Preheating water inlet to geyser




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  1. #1
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    Default Preheating water inlet to geyser

    I want to preheat the cold town water before it enters my geyser.
    There is a solar type heating system in the classifieds for sale.

    If I were to connect this up and let the town water flow through the 2 collectors before it hits the geyser will it effectively preheat the cold water that comes into the geyser?

    Its rated as 100kpa, what pressure is town water connection and will the town pressure "push" the water through the 2 collectors into the geyser?

    Any input welcomed please...
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  2. #2
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    Default Re: Preheating water inlet to geyser

    Quote Originally Posted by NewLandy View Post
    If I were to connect this up and let the town water flow through the 2 collectors before it hits the geyser will it effectively preheat the cold water that comes into the geyser?
    It might work, but only if the cold water coming into the geyser only comes in during daytime when the sun shines on the panel, probably working best during the 10:00 to 15:00 period, so no benefit to my 6:30am shower for example.

  3. #3
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    Default Re: Preheating water inlet to geyser

    Just bought a house off plan with a heat exchanger/heat pump installation.

    It heats the water and pumps it through the Geyser.
    It does not operate in tandem with the Geyser. It's only or just the heatpump or just the Geyser.

    Is this the type of solution you are considering?
    Last edited by swakop_toe; 2018/05/26 at 10:04 PM.
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    Default Re: Preheating water inlet to geyser

    Quote Originally Posted by NewLandy View Post
    I want to preheat the cold town water before it enters my geyser.
    There is a solar type heating system in the classifieds for sale.

    If I were to connect this up and let the town water flow through the 2 collectors before it hits the geyser will it effectively preheat the cold water that comes into the geyser?

    Its rated as 100kpa, what pressure is town water connection and will the town pressure "push" the water through the 2 collectors into the geyser?

    Any input welcomed please...
    No

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  6. #5
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    Default Re: Preheating water inlet to geyser

    Quote Originally Posted by plunger View Post
    No
    Why not. Solar geyser panel systems are piped into the geyser tank. The element is there as a back up.
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    Default Re: Preheating water inlet to geyser

    Short answer is No. Normal geysers run at 400 or 600 kpa and the water would flow through the collecters too fast to gain any significant heat.
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  9. #7
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    Default Re: Preheating water inlet to geyser

    Quote Originally Posted by plunger View Post
    No
    ^^ what he said ^^


    Solar panels are PART of the geyser installation, thus PART of the pressure relieve valve when the water boils in the panels.

    The water boils rather quickly in the panels, THUS the reason for circulating water between the panels and the geyser, to store the heat in the geyser ... even so, many solar systems still reach boiling point by lunch time .....


    short answer - NO, those panels will pop if not piped into the geyser with its pressure release valve ....

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  11. #8
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    Default Re: Preheating water inlet to geyser

    The water in the panels are circulated from the geyser through the panels back to the geyser at a very low flow rate by either thermosyphoning or by use of a pv drivin pump.
    In so doing gradually heating up the water in the geyser vessal.
    If you use geser water during the day, you continually add cold water to the geyser from main supply thus cancelling out any heat generated by the panels.
    If you want to pre heat the water entering the geyser you heve to connect a solar geyser in series to the second geyser.
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  12. #9
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    Default Re: Preheating water inlet to geyser

    I have seen two methods that could be considered to preheat the water. The first one is actually used as the only "geyser" in some holiday places. Large pressurized black tank in a sunny spot. Geyser gets the water from the tank. Second installation that I saw was to boost up the hot water supply. Large non pressurized tank standing next to a communal bathroom. Water was heated using simple solar panel/s. From there water was pumped to the geyser.

    I doubt that either make economical sense but in specific situation can be the only workable solution.
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  13. #10
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    Default Re: Preheating water inlet to geyser

    I found this pdf ...Option 3 is what I was thinking about.

    So it looks like you cant just put it between your cold water inlet and the geyser, it must be plummed into the system like the various threads have stated.

    Its not just a solar collector, its also a "built in" geyser as well...

    I" ll phone around on Monday and see what / where they have been installed. Maybe it was an experiment that failed..........
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    Last edited by NewLandy; 2018/05/27 at 09:03 AM.

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    Default Re: Preheating water inlet to geyser

    I looked into that Solo. It is pressurized but the shape of it is not the best. Worth to investigate a bit more to see that it really can take the pressure. From pressure point of view ball shape is the best. Plastic loses its strength very quickly with increasing temperature.

    With this and all other "pre-heaters" the night temperature issue should be looked at. Where the night time temperature is very low system can turn to be counter productive.
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  15. #12
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    Default Re: Preheating water inlet to geyser

    I got a quote for the installation and supply of a 150l solar geyser with tubes setup in series with existing elec geyser. R20K! Installation is R7500 excl!

