Moved into a house with an mvhr system need some advice

[mccltd]

I have recently purchased a new house from the bank that was built 3 yrs ago.

mvhr system has been on all the time and I have changed the filters since moving in.

my issue is trying to warm the house.

It’s a vent axia system with summer bypass fitted and a 3 kw inline heating element. 
currently I have the heating element off, and the mvhr is set for an internal temperature of 25 and external of 14 degrees.

Trouble is the vents always seem to be blowing out cool air and the house currently sits around 19-21 degrees. I know I could turn the heating element on but something doesn’t seem right with it always currently blowing cool air.

I’ve  just been in the loft and removed the front panel and pulled out the heat exchange unit. On the left side is a running fan and the houses In take and out put pipes. On the right is a running fan, electric shutter (that’s open) and external intake and out put ducts. Playing round with the settings I can’t switch the electric shutter to close or turn the right fan off.

Does this sound right as with the right fan on and the electric Shuter open it seems to be blowing cold air onto the heat exchanger?

It doesn’t  make any logical sense to me but I’m not an mvhr specialist.

 

thanks for any help/ advice.

 

[JohnMo]

You want summer by pass off.  If it's on the incoming air does not go through the heat exchanger and will just come into the house without being warned by outgoing air.

 

You need both fans on, one is for extract the other for supply air.

 

Hope this helps

[Bonner]

What is the temperature of air coming out of the vents? What is the temperature of the exhaust air going out of the house? Photo of the unit would be useful.

[ProDave]

21 minutes ago, mccltd said:

and the mvhr is set for an internal temperature of 25 and external of 14 degrees.

That sounds like it is MORE than just a simple MVHR unit.  Can you post pictures and / or a model number?

 

How is the house heated?  Ir is the heating element built into this the only heating for the whole house?

 

Usually the mvhr system takes care of ventilation (without wasting heat) and the house is heated by some other means.

[Roundtuit]

As above, how cool is the incoming air?  If your mvhr is 80% efficient, at your current internal temperature (20c), incoming air should be around 16C.

[mccltd]

Hi, thanks for the replies.

the mvhr is a vent axia 443028 with a ventmatika inline heating element.

house only has 2 heated towel rails and an electric heater in the kitchen floor.

the air when I measured it the other day was 20.1 coming out the vents, when I turned the heating element on it went up to 27 degrees but in 3 hours the rooms hadn’t increased by a degree. This is supposed to be a passivehouse design .

 

[ProDave]

If it really is a passive house then 3kW heating for whole house will be plenty.  My house is not a passive house but max heating demand when it is +20 inside and -10 outside is just over 2kW

 

On first heating at such low levels of heat input it will take a long time to heat up the structure of the house, so stick with it, leave it on for 24 hours or until the house warms up.  Thereafter is will not need much heat input to maintain the temperature.

 

[mccltd]

Thanks @ProDave

I'll leave it on for 24 hrs and see what happens.

Also, I will turn off the Summerbypass as @JohnMo suggested.

When should the electric Flaps Close, as so far I've not found a way for it do it automatically so wondering if its working correctly.

The flaps are located in-between the heat exchanger and the fan on the right hand side that has two pipes. both running outside. presumably the intake and exhaust for the system.

[JohnMo]

My flaps work automatically, I cannot select manually (Titon MVHR), but they should only be open when the outside air is warmer than the inside (i.e. summer hot day).  Various other thresholds are set like minimum temperatures, the summer by-pass is installed so as not to heat the house when it not needed or would make things uncomfortable.

[mccltd]

11 minutes ago, JohnMo said:

My flaps work automatically, I cannot select manually (Titon MVHR), but they should only be open when the outside air is warmer than the inside (i.e. summer hot day).  Various other thresholds are set like minimum temperatures, the summer by-pass is installed so as not to heat the house when it not needed or would make things uncomfortable.

Mine were open when i looked and summer bypass was on, but it was definitely colder outside so something doesn't sound right.

[Blooda]

@mccltd We have the same machine [but with no heater]

 

Reference the summer bypass, when you switch the machine on and it go through the start up screens - the 8^th [approx] setting should say "Summer Bypass on" this is not inuitive as it actually means the function to switch the bypass automatically is on, and not particulalry the bypass is on. 

 

If you go into the consumer set up [press down twice] you can set up the choices for the summer bypass.  the 4 choices are:-

 

Off
Normal
Evening Purge
Night time Purge

 

Again these are far from intuitive but there is a good discusion here [goes a bit off topic :)] .

