Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




  1.  
    We have an ESBE VTD300 solar divert valve installed with a large 2-part heat store.

    At present, the incoming solar runs into the top and then the bottom of the tank by default. However, when the incoming hot water reaches 60º, the ESBE valve diverts it through the bottom of the tank only.

    Problem is, there seem to be two thermostats linked to the controller. The controller seems to use the lower thermostat to decide when to circulate the incoming solar. This means that the incoming water is being circulated through the top when it's below the temperature of the top section - thereby cooling it down and also undoing the stratification of the heat store.

    Is this the way it's supposed to work? Seems a bit strange to me.
    • CommentAuthorowlman
    • CommentTimeApr 11th 2019
     
    Has the controller simply been wired incorrectly ?, and can't you change the stat wires round.
    or;
    if the stats are in pockets then switch them.
    • CommentAuthorborpin
    • CommentTimeApr 11th 2019
     
    Doesn't sound right. You mention thermostat and controller, that model of valve is mechanical. The controller seems to be doing the right thing - circulate when the solar is warmer than the coldest part of the tank (usually the bottom).

    Mixer valves can be a pain to get your head around.

    The aim is to get a mixed output of a minimum temperature. So if the mixed output is less than the set point, Hot is open, as the temperature rises, the valve then closes the hot side and opens the cold to 'cool' the mixed.

    The solar supply pipe splits before the valve but eventually is connected to the hot and cold inlet. When below set temp, flow is through one leg of the split and when over, through the other leg which is usually though a heat exchanger in the tank.

    The disadvantage of this is that if the top of the tank is cold and the incoming solar is below the set point, you can end up with a hot bottom and colder top of tank. Pretty rare though I'd think.

    It seems to me the Hot and Cold are the wrong way round. Output from the top of the tank should be Cold and the direct flow from the Solar, Hot (which I know seems backwards!).

    I've attached a diagram which is the best I found.

    My plumber got the valves installed incorrectly the first time.
    • CommentAuthorborpin
    • CommentTimeApr 11th 2019
     
  2.  
    I've just found this on the internet.
      Screenshot_20190411-221417~2.png
  3.  
    This seems to suggest that the valve should be on the return side. At the moment it's on the flow side.
  4.  
    Here's another one received this morning from the valve manufacturer.
      image001.png
    • CommentAuthorborpin
    • CommentTimeApr 12th 2019 edited
     
    .
  5.  
    It seems to me that there are two possible arrangements. The top arrangement circulates through the top OR the bottom, which I could see would be useful during the shoulder season (as all the heat would be concentrated in the top section until it reached 60°).

    The bottom arrangement probably gets more heat out overall when there is plenty of sun.

    However, it seems to me that the ideal arrangement would be: 1. Circulate to the top only until it reaches 60°. 2. Then circulate to the bottom only until it reaches 60°. 3. Then circulate through both coils. I may be wrong though.
  6.  
    Thanks @borpin. Our comments overlapped! I'm assuming that the hot flow to the valve is the white arrow.
    • CommentAuthorborpin
    • CommentTimeApr 12th 2019 edited
     
    I tell you, these valves mess with your brain.

    I'm mistaken in what I said above - that referred to a mixing valve, this is a diverting valve.

    One question, is the pipework as per your 'Solar with 2 stage storage' diagram (i.e. just feeds either coil never both)?

    I think the reason for the setup in that diagram is so that, as the temperature starts to drop in the feed, the controller will probably switch off quicker than in the Avkaterm example I posted. With the second diagram, you can end up with a situation where the top of the tank is over the set point but the feed is below that. The bottom of the tank is still below the feed temperature so the pump continues to run. In that case, the feed is actually being warmed by the top coil and transferring the heat to the bottom of the tank. The only thing to stop that is if the controller takes into account the temperature of the top as well and stops the circulation.

    If your HW is done from the top of the tank, then that is disadvantageous.

    I think your system is working as designed and the 2 designs have different benefits and downsides.

    Mechanical valves are a crude way of controlling wet solar, but reliable. I have moved to a position that diverting PV to an immersion is a better means than wet solar.
  7.  
    I totally agree @borpin, it's not intuitive at all! It's driving me crazy.

