Thermal Store and Condensing Boiler

Discussion in 'Plumbers' Talk' started by Ballcocks, Jan 9, 2005.

  1. Water Systems

    Water Systems New Member

    The reason manufacturers charge what might seem a
    disproportionate amount for a larger primary coil is
    probably a combination of factors...your standard
    cylinders are made in batches of 50-100 or so,
    bringing the usual economies of scale - to make a
    one-off will add significantly to the labour, as well
    as the cost of the added coil. If you demand so much
    extra coil that we are forced to use finned coil,
    then this is itself hellish expensive compared to
    standard tube.

    I have asked for extra tappings on some standard cylinders and the xtra expense has negligible. Range have a comprehensive list of cylidner types with various tappings about.

    The extra cost for some cylinder coils has led me to use a plate heat exchanger and pump, and just screw them on - and improve efficiency.

    What I find rip off with cylinder companies is the hype in price for an immersed coil thermal store, which is on their catalogue, which is basically a cylinder and larger coil, and in most case not too dissimilar to their quick recovery coil standard indirect ranges.
     
  2. olfert

    olfert New Member

    r2d2
    I used a lot of mild steel storage tanks from 1000litres up to 4500litres primarily for heating commercial growing beds (nursery's) a couple of hospital laundrys too, using gas or electric as primary heat source, sometimes with solar boosting. The water was stored at 75 C and the pH was controlled with tannin based treatment (Gentex I think) these tanks are still operating. some after nearly 20 years (well nobody's chasing me anyway)my recollection is the the smaller tanks were 2mm thick and the larger 3mm
    regards
    TOF
     
  3. Water Systems

    Water Systems New Member

    And since I'm here r2d2, if this house is for you
    forget the solar panels and consider ground source
    far better with a cop of 4-1


    Doi.
    A Ground source heat pump is being considered

    Think Hard.......

    On average heat pumps consume one third of the electricity of electric resistance heaters.

    Economy is improved by operating heat pumps using overnight off-peak electricity, storing heat in a large thermal-store of water to be used during the day.

    Efficiency

    This is slightly confusing, as there are three efficiency acronyms to note: COP, SEER and HSPF. The COP is the important figure. The COP - Coefficient of Performance, based on kW of electricity consumed and kW of heat produced.

    Performance – COP

    The COP relates to electrically driven heat pumps. The efficiency performance rating is the Coefficient of Performance, the COP. As a guide, electricity is 100% efficient in that all the energy used at point of use is converted to power or heat. An electric immersion element heating a hot water cylinder has a COP of 1. A natural gas boiler will be approximately COP 0.85. The higher the COP the more efficient the heat pump. A COP 4 rating means that for every kilowatt of energy consumed four kilowatts of heat is extracted. Some manufacturers are claiming COP 7.

    Generally, heat pumps with the highest SEER and HSPF ratings are more expensive to purchase. However, because of low electricity consumption, economics in the long-term are more attractive.

    Ground Source Heat Pump

    Geothermal heating and cooling. Heat is extracted from the ground, which has predictable stable temperatures. Conversely, heat may be dumped into the ground when cooling a building. Heat is extracted by installing a plastic pipe loop horizontally or vertically in the ground. Ground-source heat pumps work well no matter what the air temperature, because the ground temperature does not drop much below 10C in the United Kingdom at a depth of 1.3 metres. Incorrectly designed or sized pipe loops can over-cool the ground surrounding the pipe, leading to much lower outputs and efficiencies.

    It is possible to freeze the ground around a ground loop lowering efficiency. It is preferably to have inactive periods to allow the ground temperature to recover preventing ground freezing. When the temperature of the ground is lowered sufficiently, the COP rating will drop.


    Using three to four times less electricity to run than conventional electrical systems, on the surface appears highly attractive. However, appearances can be deceptive. Running costs are likely to be higher than a condensing gas boiler system when used for heating purposes. The best case example of a water sourced heat pump may equal or slightly improve on natural gas running costs. Despite a gas boiler having a COP of 0.85 and a heap pump say COP 3, natural gas per kWh is approximately 4 times cheaper than electricity. Running cost comparisons to oil depends on oil prices, which may fluctuate greatly depending on the season and world demand. Overall, heat pumps cost more to run than an oil boiler.

