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Heating and cooling: Drain-back Solar Panel system

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  1.  
    • CommentAuthorGreenPaddy
    • CommentTimeFeb 16th 2010
     
    I am currently spec'ing the solar hot water system for my soon to be new-build house, and am considering a drain back system - apparent simplicity, no antifreeze/risk of freezing (in the Scottish Highlands). My assumption is;

    - circ pump on the return from my therm store (to the collector)
    - small breaktank on the flow side (in roof void, after collector outlet)
    - check valve on flow to therm store (close to the therm store)
    - temp probes/controls (already fairly well sorted for these I think)

    Would appreciate comments as to problems with drain back types; am I over simplifying? Are there examples of these on the web that I could steal the design from (I mean pay all duely deserved royalties).

    Have read about the trickle back noise, but think I could overcome this.

    Thanks, GreenPaddy.
    • CommentAuthortychwarel
    • CommentTimeFeb 16th 2010
     
    I have a drainback system from Filsol down here in south wales and have no problems with noise. Thier website has an outline drawing showing component layout.

    ps you will still need a corrosion inhibitor/antifreeze.

    Paul
    • CommentAuthorcrusoe
    • CommentTimeFeb 17th 2010
     
    I second tychwarel's comments, never had any real problems with drain-back. They are to solar, problems-wise, what the Fergie is to tractors. Simple, robust, and no particular problems. If done properly of course...and as noted, with an antifreeze/inhibitor combo. Fernox's Alphi 11 is the ubiquitous choice.

    I have used Filsol a number of times. Good kit, robust, modular and simple, but not your usual flat panel. Performance approaching ET, but with a 30 year life.
    • CommentAuthorbella
    • CommentTimeFeb 17th 2010
     
    I like the concept of drain back and have a couple of (probably daft!) questions. Does the system "drain back" every evening and then have to be refilled each morning, or just when it gets too hot or too cold for safety? Why is anti-freeze needed?

    Installers (two I have approached) don't seem to like drainback and don't offer it. Is it a lot more taxing to get the "draining" right than in a standard system?
    • CommentAuthorJeff B
    • CommentTimeFeb 17th 2010
     
    I can concur with the comments of tychwarel and crusoe, as I also have Filsol panels with a drainback system. The water contains Fernox Alphi 11. I've never had any problems with drainback but I must say I honestly don't know if the system has ever drained back, as I don't think the panels have ever got too hot. How would I know if this was occuring? Noise?
    • CommentAuthorunguided1
    • CommentTimeFeb 18th 2010
     
    I once installed a ferroli aquacyl solar system in a bungalow and the customer wanted the solar cylinder put in the same roof space as the solar panel was installed on, and the only issue we had was making sure that there was enough height between the bottom of the panel and the inlet on the solar coil in the cylinder.
    Apart from that everything is working well .
    • CommentAuthortychwarel
    • CommentTimeFeb 18th 2010
     
    Drainback systems have a small insulated tank normally situated just below the bottom of the panel. when the circulation pump isn't running the water all drains out of the panel and into this tank.

    As soon as the controller switches the circulation pump on. It pumps water from this tank into the panel where it then circulates to the hot water tank /thermal store.

    If the system is running properly you wouldn't notice it draining back.

    The principal reason for the Fernox is a corrosion inhibitor but in the event your roof space freezes it makes sense for it to be an antifreeze as well.
    • CommentAuthorJeff B
    • CommentTimeFeb 18th 2010
     
    Tychwarel - I thought the drainback system only operated if the panels got too hot during the summer months? We have only had the use of the Filsol panels for one summer so far and if you recall the weather last summer there was little danger of them overheating!

    So as soon as the circulation pump stops then, the fluid drains back into the insulated tank in the loft. If I ever knew that, then I have forgotten it! Hence as you say I haven't noticed the system draining back because presumably it is all working normally.

    As an aside, whereabouts in South Wales are you? We are in Pembs.
    • CommentAuthortychwarel
    • CommentTimeFeb 18th 2010
     
    location Treharris
  10.  
    Viridian Solar have drainback systems which operate with a glycol mixture, apparently for belt and braces protection against freezing.

    PAW produce an interesting drainback system, curiously named DrainBloC, which can be used with either panels or evacuated tubes.

    At the risk of stating the obvious, more care has to be taken with levels and pipework than with a fully filled system to ensure that it really does drain back!

    At least one panel manufacturer notes that their panel "is not intended to be used in drain-back systems". So some care may be needed in choosing suitable equipment.
    • CommentAuthorJohn B
    • CommentTimeFeb 19th 2010 edited
     
    I used to be involved in installing Imagination Solar drainback systems. The drainback tank and circulating pump is in a combined unit mounted on the floor below the hot water cylinder. All pipework needs to be on at least a slight downward slope from the panel.

    When the pump isn't running, all the water is in the drainback tank, so there is no water the the panel or pipework.

    When the pump starts, the water in the drainback tank is circulated.

    When the pump stops, all the water drains back into the drainback tank.

    We never used any additives in the water, unless it wasn't possible to have the entire pipe run sloping downhill.

    This was a few years ago, so I don't know if the current systems are the same.

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