Solar Water Heater collector/system question

djdenali
djdenali Registered Users Posts: 11
Hope this is an appropriate forum for such questions...I am reading about a solar water heating set-up.

1) Am I correct that I need a solar collector AND a solar system to deliver the water? Can it work on a gravity feed system if the collector is above the house, about 100 vertical feet, 200 horizontal?

2) Are there any low-amperage (i.e.15 or so) on demand heaters? I read 200 amps are necessary.

3) The system would be for one, low-maintanence person. A batch collector seems like the most simple. However, I did read these are for climates that don't freeze. While I reside in coastal (i.e. Mediterrannean climate) California, it might get to the high 20's/low 30's a couple nights a year. Day time temps would not stay so low. Would this be an issue?

4) If the freezing is an issue, would a flat-plate collector be a good choice? Any other suggestions?

5) Regardless of which collector, excepting the batch, I would still need a storage tank AND a method/pump to deliver, correct? The panels are about 100 feet vertically above the house. If the tank goes there as well, would this be enough for a gravity feed set-up? It's a small set-up, 2 panels. Are there pumps that would work with such a system? How much upgrade would be necessary?

6) Any suggestions? Do you have any questions which I can answer or need to consider?


Thanks so much!
dj

Comments

  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Solar Water Heater collector/system question

    I have an open loop system which is not a drain down and get a couple nights a year below freezing. It has a small 120v pump and a 80 gallon electric hot water heater as a pre heat tank for my gas water heater. For about 11 months out of the year I have a tank of 140F water and my gas heater draws from it an it never Comes on, in fact we turn down the gas heater to just above a warm setting. On those nights when the temps are very low the controller occasional comes on and circulates water from the tank to the flat plate collector to prevent freezing of the system. Even the one month that doesn't complete meet our needs the tank temp still can reach 120-125F Midday and we use just a few therms of nat gas.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Solar Water Heater collector/system question

    here is a link to a Canadian company that sell DHW systems etc. you should be able to find some reasonable info towards your questions
    http://www.wsetech.com/
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Lee Dodge
    Lee Dodge Solar Expert Posts: 112 ✭✭
    Re: Solar Water Heater collector/system question

    I am doubtful that a collector located 100 vertical feet and 200 horizontal feet from the house will have much thermal energy left when it reaches the house. My collector is located almost directly above the solar hot water storage tank, with a total insulated pipe length of about 15 feet for both pipes.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar Water Heater collector/system question

    This is a neat system that has a remote solar thermal + storage tank plumbed to the home... Shows a lot of the details involved.

    http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Solar Water Heater collector/system question
    Lee Dodge wrote: »
    I am doubtful that a collector located 100 vertical feet and 200 horizontal feet from the house will have much thermal energy left when it reaches the house. My collector is located almost directly above the solar hot water storage tank, with a total insulated pipe length of about 15 feet for both pipes.

    Lee has a good point, mine is abou 25 ft directly above my tank as well.
  • Organic Farmer
    Organic Farmer Solar Expert Posts: 128 ✭✭
    Re: Solar Water Heater collector/system question
    djdenali wrote: »
    Hope this is an appropriate forum for such questions...I am reading about a solar water heating set-up.

    1) Am I correct that I need a solar collector AND a solar system to deliver the water? Can it work on a gravity feed system if the collector is above the house, about 100 vertical feet, 200 horizontal?

    You might be able to 'gravity-feed' water from a stream, down into the solar collector, and from there down into your home. But How would be re-circulate the water back up-hill again?

    Gravity-feed only works down-hill. :)
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Solar Water Heater collector/system question
    You might be able to 'gravity-feed' water from a stream, down into the solar collector, and from there down into your home. But How would be re-circulate the water back up-hill again?

    Gravity-feed only works down-hill. :)

    And convection only works well with high temperature differentials and maybe well insulated pipes.
    SMA SB 3000, old BP panels.
  • LucMan
    LucMan Solar Expert Posts: 223 ✭✭✭
    Re: Solar Water Heater collector/system question

    100' vertical and 200' horizontal= 600' of total pipe.
    That's a long piping run! I will questimate you will need approximately a 1/2- 3/4 HP pump at minimum 3 gpm through the 2 collectors.
    I would suggest that you find a closer location for your panels keeping your 1 way piping run < 50'
  • naptown
    naptown Registered Users Posts: 1
    Re: Solar Water Heater collector/system question
    LucMan wrote: »
    100' vertical and 200' horizontal= 600' of total pipe.
    That's a long piping run! I will questimate you will need approximately a 1/2- 3/4 HP pump at minimum 3 gpm through the 2 collectors.
    I would suggest that you find a closer location for your panels keeping your 1 way piping run < 50'

    New guy HERE some of you may know me from elsewhere. Saw this and had to chime in.
    In a closed loop system the vertical would be negated and only the pressure drop from the piping and fittings would be calculated. Now an open loop or drain back system is a differdnt story and would require a large pump.
    Still this is a long way from the house to the collectors
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar Water Heater collector/system question

    One of the problems with long supply loops is the liquid in the loop is a significant portion of the total thermal mass of the system...

