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MHRV with water or electric post heaters

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  • 23-01-2015 11:19pm
    #1
    cheviot26
    Registered Users Posts: 7 ✭


    Hi does any have experience with MHRV post heaters - which heat the air travelling through the supply ducts.
    I have heard of electric heating elements and hot water being used to heat the air.
    Are there any such products available in Ireland.


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    #2
    Borzoi
    Registered Users Posts: 2,876 ✭✭✭Borzoi


    cheviot26 wrote: »
    Hi does any have experience with MHRV post heaters - which heat the air travelling through the supply ducts.
    I have heard of electric heating elements and hot water being used to heat the air.
    Are there any such products available in Ireland.

    Very common items in the commercial ducting sector, usually hot water or heat pump for heat. Almost never directly electric.

    Absolutely no need for extra heat if your using a heat recovery system


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    #3
    Borzoi
    Registered Users Posts: 2,876 ✭✭✭Borzoi


    cheviot26 wrote: »
    Hi does any have experience with MHRV post heaters - which heat the air travelling through the supply ducts.
    I have heard of electric heating elements and hot water being used to heat the air.
    Are there any such products available in Ireland.

    Very common items in the commercial ducting sector, usually hot water or heat pump for heat. Almost never directly electric.

    Absolutely no need for extra heat if your using a heat recovery system


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    #4
    rampantbunny
    Registered Users Posts: 907 ✭✭✭rampantbunny


    Borzoi wrote: »
    Very common items in the commercial ducting sector, usually hot water or heat pump for heat. Almost never directly electric.

    Absolutely no need for extra heat if your using a heat recovery system

    In a house with a slow response response heating system such as an installation with geothermal/UFH making the most of thermal mass, there's no real option to boost heat quickly. It's a slow steady temp. Nothing wrong with that (I'm installing it in my build).

    But there are times when I can foresee wanting a quicker response or maybe my HP fails in winter and there's no one available to fix for a day or two. In both these situations a post-heater could deliver quick/emergency heat. I feel I need something instead of putting complete faith in my HP installation to always work.

    OP, I'm pricing an MHRV system at the moment. Duct heaters are optional for both pre-heating (frost protection) and I think another of the same heaters can be used for post-heating. In talks with supplier to confirm this and how it's all tied together/controlled but if you're interested PM me a reminder maybe next week and I'll fill you in on what I've learned.


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    #5
    Rabbo
    Registered Users Posts: 637 ✭✭✭Rabbo


    I never really understood why utilising the ventilation ducting for the main central heating system in a new domestic house isn't more popular.

    I know that heat transfer isn't as efficient in an air heating system but when the heat demand is so low in a new house you would think it would make sense. Could the ventilation and heating systems not be combined by installing, say, an air-to-air heatpump onto the MHRV system? There would be significant savings on underfloor heating/rads, etc.


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    #6
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,140 Mod ✭✭✭✭BryanF


    Rabbo wrote: »
    I never really understood why utilising the ventilation ducting for the main central heating system in a new domestic house isn't more popular.
    it isn't popular because the majority of people are two tight to put the money into designing/building a house that would need such little heating that it could be provided by:
    say, an air-to-air heatpump onto the MHRV system? There would be significant savings on underfloor heating/rads, etc.
    I understand this has been done in a passive house

    The other issue here is when you have worked out how to heat your house (from combined Mvhr connected heat pump) how do you heat your water?


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    #7
    galwaytt
    Registered Users Posts: 12,761 ✭✭✭✭galwaytt


    Rabbo wrote: »
    I never really understood why utilising the ventilation ducting for the main central heating system in a new domestic house isn't more popular.

    Well, Galway Corporation built and entire scheme of social housing using air duct heating in the late 70's/early 80's (100's of houses) The houses had no chimneys. Then there was a fuel crisis, solid fuel came into vogue and DoE grant-aided the building of fireplaces and................all the duct heating systems were junked.
    Rabbo wrote: »
    I know that heat transfer isn't as efficient in an air heating system but when the heat demand is so low in a new house you would think it would make sense. Could the ventilation and heating systems not be combined by installing, say, an air-to-air heatpump onto the MHRV system? There would be significant savings on underfloor heating/rads, etc.

    Exactly, in a low-demand house, everything is on the table.

    I've seen one done just like you describe in Clare a few years ago. There was a heating element in the MHRV system heated by water from a buffer tank. The buffer tank was heated by a combination of solar panels and a wood pellet stove w/back boiler (in the sitting room). The only thing stopping people is.......the price of it. (most) people just couldn't justify the cost of it.

    The house has no other form of heating. No rads, no ufh, nothing. House was very very comfy.

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



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    #8
    Rabbo
    Registered Users Posts: 637 ✭✭✭Rabbo


    Interesting. If an air to water heat pump could be combined with an a heat transfer element in the MHRV, it would remove the need for buffer tank & solar array and keep costs down. It would also provide hot water. I suppose the ducting would need additional controls(room by room) than a standard MHRV system but that might be possible with electric valves at the outlet points.

    Maybe there's an opening there for heating system manufacturers to come up with a package


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    #9
    galwaytt
    Registered Users Posts: 12,761 ✭✭✭✭galwaytt


    Rabbo wrote: »
    Interesting. If an air to water heat pump could be combined with an a heat transfer element in the MHRV, it would remove the need for buffer tank & solar array and keep costs down. It would also provide hot water. I suppose the ducting would need additional controls(room by room) than a standard MHRV system but that might be possible with electric valves at the outlet points.

    Maybe there's an opening there for heating system manufacturers to come up with a package

    ....the only thing there imho, is over-complication of controls. I think we need simpler, not more complicated ones tbh.

