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Heating and cooling: Boiler Size & Thermal Store

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    • CommentAuthorringi
    • CommentTimeApr 21st 2016
     
    Firstly, where can I buy stand-alone weather compensator suitable for a buffer tank from? (Shame boilers don't allow more then one flow temperature sensor input, choosing between them based on CH/DHW mode with an option to turn of the pump for a configurable time when unto temperature.)

    I have looked at the spec sheets for some boilers and there are a little more efficient when modulated down, as the heat exchange is then "oversized" for the output the boiler is giving.

    In a lot of buildings a tpi thermostat is all that is needed, as it will run the boiler for a few minutes out of every 10 minutes when the building is close to the required temperature.
    • CommentAuthorringi
    • CommentTimeApr 21st 2016
     
    => "The maximum unvented cylinder size before G3 is needed is 15 litres. "

    I think the regs are different for unvented buffer tanks (just heated from the boiler), as there is no "auto refilling" after the safety value on the boiler has operated.
    •  
      CommentAuthordjh
    • CommentTimeApr 21st 2016
     
    Posted By: ringiShame boilers don't allow more then one flow temperature sensor input, choosing between them based on CH/DHW mode

    That's exactly what combi boilers do, isn't it?

    Pump overrun timing could be done separately.
    • CommentAuthorringi
    • CommentTimeApr 21st 2016
     
    Posted By: djh
    Posted By: ringiShame boilers don't allow more then one flow temperature sensor input, choosing between them based on CH/DHW mode

    That's exactly what combi boilers do, isn't it?


    Commercial boilers often will take an input from a sensor on an external “low lose header” and have an “logic” input that control if they use this sensor, or the sensor on the flow pipe within the boiler. But commercial boilers have outputs like 80kw!.

    This allows different control logic within the boiler when reheating a DHW tank and running the CH. For example the flow to be set higher when reheating the DHW tank.
  5.  
    JonG, yes the Intergas 24/18 combi with 1 bar cold inlet pressure gives just under 9 litre/min. 0.2 bar will give about 3 l/min.
    • CommentAuthorringi
    • CommentTimeApr 21st 2016
     
    Posted By: Water SystemsJonG, yes the Intergas 24/18 combi with 1 bar cold inlet pressure gives just under 9 litre/min. 0.2 bar will give about 3 l/min.


    Whats the pressure drop with a flow rate of 9 litre/min?
  7.  
    ringi, Whats the pressure drop with a flow rate of 9 litre/min?

    The Intergas installation instructions:
    http://www.ultimatehandyman.org/PDF/Intergas/Intergas-Combi-Compact-HRE-Installation-manual.pdf
    Page 23. A flow resistance graph.

    I think I got that wrong. At 9 litres/min through the heat exchanger it is 1 bar resistance. So, 2 bar inlet pressure will give 1 bar at outlet of the combi at 9 litres/min.

    So, an Intergas 36/30 combi to get 13 litres/min at 35C temp rise, will drop the incoming pressure 1.6 bar.

    I think I have that right. I have about 3 bar coming in so I will be fine using a 36/30.
    The Intergas combi has only 4 moving parts as per the Ferroli. I have not looked at the pressure drop of the Ferroli.
    • CommentAuthorringi
    • CommentTimeApr 21st 2016
     
    My reading of the graph gives the same result, that is VERY high and would stop a shower being used directly on that boiler in lots of UK homes!

    What about set the DHW temperature to max (65c) and put a 5M head pump on (Ă‚ÂŁ200+vat for pump) so giving about 7 l/m so reheating a 200l DWH tank in 30 minutes, and also being able to run one 14 l/m shower "for ever" even when the tank is cold.

    4 showers could run from a full DHW tank for upto 10 minutes before the tank went cold depending how much the water gets mixed up in the tank.

    PLEASE CHECK MY MATHS.


    (But only in a soft water area!)
    • CommentAuthorJonG
    • CommentTimeApr 21st 2016
     
    Intergas can have 2 set point temps as can many boilers now so that circs are compensated and ranged as is HW delivery the IG also allows you to set and time a legionella purge and store at lower temps for the rest of the time.
  10.  
    I have heard good reports on the Ferroli HE combi. Like the Intergas It has only 4 moving parts. They are very quiet when I saw a few working and a smallish case that fits in a cupboard. Stainless steel heat exchangers, etc. I assume it does not knock 1 bar pressure from the DHW. I don't know if it can take hot water at the cold inlet. But I assume it does because other Ferrolis do and it is all made of metal, no plastic, so worth checking if that is what is needed. The 38 kW gives 16 litres/min DHW. Quite impressive for a small box on the wall.