  16. #13
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    Default Re: Preheating water inlet to geyser

    I looked at this solution and decided to opt for 20 Lt gas geyser, full installation for R10K
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  17. #14
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    Default Re: Preheating water inlet to geyser

    You will waste your money. The problems as mentioned are:
    1. During the day very little hot water is used, so heat build-up in solar panel only
    2. Due to 1. the water in the panel would boil and result in pressure built up
    3. Municipal pressure is much more than 100kpa
    4. During the evenings/mornings when bulk of hot water is used, you would pre-cool your water feed
    5. Even if hot water is used during sunshine hours, the flow would be so high that little heating takes place
    6. These panels are prone to freezing in winter
    7. If the panel pops due to 2., 3. or 6. the cost of water wasted will be substantial

    I have installed an alternative solution, but it also has its problems:
    Low-pressure (as seen in informal settlements) 150l solar geyser. Hot water is feed to pressure pump and then to (cold) inlet of geyser. It worked, but the following issues should be considered:
    - Pressure pump must have heat resistant impeller
    - Pressure pump bearings fails regularly (2 years)
    - Noise factor of pressure pump
    - Electricity consumption of pressure pump
    - Aesthetics: it looks ugly

  18. #15
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    Default Re: Preheating water inlet to geyser

    Just my view:

    Quote Originally Posted by LouisF View Post
    You will waste your money. The problems as mentioned are:
    1. During the day very little hot water is used, so heat build-up in solar panel only
    (this is the idea of a solar Pre heater, to feed hot water to an existing electrical geyser, thus using less energy to heat the electrical geyser)

    2. Due to 1. the water in the panel would boil and result in pressure built up
    (Vacuum tube solar heater with glycol can't boil in the collector, there is no water in the collector, for the pressure build up ensure your regulating valves are correctly sized)

    3. Municipal pressure is much more than 100kpa
    (You need your pressure regulator sized according to the solar and electrical geyser, 400 or 600kpa, if not this will cause unbalanced pressure resulting in sudden cold spurts in the shower!)

    4. During the evenings/mornings when bulk of hot water is used, you would pre-cool your water feed
    (Solar geysers has 50mm insulation, you won't Pre cool, you will still pre feed with around 40deg water, which means you still save money, the degrees can be higher but it depends on the lifestyle of the household)

    5. Even if hot water is used during sunshine hours, the flow would be so high that little heating takes place
    (Solar geyser as a pre-heater isn't a collector panel as per heater, it's a 150L tank heated by the sun through vacuum tubes with glycol inside. You could also use the spiral coil system, so during sunshine hours you could feed the geyser with 60deg plus water.)

    6. These panels are prone to freezing in winter
    (Again 50mm insulation on the geyser and the vacuum tubes with glycol won't freeze, it's basically anti-freeze, the thermosyphon system are prone to freezing as there is water in the tubes)

    7. If the panel pops due to 2., 3. or 6. the cost of water wasted will be substantial
    (Vacuum tubes can break and no water will leak, as the water does not flow in the tubes, however water does flow in the thermosyphon systems tubes. Vacuum tubes are also tested with simulated hail stones of 30mm in diameter flying at 52km/h.)

    I have installed an alternative solution, but it also has its problems:
    Low-pressure (as seen in informal settlements) 150l solar geyser. Hot water is feed to pressure pump and then to (cold) inlet of geyser. It worked, but the following issues should be considered:
    - Pressure pump must have heat resistant impeller
    - Pressure pump bearings fails regularly (2 years)
    - Noise factor of pressure pump
    - Electricity consumption of pressure pump
    - Aesthetics: it looks ugly
    (I don't know who advised you to install a low pressure system, go kick him in the hooha!)

    My 2c: A properly sized and installed solar geyser or Pre heater will save you money. Yes it's a big investment but calculate the long term savings.
    I like the preheater systems as it increases your total hot water capacity.
    Don't ever install a low pressure geyser in towns or cities.

  19. #16
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    Default Re: Preheating water inlet to geyser

    My 2 flat panels are connected to 2 150l geysers and the pump circulates through both geysers.
    Control is via a Geserwise and one cylinder has an element for early morning and afternoon/evening backup when the weather is unfavourable.
    This morning, my water is at 42 degrees.
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  20. #17
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    Default Re: Preheating water inlet to geyser

    I installed a Heatbox (preheater) and geyserwise controller and never looked back---My geyser receives warm--hot water and controller set at 50 degC--My elect bill came down from 2100 to 850
    Last edited by Mark Sanderson; 2018/06/08 at 05:52 PM.
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