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Green Building Bible, Fourth Edition
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    • CommentAuthorrevor
    • CommentTimeFeb 21st 2020
    Have been operating a solar thermal system for a few months now and whilst I cannot quantify the contribution it makes in kwh I am impressed on a sunny (infrequent this winter) day how much it adds to the thermal store temperature. A couple of weeks ago we had a good sunny day and we did not need the heating on at all that evening. We have a lot of solar gain built in as well which helps.
    It is fairly automated in that when the differential between the panel and store is 6 deg or greater the pump starts circulating. When the differential is 4 it stops.The display shows a % pump speed which is decided by the controller. The only control I have over the circulation is the manual pump speed for which there are 3 settings.
    I have, when I am about, tried to keep the differential temperature as big as possible by dumping the heat in the coldest room of the UFH, the logic being that I ensure that I store as much heat as possible i.e. in the floor and in the tank. In other words keep the system running. That bit seems to work well. What I cannot work out is what would be an optimum pump speed setting for the pump. I have tried experimenting but the collector panel temperature is never constant up and down with position of the sun and clouding over etc.
    Has anyone got any ideas how I can get more out of the system by operating differently?. There are possibilities of changing parameters within the controller but with not understanding how it works have not explored that possibility. Bottom line off course cannot get more than the sun is willing to give.
    • CommentAuthorgyrogear
    • CommentTimeFeb 21st 2020
    Perhaps post the controller type, and hyperlink to technical manual, if you have one.

    • CommentAuthorrevor
    • CommentTimeFeb 23rd 2020
    Thank you. It is a Velux system. Have a manual but cannot find it on web. Plenty of install instructions. Manual has chapter on setting adjustable parameters but do not make much sense at moment other than obvious e.g alarm settings. Some general thoughts to give me some direction would be useful. The system is no longer available in the UK but seems to be obtainable elsewhere.
    • CommentAuthortony
    • CommentTimeFeb 23rd 2020 edited
    I have a bespoke control system with two panels, two cylinders two pumps and a heat dump from the second (pre heat hw cylinder) to my interseasonal store. I also have electronic frost stat.

    The optimisation is via using a 3C temperature difference between panels and whichever cylinder is demanding heat. Once triggered the pump runs for 12 mins and only continues if the difference is greater than 3C, otherwise waits til it is, once solar cylinder is up to 45C the pre heat cylinder is heated to 40 and after that heat is dumped into my interseasonal store.

    I have solar PV and excess is diverted to the top of the hw cylinder to bump it from normal 48C to 55C

    Ideal solar control involves movement of the slug of hot water from the top of a panel into the cylinder and leaving it in the coil to heat the cylinder and so in a batch process. This is almost impossible to control so pumps run more continuously like yours. I think 4C is a bit much to be optimal. How long to run the pump and how fast have yet to be discussed

    In very hot blue sky days my pumps run on slow almost all day
    • CommentAuthorMikC
    • CommentTimeFeb 25th 2020
    <blockquote><cite>Posted By: revor</cite>What I cannot work out is what would be an optimum pump speed setting for the pump. I have tried experimenting but the collector panel temperature is never constant up and down with position of the sun and clouding over etc.</blockquote>

    The optimum pump speed is variable depending on the solar input and you want to gather heat at as low temp differential as possible if efficiency is your aim. You can get variable flow rate controllers but they require a flow sensor and variable pump. I've not used one but I suspect they will be expensive, resol used to do one but I haven't seen their offerings for many years now.

    If you have a fixed speed pump like most setups, aim for about 2 litres per minute per sqm of panel (flat plate, a bit more for evac tubes), assuming you have a flow guage in line.
    • CommentAuthorGreenPaddy
    • CommentTimeFeb 26th 2020
    I think what you're looking for is to control the flow water temp to a constant value (ish), by varying the volume of water.

    Your controller needs to have a PWM output (will be on the low voltage side of the wiring block). You then need a PWM pump, which are about £50 more than a standard circ pump. It will have a little plug port to accept the PWM cable (that's in addition to the 240V power input).

    The controller would then be set into PWM mode, and a fixed deltaT value input, which sets the flow water temp to be controlled at that deltaT above the "switch on" or "deltaT ON".