    Everything is accessible from the front, including the pressure vessel. It can be scaled in situ.
  11.  
    I am impressed by the level of knowledge here! I don't think I could realistically get to grips with it though I have a similar issue. That being the case, could anybody point me in the direction of a service that designs a system like this?
  12.  
    The Intergas is quite expensive but the Intergas Rapid is far cheaper but little different from the main Intergas:
    http://sxonline.co.uk/intergas-rapid-32-combi-boiler-erp-73165-p.asp

    The 32Kw delivers 13 litres/min DHW but reduces the water pressure by just over 1.5bar. Quite a drop. These need serious looking at the cold water supply before choosing. If you have 3 bar cold mains pressure the pressure of cold and hot at the shower mixer will be far from a balanced hot & cold supply, probably needing a pressure equalizing valve before the shower mixer, if one is not in the mixer (some have them).

    ComeOnPilgrim, many here have fitted what your needs are. If no reply from them, I will be back to start it off.
  13.  
    @WaterSystems - thanks!
    • CommentAuthorJonG
    • CommentTimeApr 22nd 2016
     
    Have fitted loads of Rapids and have one in my house with Evo and OT, no issue with flow rates and not fitted any balancing valves/prvs on any of the installs to date.

    COP, where are you and what is the project, I am intrigued!
  15.  
    Hi @Jon, project is in Bicester, Oxfordshire. Where are you?
  16.  
    JonG, "Intergas can have 2 set point temps"

    Jon how do they do this? It is not apparent from the manual. The web site mentions nothing of it. I intend to do it by kidding the weather compensator to run to maximum burner when needed, and then back to weather compensator control when needed. So two temperatures but not simultaneously.

    I think an Intergas with a 1.5 bar drop in pressure on DHW on a marginal pressure mains would have problems, while others would not. If you have enough flow and pressure it would make little difference.
    • CommentAuthorJonG
    • CommentTimeApr 24th 2016
     
    COP have you got any more detail on what yo are doing I can check with colleagues and see if anyone can help, we are in Glossop, N Derbyshire but in touch with a network of good installers via FB.

    WS, the IG can provide 2 diff flow temps independently not simultaneously, so usually HW is on a thermistor/sensor and HW priority, temp drops in cyl thermistor calls on the boiler, opens the 3 port valve and ramps to chosen flow set point and chosen power output.

    Once satisfied it reverts to WC heating setpoint and switches the 3 port.
  18.  
    @Jon, it's a timber framed hempcrete new build. We'd like a design that runs as passively as possible, ie with gravity etc, and with minimal maintenance (eg we'd prefer not to have to have the heat store looked at each year). We will have a stove and would like provision for solar in the future when we can afford it. It's 120 m^2.
    • CommentAuthorJonG
    • CommentTimeApr 25th 2016
     
    Thanks COP I will see if I can find anyone to talk to.
  20.  
    JonG, thx, pretty common stuff.
  21.  
    Posted By: JonGHave fitted loads of Rapids and have one in my house

    JonG, how noisey is the Intergas Rapid?
    • CommentAuthorJonG
    • CommentTimeApr 26th 2016
     
    It's not WS, one of the features of IG, who have just won Heating Product of the year.

    The main differences between it and the HRE are as follows:

    EV inside case at front on swing arm
    Centre flue
    Aluminium flue to cater for high temp through centre of the boiler, this does mean the knuckle needs attention every couple of years due to build up from partial neutralisation of the flue condensate
    Case is harder to remove/fit
    Slightly different software, which only seems to affect WC but a patch is on its way
  23.  
    Posted By: JonGIt's not WS, one of the features of IG, who have just won Heating Product of the year.

    The main differences between it and the HRE are as follows:

    EV inside case at front on swing arm
    Centre flue
    Aluminium flue to cater for high temp through centre of the boiler, this does mean the knuckle needs attention every couple of years due to build up from partial neutralisation of the flue condensate
    Case is harder to remove/fit
    Slightly different software, which only seems to affect WC but a patch is on its way

    JohnG thanks.
    Does the flue knuckle need cleaning every two years?
    So a firmware bug in the weather compensation. A serious bug? I assume not fixed yet.
    The HRE was quiet enough, if it is like that well OK. The equiv Ferroli is 'very' quiet.

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