    Normally one uses fairly large diameter piping (and a series of 45 degree/soft bends) to reduce restrictions and pumping losses.

    In this case, I wounder if using PEX (insulated and buried in a trench--has to withstand the heat and oxygen if open loop) or some other smaller diameter smooth flowing piping system and a higher pressure pump would be better... Otherwise, you are just heating the water in the loop and not doing much heating of the building/supply water at the end.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Skippy
    Skippy Solar Expert Posts: 310 ✭✭
    Re: Solar Water Heater collector/system question

    I still don't know how to "multi" quote, so here it is in one big go . . . hope it helps. . .

    Just my opinion . . . :p:D

    djdenali wrote: »
    Hope this is an appropriate forum for such questions...I am reading about a solar water heating set-up.

    1) Am I correct that I need a solar collector AND a solar system to deliver the water? Can it work on a gravity feed system if the collector is above the house, about 100 vertical feet, 200 horizontal?

    1. You can have a solar water heater without solar electric panels . . . as long as you can plug in an a/c pump to move the water around. . . A gravity feed system will work above the house, but as a general rule, try to keep the collectors as close to the "usage" as possible, the further you go, the more problems you run into - such as needing bigger pipes and bigger pumps - as well as major heat losses .

    2) Are there any low-amperage (i.e.15 or so) on demand heaters? I read 200 amps are necessary.

    2. You can get really small under sink - on demand water heaters - for just a small sink . . The smallest water heater that I was able to find (that could run my shower) was the tempra 12 by stieble eltron - this is the one I have at home right now, and I bought it as a back up for my solar water heater . . . works good for one person . . . your not going to get blasted out of the shower by any means, but it does the job.... in the middle of winter, with water coming in at around 65 degrees, I can have a nice hot shower - something like 104 degrees or so . . .

    Thermostatically Controlled? Yes, temperature control with full power modulation based on flow rate and incoming water temperature.
    KW 12 KW @ 240v / 9 KW @ 208v
    Voltage: 208 - 240 volts / single phase / 50 - 60 Hz
    Max. Amps: 50 AMPS @ 240v / 44 AMPS @ 208v
    Breaker Required:* 60 AMP breaker (depends on local codes)
    Wiring:* Minimum #6 AWG Copper (depends on local codes)
    Dimensions: 16.6 x 14.5 x 4.6" (42.0 x 36.8 x 11.7 cm)
    Weight: 13.2 lbs (6.1 KG)
    Pipe Fittings: 3/4" NPT
    Energy Efficiency: 99%+
    Activation Flow Rate: 0.37 GPM / 1.4 LPM


    3) The system would be for one, low-maintanence person. A batch collector seems like the most simple. However, I did read these are for climates that don't freeze. While I reside in coastal (i.e. Mediterrannean climate) California, it might get to the high 20's/low 30's a couple nights a year. Day time temps would not stay so low. Would this be an issue?

    4) If the freezing is an issue, would a flat-plate collector be a good choice? Any other suggestions?

    3 and 4. If freezing is an issue, and all you had was a flat plate collector, then a drain back system would work . . you would have to be darn sure that all the pipes are draining back completely, so excess water does not freeze and split the pipes. . .

    5) Regardless of which collector, excepting the batch, I would still need a storage tank AND a method/pump to deliver, correct? The panels are about 100 feet vertically above the house. If the tank goes there as well, would this be enough for a gravity feed set-up? It's a small set-up, 2 panels. Are there pumps that would work with such a system? How much upgrade would be necessary?

    5. I am unclear as to how you can have the panels that high up ? You can make or buy pressure systems to boost water pressure, but then how much pressure do you need ? My system has a glycol loop going to the roof, and a seperate loop running with the house water pressure . . so its always at about 60 psi . . town pressure . . I have heard of people having a 60 gallon water tank right above their shower stalls and it provides a gravity feed - low pressure shower . . how much pressure do you need ?

    6) Any suggestions? Do you have any questions which I can answer or need to consider?

    More information on why the system is so far away would help, as well as how much water pressure is needed ?