 

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15082

 

But I keep mine at normal.

 

There are no settings in the engineer screens unless you have to change the circuit board.

 

The "indoor temperature" and "out door temperature" are for the automatic activation of the automatic bypass, and as far as I know will not affect the running of the heater. 

 

 

 

 

[Blooda]

On 19/11/2022 at 14:41, Blooda said:

Reference the summer bypass, when you switch the machine on and it go through the start up screens - the 8^th [approx] setting should say "Summer Bypass on" this is not intuitive as it actually means the function to switch the bypass automatically is on, and not particularly the bypass is on. 

 

Just read this again and this first bit is wrong, but I can't edit it.    

[mccltd]

I’m still not sure this is running correctly. I have spoken to vent axia and asked for a company they can recommend to come out and check it.

the first one they recommended didn’t seem to know much about the system so I asked again for a company more technical and 2 weeks on still waiting a reply from the 2nd company they recommended. Do they not have a descent team of technicians in Kent?

[dpmiller]

Bear in mind that the summer bypass is a thermal wax-stat which takes a number of minutes to change state and the stroke of the actuator is only a few mm. I'd opine that if you can "feel" cold air but the house is still 20 degrees-ish the airflow may be a bit high.

 

What % is the airflow at? What size is the house?

 

is the heater bank ONLY controlled by a manual switch?

[mccltd]

with regards to my vent axia it has a variable thermistor located just outside the unit that varies the element temperature.

Currently its set at 29 degrees.

When the heating element is on the air reaches 27 degrees but when off its then blows out 18 degrees so one minute its trying to heat then house then its cooling it.

The unit is turned on and off with a nest thermostat controlling the power to it. So when its below set temperature it turns on element then when it reaches temperate it turns it off causing it to then blow cooler air.

Should I set this thermistor to say 23 degrees and leave it permanently on, I presume it will vary the element temperature depending on the temperature of the incoming air?

[ProDave]

7 minutes ago, mccltd said:

with regards to my vent axia it has a variable thermistor located just outside the unit that varies the element temperature.

Currently its set at 29 degrees.

When the heating element is on the air reaches 27 degrees but when off its then blows out 18 degrees so one minute its trying to heat then house then its cooling it.

That shows the heat recovery is working.  If the heat recovery was not working then the air being blown into the room would be a LOT lower than 18 degrees at the moment due to the very cold weather we have at the moment.

 

The incoming air is never going to be as warm as the house temperature when it is cold, as the heat recovery is not 100% efficient but is sounds like it is quite close so doing the best it can.

 

 

[Temp]

• 4 hours ago, mccltd said:

When the heating element is on the air reaches 27 degrees but when off its then blows out 18 degrees so one minute its trying to heat then house then its cooling it.

 

Yes and no. Mine doesn't have a heater so it's always injecting 16C fresh air. If you didn't have the mvhr system the incoming cold air through trickle vents would be at outside air temperature (-2c where I live just now). That would cool it even more.

 

Does the fan speed change when the heating element is on vs off? I'm not familiar with that model but I would expect the flow rate to be higher when it's heating and reduce when it's just ventilating. I might be wrong about that.

 

If the house isn't getting warm enough my guess is either the fan speed when heating is too low or 3KW isn't quite enough in this cold weather.

 

If the fan speed is too low when heating the air temp might reach 29C turning off the heater before the room temperature reaches its target temperature. Increasing fan flow rate when heating would drop the temperature of the incoming air but increase the amount of energy by allowing the heater to be on for a higher percentage of time.

[mccltd]

1 hour ago, Temp said:

 

 

 

Does the fan speed change when the heating element is on vs off? I'm not familiar with that model but I would expect the flow rate to be higher when it's heating and reduce when it's just ventilating. I might be wrong about that.

 

If the house isn't getting warm enough my guess is either the fan speed when heating is too low or 3KW isn't quite enough in this cold weather.

 

If the fan speed is too low when heating the air temp might reach 29C turning off the heater before the room temperature reaches its target temperature. Increasing fan flow rate when heating would drop the temperature of the incoming air but increase the amount of energy by allowing the heater to be on for a higher percentage of time.

The fan spped doesn't adjust with temperature as the vent axia and ventmatika are not linked in any way. I will try increasing the airflow thou when the heaters on and see if that makes a difiference.