    Although a heat pump may equal the running costs of a natural gas boiler, in the UK the big problem is the extremely high installation costs, which may be three to four times the cost of a typical gas fired system. Heat pumps as yet, cannot compete with the installation costs of boiler and forced-air heat recovery and ventilation systems fuelled by the three main fuels of natural gas, oil and liquid petroleum gas (LPG).
     
  4. Scousemouse

    Scousemouse New Member

    Really good post WS :)
     
  5. goldfish

    goldfish New Member

    Are there any particular pointers to watch out for regarding thermal stores and limescale?
     
  6. Water Systems

    Water Systems New Member

    Are there any particular pointers to watch out for
    regarding thermal stores and limescale?

    No more than any other system. If you have limesacle you should take precautions against it - with any system.

    Specifically to thermal stores.

    Thermal Store

    These days a thermal store is a cylinder with an immersed DHW take-off coil with fresh water running through the coil.

    Heat Bank

    A cylidner using an external plate heat exchanger and pump, to pump the primary hot water from the cylinder into ther plate is termed a heat bank. Two sisters.

    The stored water is primary and as long as enough inhibitor is used, and re-dosed every 3 to 4 years, there is no problem with sludge or limescale. The small DHW section, containing fresh water, may scale up. This can be de-scaled by using appropriate descalling fluid in the coil of the thermal store. Two full-bore valves, top and bottom of the coil, a drain and a filling point would help here, making it a DIY job. The heat bank resists scale formations by the stainless steel plates in the plate heat exchanger flexing. If scaled up, it is a matter of turning off the main stop cock, removing the plate by unscrewing four unions, de-scaling by using appropriate fluid, and screwing back on. Again not beyond the scope of a DIYer. In fact very sinmple indeed.

    With a conventional system, where the stored water is fresh water, the inside of the cylinder and exterior of the coil become caked with scale, and de-scaling then is a much bigger job, to the point that if professionals are required, it is more cost effective to replace the cylinder in many cases. DIYing, may mean spending £80 on an identical cheap screw-in, screw-out cylinder, with a one year guarantee and no corrosion, or £50 on de-scaling fluid.
     
  7. Water Systems

    Water Systems New Member

    As far as square tanks go - their advantage is that
    for the same height of tank, you can store more
    water,

    Not only that they can go in the top or bottom of a cupboard fitting exactly, saving much space.

    but when you bend the copper sheet in a tight
    90 degree bedn, you stress it - almost all corrosion
    within elson tanks (the ones I have seen and replaced
    anyways) takes place at the corners - where it is
    stressed.

    Using square tanks as a thermal store this is not so much of a problem. Appropriate inhibitor will resist corrosion. Fresh water may be corrosive and attack the weaker corners.

    I like Elson products - they have the tansk and F&E tank all integrated into the main tank, which saves much space. The last time I looked they still were using thermal stores with coils, in square tanks. Plate heat exchangers are far better when using square tanks, and I don't know why they have not gone over to this method - they may have by now.
     
  8. changename-12753

    changename-12753 New Member

    Watersystems.
    A lot of Geothermal heat pump manufacturers are using PHE. Their are specially designed gasketed PHE available for duties involving evaporation and condensing sysyems. Hot gas on the primary side. Gas to liquid heat exchange in other words.
    The shell and tube type bundle heat exchangers are used extensively in water-chill applications.
    I think the pressure drop factor through these exchangers and a number of other attributes makes them more suitable for gas to liquid applications.
    Could they be adopted and used in the small Geothermal heat recovery system successfully.?
     
  9. Water Systems

    Water Systems New Member

    Watersystems.
    A lot of Geothermal heat pump manufacturers are
    using PHE. Their are specially designed
    d gasketed PHE available for duties involving
    evaporation and condensing sysyems. Hot gas on
    n the primary side. Gas to liquid heat exchange
    in other words.
    The shell and tube type bundle heat exchangers
    are used extensively in water-chill
    applications.
    I think the pressure drop factor through these
    exchangers and a number of other attributes
    s makes them more suitable for gas to liquid
    applications.
    Could they be adopted and used in the small
    Geothermal heat recovery system successfully.?