    It looks like our pipe setup is like that in the lower diagram from the valve manufacturer. BUT the valve is the wrong way round (it diverts through both loops when warm (<60º), then only through the bottom loop when hot (>60º)).

    However, it looks like our difference controller only has a default set up as in the higher diagram (labelled 11, with two separate loops).
    •  
      CommentAuthordjh
    • CommentTimeApr 12th 2019
     
    Posted By: ComeOnPilgrimIt looks like our pipe setup is like that in the lower diagram from the valve manufacturer. BUT the valve is the wrong way round (it diverts through both loops when warm (<60º), then only through the bottom loop when hot (>60º)).

    What do you actually want to happen? What is the point of the diverter?

    I would imagine that you might want to restrict circulation to the upper coil if there is only limited heat available, and circulate through the top coil followed by the bottom coil if there is plenty of heat. I don't understand the point of the manufacturer's suggested arrangement.

    Circulation should be turned on iff the water in the panel(s) is hotter than that in the tank. Things get tricky in low power cases if the water in the top of the tank is warmer than the water in the panel(s), which is warmer than the water in the bottom of the tank, for example. But I guess optimising edge cases is probably hardly worth the effort.
  8.  
    It's tricky when I don't know the rationale for the different arrangements. My feeling is that it would be best to heat the top only to 60°, then the bottom only. That would seem more efficient than sending the heat through both coils.
    • CommentAuthorphiledge
    • CommentTimeApr 13th 2019
     
    As I see it, youll maximise heat recovery from the solar fluid by passing the solar fluid through both coils. Passing cooler fluid into the collector will give better heat transfer from the collector to the fluid. The downside is it will take longer to get the top of the tank up to a useable temp than if you used only the top coil.
  9.  
    Yes, I guess it's a trade-off. I think I'm going to switch to independent storage for a while to see how it works.
    • CommentAuthorowlman
    • CommentTimeApr 15th 2019
     
    Posted By: ComeOnPilgrimIt's tricky when I don't know the rationale for the different arrangements. My feeling is that it would be best to heat the top only to 60°, then the bottom only. That would seem more efficient than sending the heat through both coils.


    And why can't you do that?
  10.  
    Posted By: owlman
    Posted By: ComeOnPilgrimIt's tricky when I don't know the rationale for the different arrangements. My feeling is that it would be best to heat the top only to 60°, then the bottom only. That would seem more efficient than sending the heat through both coils.


    And why can't you do that?

    I think I could do that, but I would need to change the arrangement of the valves, and I don't want to do that until I am sure I've got it right this time.
  11.  
    As an update, the difference controller manufacturers have pointed out to me that setup 11 requires a relay to control the diversion of the solar water to the top or bottom. I've asked what the logic is, as it might be possible to achieve the same result with the current valve that switches at 60º.

    The only problem would be if the electrical relay switches back and forth at different temperatures, ie, it first heats the top to 60º, then the bottom to 60º, then switches back and heats the top only again. A manual solution couldn't do that.
    • CommentAuthorGreenPaddy
    • CommentTimeApr 16th 2019
     
    Hi CoP, here's how I design and install these...

    - what I'm trying to achieve is that the hottest solar water goes to the top, but when it's cooler it goes to the bottom.
    - this obviously reduces de-strat of the TS not just by putting hottest to the top, but also by stopping hot going to the bottom.
    - leave your solar differential controller to do what it is simply designed to do, ie. compare the collector to the base of the TS. That will bring on the solar pump at say the 7oC diff, and then the ESBE will do its thing and select where the water will be directed.

    The manufacturer states..

    " When the incoming fluid temperature is below the nominal diverting temperature it is diverted to the B port, when the incoming fluid temperature is above the nominal diverting temperature it is diverted to the A port."

    So for the objective, you want;

    - water coming from the collector to be connected to the port that IS NOT "A" or "B".
    - top coil connected to "A".
    - bottom coil connected to "B".

    You have to guess a bit in terms of what temp to set the divert, but that depends on how hot you tend to keep the TS during the day. Lets say you have a gas boiler set to keep your TS at 55oC at the top, then you wouldn't want any solar going to the top that was less than say 60oC. So that's your divert set temp. You might reduce it in summer, if you reduce your gas boiler (other heat source) control temp, so letting the solar do more work.