    Clear as mud? I find most solar control manuals very confusing, even though I've read quite a few. I reckon they are written by GCHQ, to confound and confuse. Or use as few words as possible to save paper, and then give you copies in 37 languages...:cry:
    • CommentTimeFeb 26th 2020
    A good subject for AI - the system could learn for itself!
    @revor, what is your objective? Do you want loads of lukewarm water to heat the house, or just enough piping hot water for everyone to have a shower?
    • CommentAuthorrevor
    • CommentTimeFeb 26th 2020
    Thank you all round The pump on the system seems to vary automatically by the controller programme but do not know what parameters it uses to decide what speed it should run at or how it does it as it is not a PMA. It displays as a % pump speed which changes with temperature although have not studied whether it is differential temp or collector temperature. The pump has external pump speed 1 2 3. Control cannot be via flow meter as whilst it has a manual flow readout there is no input to the controller so can only surmise it must be controlling pump via flow and return temperatures unless the pump does not vary but would do if it was a PMA. There are no inputs into the controller other than the measured temperatures in the store. The discussions have raised the fact I need to carry out some studies on how my system is controlling e.g does the flow change with changing pump speed on the readout or as a function of temperature differential.
    In terms of what I want out of the system it is to be able to extract as much heat out of the sun into the tank regardless of what it will be used for.
    It would have been useful if the manual explained how the system worked maybe I could make more sense of working out how to get the best out of it. Perhaps it has already been optimised and am wasting my time unless I up the hardware as suggested in the discussion.
    • CommentAuthorGreenPaddy
    • CommentTimeFeb 28th 2020
    Deff read the instructions repeatedly, until you decipher. It will become clear. A few possible things going on...

    - you've said your pump isn't PMW, and has no cabled input other that power. Your controller may well be showing a %age pump speed output, but not sure how that could be getting communicated to the pump. So it's likely just the low output voltage it is trying to transmit.

    - have you heard/noted variations in your pump speed, or is that just based on the controller showing a varying speed output. Many pumps can control their speed, based on const flow or const pressure, or as the I II III selector allows constant speed. That has nothing to do with any feedback as regards temperature (it's to do with varying back pressure in say radiator circuits, as TRV's open/close).

    If you're really stuck with the instructions, and you can't find an electronic version, maybe you could scan the relevant sections (prob just one page) and post on here, for us to take a look.
    • CommentAuthorphiledge
    • CommentTimeFeb 28th 2020
    • CommentAuthorrevor
    • CommentTimeFeb 28th 2020
    Thanks for finding the manual you did well philedeg. Yes that is the system but I have a different tank I have used a Gledhill thermal store rather than the Velux solar tank.

    ( I had to cut and paste the link in case someone else tries to look at it. )

    Can't answer the questions yet GreenPaddy will do some experimentation and observations of the flow meter next time we have some sun. Not noted any pump speed variation the system is very quiet and has a EPS case around it which dampens any noise. I will need opening up to view the flow meter. It is not that very often to run the UFH when sun is shining unless I want to dump heat into the floor to maintain a large temperature differential between the flow and return. I have assumed the hotter the flow and the colder the bottom of the tank is that I should get more heat transferred into the store. I guess there will be an equation somewhere linking temperatures flow rate and size of coil. (Takes me back over 55 yrs ago to calorimetry in physics O level)
    • CommentAuthorGreenPaddy
    • CommentTimeFeb 28th 2020
    No doubt it's me being a diddy, but I can't get the link to work, cut and paste it, even tried typing in "www.sigenergy.co.uk"...seems to be forbidden to me?? What am I doing wrong?
    • CommentTimeFeb 28th 2020
    GreenPaddy asked: "No doubt it's me being a diddy, but I can't get the link to work, cut and paste it, even tried typing in "www.sigenergy.co.uk"...seems to be forbidden to me?? What am I doing wrong?"

    I don't think you're doing anything wrong. I cut-and-pasted originally and looked at the document. Now I get 403 like you. So either the link has been changed or the website has made the document inaccessible.

    Given that a web search turns up the same URL but that also gives 403, I think sigenergy have changed their site for some reason.

    There are different documents that also have a diagram of the pump station at:


    • CommentAuthorphiledge
    • CommentTimeFeb 28th 2020
    Ive just downloaded a fresh copy twice so the link is working for an android tablet ok!!
    • CommentAuthorrevor
    • CommentTimeFeb 28th 2020
    I have just tried it, copy and paste worked in Microsoft edge but not internet explorer. Clicking on it does not work get 403 error in edge. Going via history works also. Using a PC Windows 10.
    The djh links work. The system here is very similar to mine except the pump station is slightly different for the USA market. No pump station manual amongst the info.
    Phil's link is working fine for me on Chrome.