    I see not reason why not. It is a matter of contacting the makers, like GEA, and they will advise a suitable plate and size.
     
  10. goldfish

    goldfish New Member

    Thanks to Watersystems for replying to my limescale enquiry.
     
  11. Water Systems

    Water Systems New Member

    If you demand so much
    extra coil that we are forced to use finned coil,
    then this is itself hellish expensive compared to
    standard tube.

    CCM, where is finned tube available? I need a little to experiment with.

    WS
     
  12. Stoday

    Stoday New Member

    Suggestion - try a car radiator refurbishment company.
     
  13. RenewableEnergyMan

    RenewableEnergyMan New Member

    WS - how much is 'a little to experiment with'?

    The stockholders sell it in 50 x 6m length boxes. The merchants are unlikely to stock it.

    I have loads in stock in 6m lengths and some off cuts in smaller lengths - what do you need?

    carriage might be a bugger though :) - although we could coil it for you .

    CCM
     
  14. Water Systems

    Water Systems New Member

    WS - how much is 'a little to experiment with'?

    The stockholders sell it in 50 x 6m length boxes. The
    merchants are unlikely to stock it.

    I have loads in stock in 6m lengths and some off cuts
    in smaller lengths - what do you need?

    carriage might be a bugger though :) - although we
    could coil it for you .

    CCM

    I thought as much, more a wholesale item. I can recycle some. It is to paint matt back and insert at the top of a conservatory and use to naturally circulate the conservatory heat and heat a cylidner on a room above - for free.

    My calcs show it can be done. The temperature at the top has been measured at over 65C. Calcs are one thing and real life is another.

    Alos an air heater inside the conservatory with the finned tube inside is very efficient. Solar air heaters can scorch they get so hot and produce more heat than conventional roof mounted wet solar collectors.
     
  15. olfert

    olfert New Member


    My calcs show it can be done. The temperature at the
    top has been measured at over 65C. Calcs are one
    thing and real life is another.

    Alos an air heater inside the conservatory with the
    finned tube inside is very efficient. Solar air
    heaters can scorch they get so hot and produce more
    heat than conventional roof mounted wet solar
    collectors.

    Water Systems have you thought about a vacuum heat pipe(s) copper tube, finned or not, directly into the tank .. no pump required. As long as there is a delta T available you would get contribution. There is a fairly easy way to make a copper heat pipe by boiling an amount of water inside the pipe and then sealing it off when steam comes out creating a vacuum in the pipe.
    It would depend on the layout but as long as you have a reasonable fall on the pipe for the condensate to run back down it will work.

    regards
    TOF
     
  16. Water Systems

    Water Systems New Member


    My calcs show it can be done.
    The temperature at the top has
    been measured at over 65C. Calcs
    are one thing and real life is another.

    Also an air heater inside the
    conservatory with the finned tube
    inside is very efficient. Solar air
    heaters can scorch they get so
    hot and produce more heat than
    conventional roof mounted wet solar
    collectors.

    Water Systems have you thought about a vacuum heat
    pipe(s) copper tube, finned or not, directly into the
    tank .. no pump required. As long as there is a delta
    T available you would get contribution. There is a
    fairly easy way to make a copper heat pipe by boiling
    an amount of water inside the pipe and then sealing
    it off when steam comes out creating a vacuum in the
    pipe.
    It would depend on the layout but as long as you have
    a reasonable fall on the pipe for the condensate to
    run back down it will work.

    Anything vacuum is expensive. A line of 22mm finned coper tube painted matt black along the top of the cosnervatory will heat the bottom of a cylinder or a pre-heat cyldiner. The conservatory is facing south, so maximum solar exposure. It also gets hot in winter in there. All gravity and as long as there is a temp differential it will work, so the only complexity is a zone valve on the return vertically mounted and a diff controller. Cheap and works. Other ways will work better, but at a cost.
     

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