2 Questions on Solar water heat, pipe & Tankless

SystemSystem Posts: 2,511 admin
Good day

Looking to build a small hot water collector/heater. Can I use CPVC tubing 3/4 inch for my internal piping or do I have to use copper?

Question 2 what would be the minimum size of a Propane tank to supply a tankless hot water heater. I can only handle small tanks because of remote area & no delivery service.

Regards

Ed

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,038 admin
    Re: 2 Questions on Solar water heat, pipe & Tankless

    You can read about CPVC piping here:

    http://www.builderswebsource.com/techbriefs/cpvccopper.htm

    You probably should check your local building code to make sure that it is allowed. Also, you should have a tempering valve (mixes cold water with water over 120+ degrees that frequently can be produced by solar collectors) to prevent burns and protect the plastic piping. Other than not using it to plumb your solar collector, it seems that CPVC is legal and safe to use (although there may be issues with exposure to vinyl with plastic piping--but there can also be issues with exposure to copper and acidic water too). Other than using PVC for sprinklers, I don't have any experience with plastic piping (Make sure that CPVC is not exposed to sun--may become brittle over time if like sprinkler piping).

    Watch also the type of tankless hot water heater you get--many do not account for the inlet water temperature and do not make good boosters for solar hot water systems. For example, here is a a Bosch brand designed for Solar/Wood Stove hot water backup (have not used these or the vendor--link supplied for information purposes only):

    http://www.tanklesswater.com/product.asp?product=125BS-LP

    Where my wife's family is from, they used, what looked to be, 20-25 kG propane tanks (about 40-50 lb) for cooking/tankless hot water heater without any problems.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: 2 Questions on Solar water heat, pipe & Tankless
    EDh wrote:
    Looking to build a small hot water collector/heater. Can I use CPVC tubing 3/4 inch for my internal piping or do I have to use copper? Ed


    Do you mean can you use CPVC to build the collector itself?
    If so, my answer would be no, because the CPVC, compared to copper pipe, would be like copper pipe with a half inch of insulation on it. This means that it would take forever for the suns heat to finally make it's way through the CPVC pipe, to warm the water. As to using CPVC to plumb your collector to your house, I've done that for some time now with no problems. Be aware though that when using a CPVC adapter to connect to a copper adapter, if hot water is involved, only use a male copper adapter and a female CPVC adapter, never the other way around. Reason being, the coefficient of expansion is different between the two materials and the female CPVC adapter has a built in rubber seal/washer to allow for expansion without leaking. Where I live, many people have very hard water that ruins copper pipe, but has no affect on CPVC, so it's used a lot to plumb houses. Great to work with, easy to use, no problems that I've heard of. Would I use it? I DO use it.
    Wayne
  • System2System2 Posts: 6,290 admin
    Re: 2 Questions on Solar water heat, pipe & Tankless

    Hello

    Sorry about posting in the wrong segment.

    Thanks for the replies, good catch on the insulation of CPVC vs copper. Seems like our Home D here stocks a gazillion feet of CPVC & Pvc for cold & about 42 feet of copper.

    I think I will wait till I get North & use the copper. Thanks for the link on the Tankless. I will email the supplier & make sure my 40's or 100 pounder will work & what the consumption rate may be.

    Thanks again for the input.

    Regards

    Edh
  • System2System2 Posts: 6,290 admin
    Re: 2 Questions on Solar water heat, pipe & Tankless

    CPVC is good for both hot and cold.
  • BB.BB. Super Moderators, Administrators Posts: 31,038 admin
    Re: 2 Questions on Solar water heat, pipe & Tankless

    EDh,

    I thought, that when you said "internal piping" you were probably talking about inside of the house. Using xPVC or any non-metallic piping for a solar collector would be bad news on several fronts (as Wayne typed)... It would not pass heat very well, and if used with a covered (glass box) collector--the hot weather and no flow would probably cook your pipe and cause them to fail...

    I have seen a home made collector that used coils of black pipe set flat on a roof (basically spriles of piping) used as, apparently, a solar pre-heater for domestic hot water. I would guess that if you wanted warm water without burning fuel (quick shower and washing of plates--as much hot water as stored in the coils of plastic pipe) it would probably work OK.

    Building a collector with pump and storage tanks would require a better system built from metal (copper would be best for the price) and a covered collector (if you want hot water in a cold(er) climate). Open collectors work OK up to a few degrees over air temperature. To get warmer than that, a covered/insulated (bottom/sides) is the way to go.

    When you talk with your supplier, it would probably help to know how much gas you will need (100,000 BTU/hr for 5 minutes or 1+ hour)... Other than the cost of gas, the only other issue I have seen is tanks freeze water on the outside when used for long periods of time (like melting Tar for a hot roof and running the burner for 8+ hours per day).