    "The adjustment of the fl ow rate of the thermal
    carrier medium takes place by controlling the speed
    levels (I, II, III) of the circulation pump and the throt-
    tle in the fi ll/drain fitting"

    So the adjustable parameters in the controller help with 9 different configurations of multiple tanks, ufh, woodstove, multiple panels etc, but don't control the pump speed.

    If you are not bothered about collecting very hot water for a shower, then the best strategy maybe to keep the store as cold as possible, as the pump only runs when the panel is warmer than the store. Do this by pumping the heat straight into the ufh as you described, the solar controller isn't involved in this. In summer you may want a different strategy!

    (Edit: the same effect maybe comes cheaper by sun shining through the window into the floor?!)
    • CommentAuthorGreenPaddy
    • CommentTimeFeb 28th 2020
    Excellent, I'm not a diddy, but my laptop is (bad workman always blames...)

    So sounds like no speed control from the controller. Makes it nice and simple. Stick it at III for most of the year. If on some days you want hot water, drop the speed. The UFh should keep the base of the store as cool as you could hope, maybe around 30oC 35oC, so that's not bad for an energy dump from solar.

    On days when the sun doesn't get the panel above 30oC, even when the water is stationary, you aren't missing out on much (unless you go down the Vikinghouse route of 15m2 of panels, or the whole facade of your house).

    On other days, the pump will just cycle, so you'll get most of what's available. The key is having a place in the store that's cool enough for the not so warm (say 40oC water to go). Yesterday's sun took my cylinder up to 60oC, today's snow took it back down.
    • CommentTimeFeb 28th 2020
    The original link is working again for me now, FWIW.
    • CommentAuthorGreenPaddy
    • CommentTimeFeb 29th 2020
    Ok, so I've now opened the document posted by philedge, and here's what I've gleaned from it;

    - it DOES have speed output control for the circ pump (must control power delivery to the pump, prob by voltage regulation)
    - important page 45, section 4.1.8 deltaT regulation
    - set the delta ON "dTO" setting to say 6oC (that's the dT between collector and store-base temps)
    - that brings the pump on at min speed of 30%
    - then there is a next pump speed step up of 10%, activated when the nominal value dT "dTS" is reached
    - there after the pump speed will be increased in steps of 10% for each increase or RISE in the diff temp set in "RIS"

    So for example; set dTO=6; dTF=3; dTS=10; RIS=2

    dT collector to storebase as temp is increasing would give;

    dT= 6oC...switch pump on @30%
    dT=16oC...pump @ 40%
    dT= 18oC...pump @50%
    dT=20oC...pump @ 60%
    dT=22oC...pump @ 70%
    each further 2oC rise in dT adds 10% pump speed up to 100%

    dT = 3oC...switch pump off

    so you have loads of control over roughly how hot the water drawn from the collector will be, as you not only have the variability of the above ranges, but you also have another 2 layers in terms of the pump speed setting on the pump itself. BUT you won't "control" the water actual temp, you'll only control if it's at the hotter or cooler ends of the spectrum for that particular level of solar insolation.

    Taking extremes, if you want higher flow of cooler water, then set pump speed to III, and set the dTS and RIS values low. Conversely if you want very hot water, then set pump speed to I, and dTS and RIS to high values.

    There are so many variables going on, sun, store temp at various levels in the store, what you are needing the water for at that time (heating, DHW), etc, and you must remember that your coil will have a pinch point of maybe 4oC (ie. it won't transfer any energy through the coil until the solar water is 4oC hotter than the store water), losses in the pipes, etc, so setting your dTO/F/S numbers for some perfect energy gain, will be complex, and shifting daily if not hourly.

    Think VERY carefully what you are trying to achieve, then you can set the above. Remember, adding coolish solar to the base of you store will start to reduce the temp of water at the top of your store. You may end up with more "total energy" in your store, but have lost the usefulness of the hot water for DHW at the top of the store. In other words, it is possible to overthink the whole thing.
    • CommentAuthorrevor
    • CommentTimeFeb 29th 2020
    Thank you all. There is a lot there to go through. Starting to make sense now. Will print off these responses so have them handy next to the unit. Many thanks GreenPaddy for making senses of section 4.1.8 clearer for me I just glazed over when I have read it before.The settings are as per factory settings. Have now got a better understanding of how to tweak the system.
    • CommentAuthorphiledge
    • CommentTimeFeb 29th 2020
    Before you go fiddling too much, have a read of page 34 in the second linked manual that DJH linked to. That manual suggests its just ON/OFF control of the pump.