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



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    #10
    sydthebeat
    Subscribers Posts: 41,083 ✭✭✭✭sydthebeat


    there already are 'air to air' heat pumps on the market


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    #11
    cheviot26
    Registered Users Posts: 7 ✭cheviot26


    Thanks for posts -The house i intend to build has passive standard insulation and air tightness. I am thinking of solar panels and stove with back boiler for hot water -stove will also do space heating down stairs-the problem is to get some method of heating the upstairs bedrooms without being expensive - the system used in the clare house mentioned above which incorporates MHRV seems like an option.
    Its just the extra money being spent on insulation and air tightness should off set the need for an expensive heating system.


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    #12
    Rabbo
    Registered Users Posts: 637 ✭✭✭Rabbo


    You have the right attitude wanting to prioritise insulation and air tightness however I don't think its ideal to depend on a stove as your main space heating system. It not exactly practical to have to light a stove if you find the house cold on early winter mornings. The lack of control would also have a detrimental effect on your BER rating if the stove is considered the primary heating system.


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    #13
    sydthebeat
    Subscribers Posts: 41,083 ✭✭✭✭sydthebeat


    Rabbo wrote: »
    It not exactly practical to have to light a stove if you find the house cold on early winter mornings. .

    its incredibly practical ????

    im not sure what youre getting at here.

    a house built to passive levels with a stove doing space heating will heat up very quickly by just the stove alone.


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    #14
    Rabbo
    Registered Users Posts: 637 ✭✭✭Rabbo


    I wouldn't consider lighting a stove and all that it entails with fuel, ash , etc. as convenient as a central heating system that you can turn on with the flick of a switch or set with thermostats and timers.

    It's fine in the evenings if you are happy to light and maintain fires but you may end up depending on secondary heating if you find the house getting cold at night.


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    #15
    Calahonda52
    Registered Users Posts: 12,228 ✭✭✭✭Calahonda52


    Borzoi wrote: »
    Very common items in the commercial ducting sector, usually hot water or heat pump for heat. Almost never directly electric.

    Absolutely no need for extra heat if your using a heat recovery system

    Can we have the math on the second statement here please?

    “I can’t pay my staff or mortgage with instagram likes”.



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    #16
    Calahonda52
    Registered Users Posts: 12,228 ✭✭✭✭Calahonda52


    Rabbo wrote: »
    You have the right attitude wanting to prioritise insulation and air tightness however I don't think its ideal to depend on a stove as your main space heating system. It not exactly practical to have to light a stove if you find the house cold on early winter mornings. The lack of control would also have a detrimental effect on your BER rating if the stove is considered the primary heating system.
    And it has to be wood burning only AFAIK.

    “I can’t pay my staff or mortgage with instagram likes”.



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    #17
    Calahonda52
    Registered Users Posts: 12,228 ✭✭✭✭Calahonda52


    cheviot26 wrote: »
    Thanks for posts -The house i intend to build has passive standard insulation and air tightness. I am thinking of solar panels and stove with back boiler for hot water -stove will also do space heating down stairs-the problem is to get some method of heating the upstairs bedrooms without being expensive - the system used in the clare house mentioned above which incorporates MHRV seems like an option.
    Its just the extra money being spent on insulation and air tightness should off set the need for an expensive heating system.

    Yes is the answer to ur first question.
    As for the more complex options,
    Eg
    http://www.nilanireland.ie/domestic-solutions/compact-solutions/compact-p/Max heat
    NOT RECOMMENDING BRAND

    For heat input, max input temp is 52 degrees so u may need a TMV if hydraulic heating circuit used.
    Additional insulation required in heated duct down stream of heater.
    Re the stove, it will have to be completely room sealed
    Recirculating fan only in kitchen.
    No gas hob
    No gas fire
    Condensing tumbler drier only
    Transfer gaps in doors

    “I can’t pay my staff or mortgage with instagram likes”.



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    #18
    Borzoi
    Registered Users Posts: 2,876 ✭✭✭Borzoi


    Calahonda52 wrote: »
    Can we have the math on the second statement here please?

    The OP didn't explain that he was trying to do.

    The reason that air ducting systems aren't commonly used for full heating is the low specific heat capacity of air. With a passive or near passive house it might be a possibility.


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    #19
    Borzoi
    Registered Users Posts: 2,876 ✭✭✭Borzoi


    Calahonda52 wrote: »
    Can we have the math on the second statement here please?

    The OP didn't explain that he was trying to do.

    The reason that air ducting systems aren't commonly used for full heating is the low specific heat capacity of air. With a passive or near passive house it might be a possibility.


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    #20
    ShanE90
    Registered Users Posts: 237 ✭✭ShanE90


    There's a Hitachi unit available, an air to air heat pump which tempers the supply air to compensate for the losses across the heat exchanger when heating/cooling. See link

    http://www.hitachiaircon.com/argws/servlet/FileViewer?groupID=1105&langID=1


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    #21
    rampantbunny
    Registered Users Posts: 907 ✭✭✭rampantbunny


    Borzoi wrote: »
    The OP didn't explain that he was trying to do.

    The reason that air ducting systems aren't commonly used for full heating is the low specific heat capacity of air. With a passive or near passive house it might be a possibility.
    Borzoi wrote: »
    The OP didn't explain that he was trying to do.

    The reason that air ducting systems aren't commonly used for full heating is the low specific heat capacity of air. With a passive or near passive house it might be a possibility.

    Have you actually only got 1260 odd posts? :)


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    #22
    Borzoi
    Registered Users Posts: 2,876 ✭✭✭Borzoi


    rampantbunny wrote: »
    Have you actually only got 1260 odd posts? :)
    Stupid interweb on phone :-(


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