    Hope that might be of some help.
    • CommentAuthorborpin
    • CommentTimeApr 16th 2019
     
    Posted By: GreenPaddy" When the incoming fluid temperature is below the nominal diverting temperature it is diverted to the B port, when the incoming fluid temperature is above the nominal diverting temperature it is diverted to the A port."


    The risk is that, at the end of the day, as the flow cools down and before it gets below the set point, it can actually cool down the top of the tank.
  12.  
    Here's what the difference controller manufacturer has said:
    'the functionality of a termic valve like the one from Esbe is that it adjusts the flow around the set temperature point.

    For the 60° setting that means below 56°C you would only load section "B", between 56°C-64°C both sections and above 64°C only load section "A".



    Our hydraulic scheme 11 has a different section loading logic.

    We assign priorities to the different storage sections. Lets assume the upper section "A" gets the higher priority 1 and the lower section "B" gets the priority 2.

    This would mean, that the upper section would get priority over the lower section of a storage tank.

    Then lets assume the priority loading temperature is 60°C.


    Below the priority temperature of 60°C the controller only allows loading of the storage section with the higher priority, in this case section "A".

    Even in the case that it would be possible to charge section "B" but not section "A", section "B" will not be loaded.

    Above the priority temperature of 60° we will load section "A" until the switch-off conditions of the section are met (it´s not possible to charge it anymore) and then load section "B" afterwards.



    The rationale behind this is that we want the solar collector temperature to rise, so that charging of the higher priority section becomes possible. This means that the higher priority tank will always be loaded first. This way we increase the availability of hot water in the upper storage instead of loading the whole tank up to a medium temperature.'
  13.  
    Posted By: GreenPaddyHi CoP, here's how I design and install these...

    - what I'm trying to achieve is that the hottest solar water goes to the top, but when it's cooler it goes to the bottom.
    - this obviously reduces de-strat of the TS not just by putting hottest to the top, but also by stopping hot going to the bottom.
    - leave your solar differential controller to do what it is simply designed to do, ie. compare the collector to the base of the TS. That will bring on the solar pump at say the 7oC diff, and then the ESBE will do its thing and select where the water will be directed.

    The manufacturer states..

    " When the incoming fluid temperature is below the nominal diverting temperature it is diverted to the B port, when the incoming fluid temperature is above the nominal diverting temperature it is diverted to the A port."

    So for the objective, you want;

    - water coming from the collector to be connected to the port that IS NOT "A" or "B".
    - top coil connected to "A".
    - bottom coil connected to "B".

    You have to guess a bit in terms of what temp to set the divert, but that depends on how hot you tend to keep the TS during the day. Lets say you have a gas boiler set to keep your TS at 55oC at the top, then you wouldn't want any solar going to the top that was less than say 60oC. So that's your divert set temp. You might reduce it in summer, if you reduce your gas boiler (other heat source) control temp, so letting the solar do more work.

    Hope that might be of some help.

    Thanks @greenpaddy. The problem is that your system ensures high efficiency, but in the shoulder season it may mean that the whole tank is warm, but not hot enough to shower without additional heat. We don't have gas, only an immersion, but that's expensive. Better to divert to the top only until it reaches 60°, at least in the shoulder season.
  14.  
    Commenting on the manufacturer's system, I doubt it's very effective above 60° as efficiency gets less at higher temperatures. Rather than heating the top section to the maximum, it would seem more sensible to cycle between the sections, heating each up in turn by, say, 5°.
  15.  
    Is the valve in question worth the cost and complication?

    Surely if the coils were connected in series and the panels connected top inflow and bottom return the tank would be heated top to bottom as per a normal indirect tank.

    I presume there is a differential thermostat somewhere to stop flow when the panels are lower temp. than the tank.

    Is any advantage of this setup quantifiable?
    • CommentAuthorowlman
    • CommentTimeApr 17th 2019
     
    Peter_in_Hungary ++1.

    Three way motorised diverters are used all the time on a standard single coil cylinder, solar thermal set up. My Resol ST controller has that facility although I don't use it. They are commonly used to divert the the solar liquid to a heat sink/dump radiator when the cylinder is up to temp. Maybe I'm missing something but this valve doesn't seem to be anything different.
    so....
    Do as Peter suggests or use the bottom,/second coil in a similar fashion as a "heat sink rad", and divert to it when the top if the tank is up to temp, I can't see a problem, but like I say I may be missing something.
    • CommentAuthorGreenPaddy
    • CommentTimeApr 17th 2019
     
    I understood your valve to be a purely mechanical valve, acting on the temperature of water passing through it. I don't see how your diff controller has any influence over this valve?