    Thanks so much!
    dj
    2 - 255W + 4 - 285W PV - Tristar 60 amp MPPT CC / 3 - 110W PV -wired for 36V- 24V Sunsaver MPPT CC / midnite bat. monitor.
    1 KW PSW inverter 24V / 2.5 KW MSW inverter-24V ~ 105 AHR battery.
    3 ton GSHP.- 100 gallon warm water storage / house heat - radiant floor / rad
    9 -220W PV - net meter - Enphase inverters and internet reporting system.
    420 Gallon rain water system for laundry.***  6" Rocket Mass Heater with 10' bed for workshop heat.
    Current project is drawing up plans for a below grade Hobbit / underground home.
    Google "undergroundandlovinit" no spaces.
  • djdenali
    djdenali Registered Users Posts: 11
    Re: Solar Water Heater collector/system question

    SO, thanks to all. Questions put forth, Why are the panels so far from the house?--Because the house is too shaded for the panels. It is the only place with any long sun exposure without clearing lots of trees. Could we put an ICS (batch collector) up there and insulate the pipes really well to carry the heated water downhill to the shower? The inflow would be from a spring, so no need to pump the water back up. I am quite new to this whole realm, so my responses might seem ignorant. If so, I request patience. This set up seems to be the most simple. HOWEVER, we might be a light freeze a few times a year, but NEVER throughout the days, only at night.

    THoughts?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar Water Heater collector/system question

    The problem is you want small diameter pipes from the heater to the home so you don't have to dump gallons (or tens of gallons) of cold water and supply gallons of hot water just to heat the pipe.

    On the other hand, small diameter piping has higher resistance to flow.

    From this website (note that tubing is measured Outside Diameter and pipe is measured Inside Diameter--So 1/2 PEX OD is ~3/8" ID where as 1/2" copper pipe is >1/2 inch ID):

    Anyway, 3/8" ID PEX:

    0.5 gallons per 100' of PEX
    3 gallon per minute flow rate has 54 PSI drop per 100'.

    And 1/2" ID PEX:

    0.94 gallons per 100'
    3 gpm flow has 11 PSI drop per 100'.

    Of course, the larger the diameter of the pipe/tubing, the better flow but more wasted water (both cold and hot) for each usage.

    Somebody with more experience than I on plumbing and sending hot water a distance (underground).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Skippy
    Skippy Solar Expert Posts: 310 ✭✭
    Re: Solar Water Heater collector/system question

    Putting a solar water heater 100 feet away, fed by a spring, then run down hill to the house. . hmmm. . .you can have a batch heater, with a well insulated tank, but your still limited by distance. .
    I would say there are 2 things that would affect pressure. . .

    the size of the tank at the top of the hill :
    The larger the tank, the more pressure, but - the more energy (sun) you would need to heat the water (may not get hot enough if too big)
    The size of the pipe down the hill :
    Two small of a pipe and it won't run very good, too large, and you drain the tank of all the hot water, before it reaches the house. . .

    You have an interesting problem, its too bad you couldn't cut the top off of one of the trees, and use the tree trunk as your mounting pole ... so, cold water pipe from the spring - down the hill - up the tree- fill the batch heater - warm water is then gravity fed to the house. . . you could put in a 2 inch abs feed pipe for the spring, which would only pull water when you turn it on in the house once the tank is full, it stops . . . could even put in a small drain plug near the top of the fill pipe - before going into the heater , so when the weather does turn cold, the water will "trickle" out the drain hole - keeping the abs from freezing, since moving water does not freeze. . .

    Just a few random thoughts. . . I'm not an expert, just crazy :p
    2 - 255W + 4 - 285W PV - Tristar 60 amp MPPT CC / 3 - 110W PV -wired for 36V- 24V Sunsaver MPPT CC / midnite bat. monitor.
    1 KW PSW inverter 24V / 2.5 KW MSW inverter-24V ~ 105 AHR battery.
    3 ton GSHP.- 100 gallon warm water storage / house heat - radiant floor / rad
    9 -220W PV - net meter - Enphase inverters and internet reporting system.
    420 Gallon rain water system for laundry.***  6" Rocket Mass Heater with 10' bed for workshop heat.
    Current project is drawing up plans for a below grade Hobbit / underground home.
    Google "undergroundandlovinit" no spaces.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Solar Water Heater collector/system question
    Skippy wrote: »
    so when the weather does turn cold, the water will "trickle" out the drain hole - keeping the abs from freezing, since moving water does not freeze. . .

