mvhr upgrade

[lizzie]

I am having my heat exchanger changed to an enthalpy one on Tuesday.  I hope it helps as it has been very difficult living in such a dry atmosphere with diy humidifying to try and improve things.

 

I have only ordered the enthalpy unit as with fitting it is coming in at over £1000, the humidistat would be another circa £500 with fitting, so for both of those its almost half as much again as the whole system cost and I cant get the vat back now of course so seeing how I go without stat.

 

Does anyone else have experience of enthalpy and no stat?

 

He is also going to reset the airflow pressures as I am using F7 filters and the book says they need to be reset from defaults for those.  I have taken note of Jeremy saying you should hardly feel the airflow (I can certainly feel it) so does anyone know should I be asking him to do to a different setting than building regs one?  The man coming to do it is not the orginal installer.

 

I am going to ask him to look UFH to see if he can help me get that sorted although he is only booked for MVHR visit so it may mean a return if he can help....start small dont scare them off hopefully!

 

 

 

 

[HerbJ]

We have an enthalpy heat exchanger, which was installed as part of the original installation 2/3 years ago - we have  PAUL Novus MVHR.  We installed the enthalpy HE because we have a relatively large house (340m2), there are only two of us normally living here. and it was recommended that a enthalpy HE would prevent the air getting too dry in this situation.  It has worked well for us

 

We do not have humidistats installed but control boost settings in bathrooms and downstairs cloakroom  are initiated automatically when the lights are switched on in those rooms - the controller allows adjustment of the boost run time after the lights are turned off in those rooms (currently set at 15 minutes). If we require greater ventilation when cooking or drying clothes in the utility room, we simply use the boost setting on the remote controller, which is located outside the kitchen.utility room.

 

As I respond to you, the house is sat at 23 C and 38% humidity on the low settings. Our system was set up with the BR  values set as the 100% setting  and the boost setting at 130% of BR values. We also have a reduced/low settings of 70% BR values, which is what the system usually operates at.  We have remote controller for our MVHR in the hall and it is very easy to change all these values from this controller.   

 

The removal of the standard HE and installation of the new enthalpy HE should only be a 10 minute job, providing your MVHR unit is easily accessible. (our is in a plant room and we could change the HE it in 5 minutes...). There should be no need for any further adjustment of the system. 

 

We also have an F7 Filter on the inlet and  G4 filter on the return.  Again, we do not  change any settings when using an F7 filter.

[lizzie]

Thank you @HerbJ that is great info. Much appreciated. Our unit is in the plant room and easily accessible and I have watched the utube on changing it so hopefully it want take him long....they are being very kind and not charging me the call out fee but just the hourly rate but its a min of an hour at a time so if its an hour and fifteen I have to pay for two hours.  My manual tells me that F7 filters affect the pressure and it will need resetting - it was set for F5 in and g4 out originally I think.  I’m still using g4 for out.  I wish I had some independent control for bathroom boosts I have to boost the whole house to get bathroom boost on.  Not ideal. Mine is controlled from my ipad.

Edited March 9, 2019 by lizzie

[HerbJ]

Hi @lizzie

When our MVHR  system is boosted by turning on a light switch in a bathroom ( or manually selecting the boost setting), the whole house airflow is boosted. This is fairly standard for whole house MVHR systems and it would add a lot of complexity/cost to only boost ventilation to individual rooms.  

 

[ProDave]

I am struggling to understand how an mvhr unit can reduce the humifity inside the house so much unless it has some form of cooling / dehumidifying function.

 

Looking at data from the nearest weather station, outside air humidity here hovers around 70-80%.  In the couple of very cold weeks we had at the end of January when it was -14 at night and not above 0 in the day, it only got down to 50%.  So I am struggling to see how you were getting values of 38% unless the old mvhr was doing some dehumidifying function?

 

As I type this inside humidity is 58% inside almost perfectly mirroring the weather station values that dipped to 56 overnight and is now creeping back above 60.

 

If you were "feeling" the airflow from it, it was running way too fast anyway.

[Mr Punter]

5 minutes ago, ProDave said:

I am struggling to understand how an mvhr unit can reduce the humifity inside the house so much unless it has some form of cooling / dehumidifying function.

 

Looking at data from the nearest weather station, outside air humidity here hovers around 70-80%.  In the couple of very cold weeks we had at the end of January when it was -14 at night and not above 0 in the day, it only got down to 50%.  So I am struggling to see how you were getting values of 38% unless the old mvhr was doing some dehumidifying function?

 

As I type this inside humidity is 58% inside almost perfectly mirroring the weather station values that dipped to 56 overnight and is now creeping back above 60.

 

If you were "feeling" the airflow from it, it was running way too fast anyway.

 

I think it is to do with relative humidity, where when the outside air is colder than inside the RH will decrease when it is warmed by taking the heat from the exhaust air.

[lizzie]

@ProDave I am doing well if I am in early 30’s inside when outside rh is 70-80. It can drop down to mid/upper 20’s if it is v hot or cold outside and rh drops.

