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  1.  
    Yes that doesn't surprise me. As an expert in having hot house (26-28 deg C) during the night and 20 deg external air, I purge every night during the summer. It varies for how long but in excess of 12 hours I guess as an average. I achieve (completely guesstimating!) perhaps a single degree avg reduction in house internal temp but that's an important degree! Thing is though I move around 1m3 per second, yes per second, yes m3, and when it is really hot I turn it up to 2.5m3/s. Obviously I have my MVHR turned off and a great big extract fan in the roof! I don't need pipes because it is easily balanced by how open windows and doors are. In fact, surprisingly for me initially, the main advantage of this system is that by choosing the right window one gets lovely cool 20 deg air wafting over our beds all night - mmmmmm nice. (this on a 2 floors totalling nearly 300m2)

    Anyway, the volume of air a MVHR can move on boost is tiny in comparison and as we know MVHR can't be used to move heat around a home, so why should it work any better to move coolth - just another manufacturer's claim, which I imagine cjard you will soon debunk! :smile:
  2.  
    <blockquote><cite>Posted By: Gotanewlife</cite>as we know MVHR can't be used to move heat around a home, so why should it work any better to move coolth</blockquote>

    I had wondered. We've got a roof terrace on top of our house with a big pivoting rooflight. That stayed open a touch for most of last summer with the windows open on 'vent' - a fairly effective chimney effect.
    • CommentAuthorlineweight
    • CommentTimeMay 16th 2017 edited
     
    The claim/aim of this night time purge ventilation is to use the cool air to extract heat from whatever thermal mass exists within the insulated envelope, is that right? Rather than simply swapping a house-full of warm air for a house-full of cooler air?

    The effects could presumably be rather different comparing internally- and externally- insulated buildings.
    •  
      CommentAuthordjh
    • CommentTimeMay 16th 2017
     
    Agreed that MVHR doesn't move a whole lot of heat, or coolth, around but IMHO it's been very important in stabilising the temperature of our house in the summers.
    • CommentAuthorlineweight
    • CommentTimeMay 16th 2017
     
    Something I'm a bit unclear about: with cool air inside, and warm air outside, is an MVHR system able to operate in "reverse" such that the hot air is kept outside and the cool air inside?
    •  
      CommentAuthordjh
    • CommentTimeMay 16th 2017
     
    Posted By: lineweightSomething I'm a bit unclear about: with cool air inside, and warm air outside, is an MVHR system able to operate in "reverse" such that the hot air is kept outside and the cool air inside?

    Yes. If the external temperature is greater than the internal temperature then the summer bypass closes (or stays closed). So the heat exchanger is in circuit and incoming warm air is cooled to (almost) the same temperature as that inside before being circulated. So the best behaviour is to close all the windows, and blinds if you have them, and wait for cooler air in the evening.

    FWIW, our bypass opened again today.
    • CommentAuthorlineweight
    • CommentTimeMay 16th 2017 edited
     
    Posted By: djh
    Posted By: lineweightSomething I'm a bit unclear about: with cool air inside, and warm air outside, is an MVHR system able to operate in "reverse" such that the hot air is kept outside and the cool air inside?

    Yes. If the external temperature is greater than the internal temperature then the summer bypass closes (or stays closed). So the heat exchanger is in circuit and incoming warm air is cooled to (almost) the same temperature as that inside before being circulated. So the best behaviour is to close all the windows, and blinds if you have them, and wait for cooler air in the evening.

    FWIW, our bypass opened again today.


    Have got it now, I guess there are 4 possible scenarios

    1. Comfortable temp inside / colder outside -> heat exchanger works to keep heat in

    2. Uncomfortably warm inside / colder outside -> open bypass

    3. Comfortable temp inside / warmer outside -> heat exchanger works to keep heat out

    4. Uncomfortably cold inside / warmer outside -> open bypass

    Can't think when no. 4 would ever happen though.
    •  
      CommentAuthordjh
    • CommentTimeMay 16th 2017 edited
     
    Posted By: lineweight4. Uncomfortably cold inside / warmer outside -> open bypass

    Can't think when no. 4 would ever happen though.