    Probably need to find the model number of your control system and work out which manual is the correct one for your set up.
    • CommentAuthorrevor
    • CommentTimeFeb 29th 2020
    Thanks philedge. This manual is nothing like the one I have. Looks like it is a USA version.The menu is very different and my display does show the different % pump speed. GreenPaddy put his finger on it for me. The manual you found at sigenergy is like mine the page numbers are different but the section numbers are the same. When I get opportunity I will check what the flow rate is at the different % speed indicated.
    • CommentAuthorLF
    • CommentTimeMar 1st 2020
    Are you claiming rhi or did you go DIY route?
    Would you advise a ball park cost?
    How many m2 of solar heaters?
    I am looking at doing this for my hot water and threads on here are all from several years ago.
    • CommentAuthorrevor
    • CommentTimeMar 2nd 2020
    LF No RHI not worth it as cannot legally use the solar hot water to heat underfloor heating. Perverse!
    Did DIY, got roofers to help me get the panels in place whilst putting roof on. 5M2 Approx. cost 2K plus cylinder whatever one you chose with solar coil. You could do it cheaper if you do not buy a branded kit but you won't save much I do not think.

    Mine is vented to avoid pressure regs and is a Gledhill 350 L direct with external heat exchanger for heating DHW on demand. Need to match the sq M panels to the coil size, The cyl manufacturer will state what area of panels is suitable.
    • CommentAuthorphiledge
    • CommentTimeMar 2nd 2020 edited
    Posted By: LFAre you claiming rhi or did you go DIY route?
    Would you advise a ball park cost?
    How many m2 of solar heaters?
    I am looking at doing this for my hot water and threads on here are all from several years ago.

    Have a look on the Navitron web site as everything is specified and priced there- 20 tube system is £1400. How big a system you need depends on HW demand, but I think youll find sizing guidance on the Navitron site
    • CommentAuthorEd Davies
    • CommentTimeMay 9th 2020
    My humble opinion is that it's easy to overthink the flow rate; so long as it's not grossly out it won't matter. If the flow rate is much too low then the flow water from the panels will be too hot so the losses will be greater. Similarly, if the flow rate is too high then energy will be wasted pumping the fluid round unnecessarily quickly. Between those extremes the net rate of heat transfer just won't be very sensitive to the flow rate.

    Essentially, the return temperature to the panels (R) will be set by the temperature of the destination thermal store [¹] plus only a small amount as long as the heat exchanger there isn't too undersized. The temperature of the flow from the panels will then be that plus a few degrees (ΔT) . The average temperature in the panels, which determines the panel losses [²], is R + ½ΔT which will be mostly determined by R rather than ΔT.

    That says to me that thinking strategically about where the energy is to be stored (choosing R) is much more important than diddling with the pump speed. In particular, you only want to heat the smallest possible amount of material to DHW temperatures during times of the year when you're eking out the last available joule.

    Also, heating the hottest parts of the thermal store at the right times of day will matter. Losses are greatest when the temperatures in the panels are highest so you want to heat the hottest parts during the brightest times of the day to keep the duration of that heat loss as short as possible.

    [¹] using “thermal store” quite generally to mean a place where heat is stored, not just a specific type of cylinder.

    [²] approximately: the losses are non-linear with temperature so it's not really just the average temperature which matters but for small temperature differences the average temperature won't be a terrible estimate.
    I agree with Ed. All the tweaking in the world wont make more than a few % difference. These systems are essentially self balancing.
    • CommentAuthorrevor
    • CommentTimeMay 22nd 2020
    Thought I would close the loop on this one. After some monitoring the pump % speed varies by 10 % each step but does not need much change in the differential temp between the top of the store and the bottom. A 20 deg difference equates to 90% pumps speed and 6 deg 30%. A 1 degree temp change can change pump speed by 10% e.g 19 deg differential 80% 20 degree 90%. similar to what Green paddy has expressed earlier. I have left the default settings as they were.
    Changing pump setting from I to II increases the outgoing temperature back to the collector so have kept it at I. The only change I have done to the settings is increase the max store temp from its default setting of 70 to 75 as the panels were topping out at about 150 degrees. May increase to 80 if still topping out but not sure on the wisdom of going this far.
    Since end of February boiler has only been on once in middle of March for 1 hour to heat up for domestic water since then been on solar HW all this time but we have had some exceptional number of hours of sun.
    Many thanks for all your inputs they are much appreciated.
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