    I can only assume you have additional motorised valves that prevent water going to one coil or another, in addition to the ESBE trying to divert?

    Granted, I don't have drawings, or the detail knowledge of your system that you have, so please accept I'm trying to help, and not be a know it all, but it feels excessively complex.

    The periods in spring/autumn when you'll get any volume of hot water over 60oC have to be very low. Yes, the panel may show 60oC, but within a few seconds of the pump running, it will drop drastically. I'd suggest this will end up with you missing out on lots of low grade energy say 40oC, in an effort to grab some 60oC stuff. That low grade at the base of the TS will still of course pre-heat the DHW as it rises through the coil. Of course it's the top of the TS that trims the DHW output temp, but that 60oC bit at the top will last longer due to the pre-warming at the base.

    If you really want the solar to only the the top of the TS at certain times of the year, then the diff controller needs to change its comparison/reference point from the bottom of the TS to the top. Can it do that automatically? You can certainly do that manually, either by changing the ref point in the settings, or by moving the temp sensor from the bottom pocket to the top.
    •  
      CommentAuthordjh
    • CommentTimeApr 17th 2019
     
    Posted By: Peter_in_HungaryIs any advantage of this setup quantifiable?

    I think this is the key question. How much energy (or dollars) will be saved by each of the possible schemes?

    I suspect anything more complicated than feeding solar-heated water to the entire tank when it is available and topping up the top of the tank to the minimum acceptable temperature with the immersion when necessary won't be energy/cost effective.
  16.  
    Posted By: GreenPaddyI understood your valve to be a purely mechanical valve, acting on the temperature of water passing through it. I don't see how your diff controller has any influence over this valve?

    I can only assume you have additional motorised valves that prevent water going to one coil or another, in addition to the ESBE trying to divert?

    Granted, I don't have drawings, or the detail knowledge of your system that you have, so please accept I'm trying to help, and not be a know it all, but it feels excessively complex.

    The periods in spring/autumn when you'll get any volume of hot water over 60oC have to be very low. Yes, the panel may show 60oC, but within a few seconds of the pump running, it will drop drastically. I'd suggest this will end up with you missing out on lots of low grade energy say 40oC, in an effort to grab some 60oC stuff. That low grade at the base of the TS will still of course pre-heat the DHW as it rises through the coil. Of course it's the top of the TS that trims the DHW output temp, but that 60oC bit at the top will last longer due to the pre-warming at the base.

    If you really want the solar to only the the top of the TS at certain times of the year, then the diff controller needs to change its comparison/reference point from the bottom of the TS to the top. Can it do that automatically? You can certainly do that manually, either by changing the ref point in the settings, or by moving the temp sensor from the bottom pocket to the top.


    Yes, the ESBE is only manual, whereas the difference controller can control an actuator to switch between sections in a very sophisticated way. We don't have an actuator yet though.

    I agree with you, it's a difficult choice whether we try and get a smaller amount of 60° water, or a larger degree of cooler water.

    As @djh points out, really I need to find out how to calculate. I'd be really interested to know how efficiency drops with increased storage temperature. There must be a fairly straightforward calculation (famous last words...).
    •  
      CommentAuthordjh
    • CommentTimeApr 20th 2019
     
    Posted By: ComeOnPilgrimAs @djh points out, really I need to find out how to calculate. I'd be really interested to know how efficiency drops with increased storage temperature. There must be a fairly straightforward calculation (famous last words...).

    I think using a linear model is good enough. The reality probably isn't linear, but it'll be close enough for practical purposes. It's easy to improve the coefficient though, just add some more insulation to the tank.

    In my case I don't care too much about the ultimate efficiency because what heats the tank hottest is the sun. If I'm paying for the electricity, then I don't heat the whole tank and I don't heat it as hot. But that heat does come reliably every day when I ask for it. In the shoulder season the sun preheats the tank to some degree and so reduces the amount I have to pay for.
Add your comments

    Username Password
  • Format comments as
 
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press