    Number 4 isn't a condition that opens the bypass on my MVHR, nor on most others I suspect. As you surmise, it's not a condiition that's ever occurred, AFAIK. Opening windows would be the obvious thing to do, much as in the reverse situation to get greater cooling.

    edit: Actually, the condition for #3 is simpler. Whatever the temperature inside is, if it's warmer outside then keep the heat exchanger in circuit.
    • CommentAuthorlineweight
    • CommentTimeMay 16th 2017
     
    Posted By: djh
    Posted By: lineweight4. Uncomfortably cold inside / warmer outside -> open bypass

    Can't think when no. 4 would ever happen though.

    Number 4 isn't a condition that opens the bypass on my MVHR, nor on most others I suspect. As you surmise, it's not a condiition that's ever occurred, AFAIK. Opening windows would be the obvious thing to do, much as in the reverse situation to get greater cooling.

    edit: Actually, the condition for #3 is simpler. Whatever the temperature inside is, if it's warmer outside then keep the heat exchanger in circuit.


    That would be condition 3 if 4 is accepted as impossible, yes.
  3.  
    Posted By: lineweightHave got it now, I guess there are 4 possible scenarios

    1. Comfortable temp inside / colder outside -> heat exchanger works to keep heat in

    2. Uncomfortably warm inside / colder outside -> open bypass

    3. Comfortable temp inside / warmer outside -> heat exchanger works to keep heat out

    4. Uncomfortably cold inside / warmer outside -> open bypass

    Can't think when no. 4 would ever happen though.

    No. 4 happens to our house, we have 50cm stone walls and EWI, quite often this time of year e.g. yesterday ! it was 17deg inside and 24 deg outside. (Daytime temp). So we open the windows. The heating has been off for sometime now!
    • CommentAuthorlineweight
    • CommentTimeMay 17th 2017
     
    Posted By: Peter_in_Hungary
    Posted By: lineweightHave got it now, I guess there are 4 possible scenarios

    1. Comfortable temp inside / colder outside -> heat exchanger works to keep heat in

    2. Uncomfortably warm inside / colder outside -> open bypass

    3. Comfortable temp inside / warmer outside -> heat exchanger works to keep heat out

    4. Uncomfortably cold inside / warmer outside -> open bypass

    Can't think when no. 4 would ever happen though.

    No. 4 happens to our house, we have 50cm stone walls and EWI, quite often this time of year e.g. yesterday ! it was 17deg inside and 24 deg outside. (Daytime temp). So we open the windows. The heating has been off for sometime now!


    How long into summer does your "coolth" store last?

    There must be a bit of a judgement call about whether you want to start throwing it away now, because presumably that means that the effect will not last as long into the "uncomfortably hot outside" portion of summer as it would otherwise.
    • CommentAuthorEd Davies
    • CommentTimeMay 17th 2017
     
    No 4 happens here (NE Scotland) too. Thick stone walls and relatively small windows not well oriented for heat collection later in the day. Already had a day or two this year when it's been a tad cool inside but warmer outside.
    •  
      CommentAuthordjh
    • CommentTimeMay 17th 2017
     
    I was musing earlier - there's a range of external conditions (and probably sequences of conditions) over which my house is comfortable without active heating or cooling. I expect the same is true for all (most?) houses but that the external temperatures for which it is true varies from house to house. It occurred to me that maybe the range is an interesting number, i.e. the difference between the upper and lower external temperatures for which the house is comfortable (or to spec or something). Is the range a figure of merit for the design, perhaps?

    As to where the comfortable range is within the full range of external temperatures, I suppose that as long as the house gets a bit cool at the lower end of the range and a bit warm at the upper end of the range, it doesn't matter too much?

    Sorry if this is OT for the thread.
    • CommentAuthorlineweight
    • CommentTimeMay 17th 2017
     
    Posted By: djhI was musing earlier - there's a range of external conditions (and probably sequences of conditions) over which my house is comfortable without active heating or cooling. I expect the same is true for all (most?) houses but that the external temperatures for which it is true varies from house to house. It occurred to me that maybe the range is an interesting number, i.e. the difference between the upper and lower external temperatures for which the house is comfortable (or to spec or something). Is the range a figure of merit for the design, perhaps?