 

I am hoping for the sort  of results @HerbJ is getting when new enthalpy unit is in.

 

We are 2000sq ft single storey and two of us living there plus the pooch. I am there most of the time but OH is at work so mostly only me to contribute to humidity in the house.

 

Thanks @HerbJ understand your boost scenario better now.

[Ed Davies]

Rule of thumb: the equilibrium vapour pressure goes up by 7% for every 1 °C increase in temperature (or, equivalently, it doubles for every 10 °C increase in temperature).

 

Suppose outside air at 5 °C and 70% RH is warmed to 20 °C by being brought in via the MVHR and warmed a bit by the internal heating. Its equilibrium vapour pressure is now 1.07**15 = 2.76 times what it was outside so the relative humidity drops from 70% to 70/2.76 = 25.4%. There will be internal source of evaporation so it won't be this low in reality but low 30s is easy to understand.

[ProDave]

So what am I doing differently that we maintain a much higher internal humidity?

 

If the incoming air, and cooling it results in such a low humidity why do I not see that?  There will be humidity added by 3 of us and 1 cat breathing, and showering and cooking will add some. And at this time of year the washing is dried inside so that will add some. But the infernal tumble dryer is a condensing one so that should not add much.

 

My guess is we are under ventilating the house? I have not ballanced the flow rates or even measured them, but the air always feels fresh and free from odours so from a practical point of view it is "correct"

[Ed Davies]

12 minutes ago, ProDave said:

My guess is we are under ventilating the house?

 

Or maybe @lizzie is over ventilating? Clearly she's not needing those ventilation rates to get rid of water vapour so either they're needed to get rid of other gasses or she is over ventilating.

[jack]

We run our MVHR at under half the building regs rate, and we never boost unless we're cooking something smelly. Condensation in the bathrooms clears really quickly.

 

Humidity generally sits at around 50% during winter.

[lizzie]

Interesting stuff @Ed Davies 

 

I have suspected I might be over ventilating so I have had experiments with MVHR set to the lowest rate but after an hour or so the air is not feeling fresh enough so back to normal I go.

 

I dont have a record of the current flow rates they were set by installer and its not written down anywhere. I’ve got the password to get into the system set up now so hope I will be able to see when I log in.

 

 I think resetting the flow rates will help but there is no doubt the house is too dry, even the dog is suffering with itchy skin from very dry air.  I am hanging all my hopes on the enthalpy unit.

 

I have what feels like a dead spot for fresh air in my hall too.  No-one else can pick it up but I think it has a stale air whiff in the mornings. No vents in the hall but its open to the living area and we never shut bedroom doors so should be plenty of airflow through.  Who knows what it is.......my extreme sense of smell can be a blessing and a curse.

 

Some years ago I had  to re-train my breathing as I had developed hyper ventilation syndrome....seems like I might now have a whole house with the same syndrome lol

 

 

[Ed Davies]

Yes, difficult if there are VOCs or whatever which affect you for other reasons.

[HerbJ]

I just checked my Commissioning Report and I have misstated some of the settings iI detailed earlier in this post. So, for clarity:

 

Setting 1 - the reduced/low setting , is set at 53% of the BR flow rates. This is the setting that we set for normal day to day operation with juts two of us in the house.

Setting 2 - is set at the BR flow rates - we use this if we are drying clothes in the utility room or have a house full of family/friends

Setting 3 - the boost flow  rate ,  is at 140% of the BR flow rates and used when using the bathrooms & cloakroom   or when doing some serious cooking in the kitchen, with lots of steam/fumes from pots &  pans.  This is the only setting wen there is any ventilation noise and then only from an extract grill in the family  bathrooms.

 

 

[Gone West]

@lizzie From what you have said I'm sure your MVHR is over ventilating. The RH in our house is always 40% to 50% and we have never used the boost button. Ask your engineer to set it up to use the PH air changes per hour for each room that are on the table I sent you. Maybe having a dog in the house adds another problem. Good luck

[lizzie]

23 minutes ago, HerbJ said:

I just checked my Commissioning Report and I have misstated some of the settings iI detailed earlier in this post. So, for clarity:

 

Setting 1 - the reduced/low setting , is set at 53% of the BR flow rates. This is the setting that we set for normal day to day operation with juts two of us in the house.

Setting 2 - is set at the BR flow rates - we use this if we are drying clothes in the utility room or have a house full of family/friends

Setting 3 - the boost flow  rate ,  is at 140% of the BR flow rates and used when using the bathrooms & cloakroom   or when doing some serious cooking in the kitchen, with lots of steam/fumes from pots &  pans.  This is the only setting wen there is any ventilation noise and then only from an extract grill in the family  bathrooms.

 

 

Thank you

[lizzie]

23 minutes ago, PeterStarck said:

@lizzie From what you have said I'm sure your MVHR is over ventilating. The RH in our house is always 40% to 50% and we have never used the boost button. Ask your engineer to set it up to use the PH air changes per hour for each room that are on the table I sent you. Maybe having a dog in the house adds another problem. Good luck

Thank you, I have the table you sent ready for him.

