughts?
thanks,
Tom
-
Bob F
Mar 18, 2013, 9:05:22 PM3/18/13
to
Tom Kessler wrote:
> Dear Ecnerwal,
>
> Thank you for the guidance I was looking for! I can visualize a plan
> now. A few additional comments:
>
> - While I'm at 20 N Lat, (103 W) I'm also at 5000 ft. We still get
> chilly days where convection losses are a factor. I haven't bought
> the collector yet. Both types are available. How to make a more
> informed decision?
>
> - recirc pump will have a thermostat. Have taco SS pump, not
> installed yet.
My recirc pump has a low voltage push button and a time deley relay to run it
> Dear Ecnerwal,
>
> Thank you for the guidance I was looking for! I can visualize a plan
> now. A few additional comments:
>
> - While I'm at 20 N Lat, (103 W) I'm also at 5000 ft. We still get
> chilly days where convection losses are a factor. I haven't bought
> the collector yet. Both types are available. How to make a more
> informed decision?
>
> - recirc pump will have a thermostat. Have taco SS pump, not
> installed yet.
for a couple minutes - plenty of time to have warm pipes to the room. Walk into
the bath and push the button. A minute or two later the hot water is there.
Ecnerwal
Mar 19, 2013, 6:59:28 PM3/19/13
to
In article <038e7c27-8c37-4661...@googlegroups.com>,
Basically, you look at the detailed rating information for the
temperature rise fitting your application, and then you have to factor
in the price. Before THAT you may need to see if anything you have
locally available is even a rated item, if not, you are back to
guesswork. A GLAZED flat plate will handle "chilly days" just fine,
IMHO. The UNGLAZED ones are severely limited (basically only good for
swimming pool heating.)
Evacuated tubes are "neat" but some of the Chinese ones are not that
good (as with anything, they can make it look like the things that do
well, but it may not perform as well if they only went for the look) and
for DHW applications in less-extreme climates, flat plate nearly always
wins on both BTUs per area (or kWh/m**2) and on $. Or Pesos ;-)
For instance, a Heliodyne Gobi HT rates at 4.01-4.05 kWh/m**2 (glazed
flat plate) on the "clear C" condition. The worst flat plate is 0.9.
The best tubular is 3.67 The worst tubular is 1.62.
You will need to do enough reading to understand what the ratings mean -
the main thing is the A B C D E class rating, having to do with the
temperature rise over ambient - C happens to be the class for "warm
climate domestic hot water." Good evacuated tubes thrash flat plates at
class E performance, but that has little application to typical domestic
hot water, and usually costs a LOT more for the collector. At 45 N I
need to consider at least class D performance - you probably don't, or
at least not much, in a climate that never freezes.
> - recirc pump will have a thermostat. Have taco SS pump, not installed yet.
> - LP heater is conventional with 132L tank (purchased that big just in case
> of -too many visitors and cloudy days) Its also possible to buy a tube w/o
> tank collector and leverage just the boiler tank.
I'd suggest trying it with just the 132 L, or getting an extra tank NOT
on the roof that you plumb in just ahead of the LP tank (unless you have
a nice sturdy flat concrete hurricane-proof roof that can become a floor
the next time you decide to build more walls and another roof. I've seen
those houses in parts of the tropics.) Depending on how willing you are
to rework it later, you can always add more storage capacity if you find
that it runs out too soon at a given size of storage. I assume you get a
bit more cloud cover than parts north of you with the sea nearby; the
good news is that both flat plates and evacuated tubes collect some heat
even on cloudy days - not that they can do miracles. If you get some sun
nearly everyday (even if not all day) you may not need a huge storage
capacity. We get long gray stretches, so much larger storage makes more
sense here.
You'll also need (should already have with the water heater) a
temperature/pressure relief valve, in case things get way too hot. You
may find that at some times of the year or day you want to be able to
cover (shade) part of the collector, if the T/P relief is blowing off
too regularly (when you get much more sun than you need for your hot
water use.) More storage can help with that problem as well. Make sure
that the drain from that valve is directed somewhere that will not cause
problems or burn anyone if or when it goes.
Tom Kessler <tka...@gmail.com> wrote:
> - While I'm at 20 N Lat, (103 W) I'm also at 5000 ft. We still get chilly
> days where convection losses are a factor. I haven't bought the collector
> yet. Both types are available. How to make a more informed decision?
http://www.solar-rating.org
> - While I'm at 20 N Lat, (103 W) I'm also at 5000 ft. We still get chilly
> days where convection losses are a factor. I haven't bought the collector
> yet. Both types are available. How to make a more informed decision?