    As to where the comfortable range is within the full range of external temperatures, I suppose that as long as the house gets a bit cool at the lower end of the range and a bit warm at the upper end of the range, it doesn't matter too much?

    Sorry if this is OT for the thread.


    Sounds virtually impossible to measure though, because external conditions are never static.

    It would also vary quite a lot according to occupancy, activities going on inside, etc.
    •  
      CommentAuthordjh
    • CommentTimeMay 17th 2017
     
    Yes, and there'd be all kinds of disagreement about what the comfortable internal temperature range was and so forth.

    Oh well ...
  4.  
    Posted By: lineweight
    Posted By: Peter_in_Hungary
    Posted By: lineweightHave got it now, I guess there are 4 possible scenarios

    1. Comfortable temp inside / colder outside -> heat exchanger works to keep heat in

    2. Uncomfortably warm inside / colder outside -> open bypass

    3. Comfortable temp inside / warmer outside -> heat exchanger works to keep heat out

    4. Uncomfortably cold inside / warmer outside -> open bypass

    Can't think when no. 4 would ever happen though.

    No. 4 happens to our house, we have 50cm stone walls and EWI, quite often this time of year e.g. yesterday ! it was 17deg inside and 24 deg outside. (Daytime temp). So we open the windows. The heating has been off for sometime now!


    How long into summer does your "coolth" store last?

    There must be a bit of a judgement call about whether you want to start throwing it away now, because presumably that means that the effect will not last as long into the "uncomfortably hot outside" portion of summer as it would otherwise.

    The coolth actually lasts all summer as it is always cooler in the house than outside when the outside is over 25 deg.. We open the windows at night and keep everything shut during the day which helps maintain the coolth. We had the effect before we put on the EWI but it is better now after. i.e. the EWI works both ways, it keeps the heat in or out depending upon the time of year.
  5.  
    What indoor and outdoor temperatures do people have their units at to in this hot weather? I have my unit on 18 degrees for indoor and 13 degrees for outdoor, conditions that are almost permanently meet so the evening bypass is constantly running.
    • CommentAuthorgoodevans
    • CommentTimeJun 19th 2017
     
    Richard, can you run through those settings - it seems to me that the bypass is either a) on day and night or
    b) off day and night.

    you only want the bypass on if its colder outside than inside and it is desirable to have the inside cooler (or occasionally in the spring/autumn if its warmer outside than inside and it is desirable to be warmer inside)
  6.  
    Sorry my question want very clear. My summer bypass is on permanently (good) meeting the conditions of greater than 18 degrees internally and greater than 13 degrees externally.

    My question, which I didn't make clear, was about the 'boost' evening purge coming on. As per the original post there is no 'evening' element to the evening or it just runs whenever the conditions are met. I'm not sure I see the point in the purge running during the day when the conditions would be met, but it might actually be for inside then it. But I'm the evening / a night I do want it to run to cool the house down.
    •  
      CommentAuthordjh
    • CommentTimeJun 19th 2017
     
    My summer bypass was closed today, thankfully, because it was cooler inside than outside.
    • CommentAuthorgoodevans
    • CommentTimeJun 20th 2017
     
    Richard - for best effect you ought to turn off your bypass during the day so that the heat exchanger cools the hot air coming into the building using the cool air being expelled - only when the outside air is cooler than the inside air do you want to bypass (and optionally boost).
  7.  
    Does the Vent Axia know to shut the bypass when it is cooler inside than outside?
    • CommentAuthorgoodevans
    • CommentTimeJun 20th 2017 edited
     
    Posted By: richardelliotDoes the Vent Axia know to shut the bypass when it is cooler inside than outside?

    Reading from the beginning of this post it looks like the Vent Axia uses the 'internal/external temp' settings for this
    If you set internal at 22 and external at say 20...
    the system will bypass/purge if its hotter than 22 inside and colder than 20 outside in all other conditions bypass is closed/cancelled.

    The posts at the beginning of this thread read bypass opens if internal and external temps are greater - but I'm not sure this is correct.

    with your settings at the moment I think you have no bypass until the outside temp is below 13.
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