    Installing the tank where it can get warm(er) air to keep the pressure and temperature up would be helpful. I can't imagine any real issues with a 100lb tank--and even the 40 lb should be OK for intermittent use unless you get really cold weather (well below freezing) for longer periods of time. The ~40-50lb'ers used in Taiwan had nothing special done with them (of course, it does not usually get too cold there either).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: 2 Questions on Solar water heat, pipe & Tankless

    Hi Bill

    Sorry about the confusion re the pipe. I have 2 different worlds I seem to operate in in regards to piping. Here in Florida the PVC is used for cold 1/2 or 3/4 etc. & usually costs about $1.80 for 10 feet. The CPVC which is used for the Hot water supply with its own special glue costs about $3.00 for 10 feet. However the diameter of cpvc is so much smaller than the pvc. The 3/4" copper comes in at $19.00 for a 10 foot length. So my internal radiator for the collector was either going to be cheap or expensive. The collector will be used at our cabin which is located up by the Upper Peninsula in Michigan.

    We use the cabin June to September so although it's certainly cold for me in September, it doesn't freeze up. We are usually taking everything apart for storage by Sept 15. In regards to the Propane tank size we use a 10 gal hot water propane tank we brought back from Mexico and as per my luck it may need parts at some point, & I don't want to go to Mexico to get them so I figure maybe the tankless would be the way to go. Our 100# lasts about 4 years with our consumption. We consume 2 showers for the day & some dishes. Maybe an RV water heater could do the job.

    I still like the fun of living off the grid in the wilderness & think the solar heater would be a good project. Not sure what the payback would be but it would be a project. I have also been toying with an electric hot water heater using one of those 12 volt heater elements. I usually produce more electric than I use & between the hot water collector & the excess electricity I maybe able to get away from propane except for our stove.

    Regards

    Ed
  • BB.BB. Super Moderators, Administrators Posts: 31,038 admin
    Re: 2 Questions on Solar water heat, pipe & Tankless

    Using solar PV for electric hot water is probably not the way to go if you have any other uses for the electricity (fridge, fans, lighting, electronics, perhapsmore batteries for less generator use, etc.). Solar hot water collectors run, roughly, about $0.50 a watt vs $5.00 a watt for solar PV panels... Plus you would only need about 1/4 the square footage to collect the equivalent kW/BTU's of heat (solar PV is 12-18% efficient, solar hot water can be ~80% efficient).

    The RV hot water heater is probably the way to go--you could kill the pilot except when you actually need the hot water (or do they have pilot-less RV units now?). It is cheaper and requires less maintenance and winterization...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: 2 Questions on Solar water heat, pipe & Tankless

    i am also making a collector on my roof. my thought is to use spirals of higher pressure black irrigation tubing /pipe,i live in hawaii so freezing is not an issue.
    will the tubing hold 60 psi plus the high temp. ( 140 + ) . copper is very expensive here so the tubing is just a option i would like to explore. i have had a hard time getting temp specs on high quality tubing, also tubing comes in 5/8'' and i was hoping for 3/4'' tubing to match the house supply. our sun would destroy pvc pipe as it gets to 140 + degrees on the solar panels already installed. i can cover the inside top glass with shade cloth that absorbs the direct rays saving uv on what piping i use and still have high interior temps. sounds cheap but people use tubing here for irrigatioh with tubing exposed on the ground and it gets hot.
    jam
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: 2 Questions on Solar water heat, pipe & Tankless

    We use a Paloma ph6 water heater in almost exactly the same situation.
    The ph6 has a standing pilot that we can kill when we don't need (hot)water.
    If you do the math with the input rating from the heater ~40kbtu and the btu in a gallon/litre/pound of l/p gas you can figure it out. In simple terms we use 100# of l/p in 4-6 weeks. This includes the range and oven, (all with pilots) l/p fridge and hot water for dishes, laundry and showers.

    As to the use of copper over plastic. I second all the previous points. Even with the price of copper, a small collector will only need ~100' of pipe. I built mine with 1/2" copper with 180 degree elbows, sitting on a piece of scrap sheet steel, covered with a discarded tempered patio door glass panel. Mine simply thermosiphons into the pre-heat tank, slow but effective. A pump and hydro-stats would be better, but if it works,,,K.I.S.S.

    Also, as stated before, l/p tanks will sweat when they release their gas. If it is cold enough that condensation will freeze if the gas is coming out fast enough. (Not that it will hurt anything)

    Icarus
  • mike95490mike95490 Solar Expert Posts: 9,011 ✭✭✭✭✭
    Re: 2 Questions on Solar water heat, pipe & Tankless
    icarus wrote: »
    Also, as stated before, l/p tanks will sweat when they release their gas. If it is cold enough that condensation will freeze if the gas is coming out fast enough. (Not that it will hurt anything)
    Icarus

    In really cold weather, the vapor pressure of propane goes down, and you could have problems with the regulator (flat pancake looking thing at the tank valve) freezing stuck in a position. Usually the local propane dealer has installed items that work fine in local climates. This does not hold true if you buy stuff in the south, and truck it 3,000 miles north.
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  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: 2 Questions on Solar water heat, pipe & Tankless

    Just one more note,,,at minus 40f (c) the gas won't vaporize at all! You can open a tank and it will just sit there! Not a problem for most people, but for those of us here where it is cold it can be.

    Icarus
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