    Just a few random thoughts. . . I'm not an expert, just crazy :p

    The statement that moving water does not freeze is a questionable one. Sort of like a rolling stone gathers no moss. It depends on how fast it is moving.
    If the source water is warmer than freezing, then enough flow will bring in enough heat to keep the water temperature above freezing. How much flow that takes depends on the situation.
    If the source water is at the freezing point, then the downstream water will not freeze as long as it is moving, sort of a truism. But individual water molecules at the inside surface of the pipe can stop moving long enough to find some other similarly inclined molecules and freeze to the side. The rest of the water in the pipe keeps moving, but the ice layer gets thicker and thicker.
    Now when you get to the point that there is only a small hole left, then if the water flow is forced by a pump you may generate enough heat from turbulence to keep the temperature of the remaining water above freezing.
    Moving water in a river can freeze very nicely from the top down. Eventually, the flow may or may not get cut off completely and start to spill over the top of the ice instead. Or else the pressure will heave up the ice layer and break it. Physics and thermodynamics give you lots of options. :-)
    SMA SB 3000, old BP panels.
  • Eric L
    Eric L Solar Expert Posts: 262 ✭✭
    Re: Solar Water Heater collector/system question
    Why are the panels so far from the house?--Because the house is too shaded for the panels.

    At those distances, you might reconsider the design so that you're using electricity to heat the water via. something like a heat pump hot water heater. (This would not give you hot water for heating the house, only for water use -- I couldn't tell which you wanted).

    Normally, solar thermal is the first choice because it's so much more efficient. But over 100 feet, that efficiency advantage in is likely to be lost. A small electric heat pump system like a Nyle Geyser draws around 800 watts, which is a reasonable load for a moderately sized pv array.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Solar Water Heater collector/system question
    inetdog wrote: »
    The statement that moving water does not freeze is a questionable one. Sort of like a rolling stone gathers no moss.
    Moving water in a river can freeze very nicely from the top down. Eventually, the flow may or may not get cut off completely and start to spill over the top of the ice instead. Or else the pressure will heave up the ice layer and break it. Physics and thermodynamics give you lots of options. :-)

    So true. In fact the brook that feeds my turbine is all froze over and the only moving water is down near the bottom. I've also seen ice form on the rocks along the bottom in late winter. And I've also seen water break out and flow up over the top of the ice. Right now I can walk across the ice on the brook, but so far the turbine keeps going. Where the penstock is not underground, it's covered with insulating debris and snow.
    And yes, I've seen home water supplies freeze when the valve wasn't flowing water fast enough. Tricky stuff cold weather :)
  • Skippy
    Skippy Solar Expert Posts: 310 ✭✭
    Re: Solar Water Heater collector/system question
    inetdog wrote: »
    The statement that moving water does not freeze is a questionable one. Sort of like a rolling stone gathers no moss. It depends on how fast it is moving.

    I totally agree with you on that one. . . I figured that statement would get the science guys going ;) - yes, outdoors, in the "wild", moving water will freeze, and "overflow" itself just to keep running. . . but looking at it in this context, and growing up in a farm house - where the basement water pipes were ALWAYS freezing. . . you quickly learned that if it drops down to -20 tonite, leave the water tap on with just a slow dribble coming out. . . and the pipes will not freeze. . . even then, I still agree with you, that if it got cold enough, it would still freeze the pipe. . it would have to get awfully darn cold in your basement to do it though. . .:p

    Haven't you watched myth busters about that rolling stone/moss thing ? It does . .8)
    2 - 255W + 4 - 285W PV - Tristar 60 amp MPPT CC / 3 - 110W PV -wired for 36V- 24V Sunsaver MPPT CC / midnite bat. monitor.
    1 KW PSW inverter 24V / 2.5 KW MSW inverter-24V ~ 105 AHR battery.
    3 ton GSHP.- 100 gallon warm water storage / house heat - radiant floor / rad
    9 -220W PV - net meter - Enphase inverters and internet reporting system.
    420 Gallon rain water system for laundry.***  6" Rocket Mass Heater with 10' bed for workshop heat.
    Current project is drawing up plans for a below grade Hobbit / underground home.
    Google "undergroundandlovinit" no spaces.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar Water Heater collector/system question

    Moving water freezes, all Canadians know,
    It falls from the sky; they call it "snow".
    :p

    But seriously we do see "running" streams slow to a frozen halt as the temp drops lower. The mere fact the water is moving, even through a pipe, does not mean it isn't possible for it to lose heat fast enough to freeze on the fly.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar Water Heater collector/system question

    moving water creates heat from the friction applied to the movement, but this heat is not much and sometimes the fast moving water will be subjected to more colder surfaces faster causing heat losses that exceed frictional heat gains. bottom line is don't count on it not freezing.

    coot,
    most of us in the northern portions of the usa are very well aware of the snow as it is canada's no. 2 export to the usa with no.1 being the cold air.:p
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Solar Water Heater collector/system question
    most of us in the northern portions of the usa are very well aware of the snow as it is canada's no. 2 export to the usa with no.1 being the cold air

    You're welcome! 8)