Basically, you look at the detailed rating information for the
temperature rise fitting your application, and then you have to factor
in the price. Before THAT you may need to see if anything you have
locally available is even a rated item, if not, you are back to
guesswork. A GLAZED flat plate will handle "chilly days" just fine,
IMHO. The UNGLAZED ones are severely limited (basically only good for
swimming pool heating.)
Evacuated tubes are "neat" but some of the Chinese ones are not that
good (as with anything, they can make it look like the things that do
well, but it may not perform as well if they only went for the look) and
for DHW applications in less-extreme climates, flat plate nearly always
wins on both BTUs per area (or kWh/m**2) and on $. Or Pesos ;-)
For instance, a Heliodyne Gobi HT rates at 4.01-4.05 kWh/m**2 (glazed
flat plate) on the "clear C" condition. The worst flat plate is 0.9.
The best tubular is 3.67 The worst tubular is 1.62.
You will need to do enough reading to understand what the ratings mean -
the main thing is the A B C D E class rating, having to do with the
temperature rise over ambient - C happens to be the class for "warm
climate domestic hot water." Good evacuated tubes thrash flat plates at
class E performance, but that has little application to typical domestic
hot water, and usually costs a LOT more for the collector. At 45 N I
need to consider at least class D performance - you probably don't, or
at least not much, in a climate that never freezes.
> - recirc pump will have a thermostat. Have taco SS pump, not installed yet.
> - LP heater is conventional with 132L tank (purchased that big just in case
> of -too many visitors and cloudy days) Its also possible to buy a tube w/o
> tank collector and leverage just the boiler tank.
on the roof that you plumb in just ahead of the LP tank (unless you have
a nice sturdy flat concrete hurricane-proof roof that can become a floor
the next time you decide to build more walls and another roof. I've seen
those houses in parts of the tropics.) Depending on how willing you are
to rework it later, you can always add more storage capacity if you find
that it runs out too soon at a given size of storage. I assume you get a
bit more cloud cover than parts north of you with the sea nearby; the
good news is that both flat plates and evacuated tubes collect some heat
even on cloudy days - not that they can do miracles. If you get some sun
nearly everyday (even if not all day) you may not need a huge storage
capacity. We get long gray stretches, so much larger storage makes more
sense here.
You'll also need (should already have with the water heater) a
temperature/pressure relief valve, in case things get way too hot. You
may find that at some times of the year or day you want to be able to
cover (shade) part of the collector, if the T/P relief is blowing off
too regularly (when you get much more sun than you need for your hot
water use.) More storage can help with that problem as well. Make sure
that the drain from that valve is directed somewhere that will not cause
problems or burn anyone if or when it goes.
Tom Kessler
Mar 20, 2013, 6:39:08 AM3/20/13
to
On Tuesday, March 19, 2013 4:59:28 PM UTC-6, Ecnerwal wrote:
>
>
>
> > - While I'm at 20 N Lat, (103 W) I'm also at 5000 ft. We still get chilly
>
> > days where convection losses are a factor. I haven't bought the collector
>
Thanks very much! This has been very educational. I've two good options here for certified flat plates, Kioto and Modulo Solar. Not quite Heliodyne performance, but seems very respectable. It'll be interesting to quote and compare.
>
>
>
> > - While I'm at 20 N Lat, (103 W) I'm also at 5000 ft. We still get chilly
>
> > days where convection losses are a factor. I haven't bought the collector
>
If you're into solar electric, check out this company, Heart Tranverter in Costa Rica. http://www.transverter.com . I bought two, their installation is my next project!
Mho
Mar 20, 2013, 2:35:26 PM3/20/13
to
Do NOT attempt to use a "On-Demand" water heater. They do not work in this
application without extensive extra plumbing!
Instant hot water heaters (gas units) require a minimum BTU request to turn
on (smallest burner section available) . When your water is warm they will
not top up the temperature unless you draw a lot of volume!
------
"Tom Kessler" wrote in message
news:b880442f-ead6-43de...@googlegroups.com...
application without extensive extra plumbing!
Instant hot water heaters (gas units) require a minimum BTU request to turn
on (smallest burner section available) . When your water is warm they will
not top up the temperature unless you draw a lot of volume!
------
"Tom Kessler" wrote in message
news:b880442f-ead6-43de...@googlegroups.com...
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