[jack]

2 hours ago, lizzie said:

I have suspected I might be over ventilating so I have had experiments with MVHR set to the lowest rate but after an hour or so the air is not feeling fresh enough so back to normal I go.

 

Even turning the MVHR off completely for an hour shouldn't leave the air feeling noticeably different in my opinion (and experience - I've tried it). Are you sure you haven't mentally mapped still air to stale air? Perhaps you perceive moving air as being fresh?

Re: humidity, have you tried an ultrasonic humidifier? They can pump out quite a lot of moisture for relatively little energy input.

[Jeremy Harris]

I'd second what @jack has said above, and also suggest trying an ultrasonic humidifier.  I built one a while ago and it really is a very effective way of increasing the humidity.  The only thing to watch is to make sure that it gets fresh, clean water.  Decent ones are around £30, so not that expensive as a way to see if one might improve the RH a bit and make things more comfortable.

 

You might also want to consider getting a CO₂ meter, as a way to see how "fresh" the air is really.  I find that the CO₂ concentration correlates very well with the "freshness" felt in the room air, and anything over around 1000ppm definitely seems to tally with stuffy feeling air.

[Dreadnaught]

Hi @lizzie, I know you are careful about your air quality because of your health condition, so just add to what others have said …

 

"Ultrasonic humidifiers should be cleaned regularly to prevent bacterial contamination from being spread throughout the air."

 

It is from the Wikipedia article here: https://en.wikipedia.org/wiki/Humidifier#Ultrasonic_humidifiers. Worth a quick read.

[newhome]

7 minutes ago, JSHarris said:

You might also want to consider getting a CO₂ meter,

 

I have been thinking about getting one of these. Any recommendations please? 

[Jeremy Harris]

36 minutes ago, newhome said:

 

I have been thinking about getting one of these. Any recommendations please? 

 

I made both of mine, one's built in to the house monitoring system and the other's a portable unit that logs data to a µSD card.  I've loaned the portable one out to a few people - you are welcome to borrow it for while.

 

I've not looked at commercial models at all, but the best type of sensor is fairly expensive, and uses non-dispersive IR.  Because of the cost of the sensors I suspect that decent commercial units may be a bit pricey.  I've just had a quick look around, and it would seem that a reasonable unit might start at around £70 or so: https://www.co2meter.com/collections/indoor-air-quality

[newhome]

Thank you, would love to borrow it. Do you just set it up in different rooms and take a reading? 

[Jeremy Harris]

22 minutes ago, newhome said:

Thank you, would love to borrow it. Do you just set it up in different rooms and take a reading? 

 

No problem, PM me your address and I'll stick it in the post next week.

 

It needs mains power (but has a battery back up for short power cuts) and can be moved from room to room easily enough.  It measures temperature, CO₂ and relative humidity and logs the displayed data (along with date and time) as a .csv file to a µSD  card every 6 minutes.  The files on the µSD  card can be loaded into a spreadsheet programme (LibreOfice Calc, Excel etc) directly, and then used to produce any plots you like.

[lizzie]

1 hour ago, Dreadnaught said:

Hi @lizzie, I know you are careful about your air quality because of your health condition, so just add to what others have said …

 

"Ultrasonic humidifiers should be cleaned regularly to prevent bacterial contamination from being spread throughout the air."

 

It is from the Wikipedia article here: https://en.wikipedia.org/wiki/Humidifier#Ultrasonic_humidifiers. Worth a quick read.

Thanks @Dreadnaught you are right about my health worries and humidifiers.  I bought one of these a few months ago and have used it a bit but the concern over bugs worries me hugely and my consultant has advised me not to use it.  The battle between keeping bug free and keeping lungs in half decent working order with reasonable humidity in house is a tricky one and tbh not one I can seem to win unless I take steps to change the air quality in the house on a permanent basis. I hope the enthalpy unit will help.

 

@jack we feel a difference in the air with mvhr turned right down, its not just me but it may be that it is perception. It is still and maybe that makes if feel stagnant somehow.  I cant tolerate it for very long.

 

 In respect of breathing my body behaves a bit differently to those of you with normal lungs (and I wish I had them!) if you were to try breathing through a straw that is how I am most of the time and sometimes the need for good clean fresh air is overwhelming much like a thirsty man desperately needing a glass of water, its not a conscious thing, at times like this I usually go outside to get air but in bad weather thats not great.  I had hoped good air in the house 24/7 would help overcome this.

 

@JSHarris I have a co2 meter.  The levels are good there is no problem with the air quality in the house we sit just above or below the 400 so its just the lack of humidity which makes the air too dry.

 

The motivation for building this house was for health not money or energy saving.  I spent a long time putting together my wish list for the MVHR...humidity control, anti bacterial pipes etc etc......I wont say who was in charge of getting in the quotes and yes I did question if the system as specced would meet my needs and I was assured it would. If the enthalpy unit does not help then I think I will have to admit failure and go back to old fashioned methods of ventilation to keep humidity at a bearable level.

 

I am keeping everything crossed for Tuesday. Thanks for all your input everyone I really appreciate it.