Normal/Max temperature - open loop solar heat

pcguy2upcguy2u Posts: 139Solar Expert ✭✭✭
I'm breaking in a new solar water heating system and need to establish a norm for different conditions.

I think I was expecting something on the order of 170+ degrees, but that never happens unless the pump is turned of for a short while and of course, it soon lowers to the then 140 degree norm (this is for a 68 degrees sunny day with a little wind in Bodega Bay CA). It came to the temp at about noon today. Is 140+- degrees on a day like today an ok result, or?

I would appreciate knowing what the nomal high temperature one can expect on different types of days along with what time of the morning the temp comes up to that degree.

Many thanks,
Nick

Comments

  • mike95490mike95490 Posts: 7,971Solar Expert ✭✭✭✭
    Re: Normal/Max temperature - open loop solar heat

    It's not the outlet temp you should be looking at, it should be your storage tank temperature.
    The more "delta" between the inlet and outlet of your collector, the more losses you have.

    The hotter you can get your STORAGE tank, the better off you are. After a long sunny day (and the end of June, begin of July are the longest) you should be able to scald yourself from the storage tank. Since that result is painfull, it would be a good time to:
    A) run the dishwasher
    b) do some white laundry
    c) wash the dog

    Use up some of your heated water midday, so the system has some hours left to recover and heat some more water to use at night.

    This is all variable with your type of system, but just storeing hot water, is wasted. You gotta use it while it's hot, and while it can reheat.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • pcguy2upcguy2u Posts: 139Solar Expert ✭✭✭
    Re: Normal/Max temperature - open loop solar heat

    I agree with what you say Mike, I just trying to find out that my 140 degrees is a good number.

    Thanks for your thoughts,
    Nick
  • icarusicarus Posts: 5,108Solar Expert ✭✭✭✭
    Re: Normal/Max temperature - open loop solar heat

    It all depends on the Delta T as Mike suggests. It has been a while since I have done any water heat calcs, but if memory serves, the most efficient collector is one that circulates the water with a MINIMUM Delta T. So if the tank temp starts @55f, and comes out 140f you obviously have a significant temp rise. On the other hand if it is coming out of the tank @125f ,,,,

    What then becomes significant is the flow rate. The only thing that matters in the real world, is if you are getting enough hot water. Would you rather have a smaller volume of water that is hotter, or a larger volume that is not so hot? Not to argue with Mike, it seems the best situation is one that heats the water almost to use temp, perhaps a bit above. I would rather have 50 gallons of 100f water, and have to heat it to ~105 for the shower, AND have the capacity for several showers, than 20 gallons of 140f water. You could do a calc, and see which contained more BTU's, but the losses would be less in the cooler tank AND you would have a bigger reserve.

    The bottom line is Total number of BTUs IN the water, by the time you use it.

    Tony
  • System2System2 Posts: 6,290 admin
    Re: Normal/Max temperature - open loop solar heat

    The temperature you will get is directly related to the insolation levels (sun energy) and the adility of your solar collectors to convert the sun energy to heat.
    Other factors include-
    The size of your solar system
    The angle of your collectors to the sun
    The efficiency of the solar collectors

    The most important part of the whole solar system is the storage (insulation of the storage cylinder) so as long as the differentual controller is doing its job the solar collectors will be contibuting to the total heat stored. (It is gererally cheaper to pump water than to heat water)

    Cheers
    Ian
  • BB.BB. Posts: 28,090Super Moderators, Administrators admin
    Re: Normal/Max temperature - open loop solar heat

    Ian,

    Welcome to the forum!

    I am not sure what you are trying say/ask here--The solar thermal panel design and the system's upper working temperature are important factors here...

    For example, one of the most efficient solar panel you can get is one of those simple plastic panels used to heat swimming pools.

    The are very good because the maximum temperature required to heat a pool is just about equal to the surrounding air temperature--so no insulation required and virtually no heat loss...

    For a domestic hot water system, you need hotter water than can be efficiently supplied by a simple flat plastic collector. So, you need an insulated box with glass top to get the higher temperatures. Less efficient, but better suited to the task of heating water above ambient air temperature.

    There are also very high-technology vacuum thermos type collectors--work very well in heating water very hot in cold temperatures...

    But, interestingly, I was reading elsewhere that the vacuum technology tubes may not be best for areas that get snow... The glass box gives up more heat (because it is not as well insulated at the vacuum tube type) and melts snow from the panels--where the vacuum type would just let the snow remain and prevent solar absorption...

    There are also other considerations, collector angles to optimize winter heating and prevent overheating in the summer. And lots of other design issues (no freeze, soft freeze, hard freeze, etc.)...

    Where do you want to go from here?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • pcguy2upcguy2u Posts: 139Solar Expert ✭✭✭
    Re: Normal/Max temperature - open loop solar heat

    Maybe I should have phrased the question differently - all theoreticals and personal preferences aside?

    Would anyone care to post the normal high temperature of water coming from their collectors that they use for heated water from the sun?

    Just some numbers would be helpful.

    Thanks again,

    Nick
  • mike95490mike95490 Posts: 7,971Solar Expert ✭✭✭✭
    Re: Normal/Max temperature - open loop solar heat
    pcguy2u wrote: »
    Would anyone care to post the normal high temperature of water coming from their collectors that they use for heated water from the sun?

    It should be close to the system designer's calculations.

    It should never be above the collectors "do not exceed" spec.


    Sorry, you still have not got the question right. How hot I like my shower, or how cold I like my ice cream, should not, in a free society, affect your choices at all.

    As long as the storage tank has water hot enough to shower with in the morning, would be fine by me.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • icarusicarus Posts: 5,108Solar Expert ✭✭✭✭
    Re: Normal/Max temperature - open loop solar heat

    My simple, homemade flat plate collector, (copper pipe loop, on top of 3/16 plate steel in a glass covered box, circulating ~ 3 gpm) starts out with a Delta T of about 3 degrees F. It maxes out at about 135f. After that it starts losing more heat than it can pick up. As I said before, the out put temp doesn't mean much, unless you know the flow rate and the Delta T. It's Btus into the water that matters.

    Tony
  • pcguy2upcguy2u Posts: 139Solar Expert ✭✭✭
    Re: Normal/Max temperature - open loop solar heat

    Thank Tony, exactly what I was looking for..........

    n
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