House is overheating

[Savage87]

Hello everyone,

 

It's summer again, yuppy!

It's the second summer with the MVHR which has a summer bypass but the house is still getting to about 27 degrees inside.

 

Does anyone have a solution to cool the house down?

I was looking at integrating something like this but not sure where I would get the lower temperature from?

https://www.bpcventilation.com/cold-water-duct-cooler-range

[Thedreamer]

There is a similar discussion here.

 

New member & MHVR enhancement, upgrade and bypass aftermarket installation - Introduce Yourself - BuildHub.org.uk

[Thorfun]

can you stop the heat getting in? i.e. reduce solar gain

[Savage87]

the problem is partly from the heat gain in the loft there the mvhr is, the intake and exhaust are on the roof. So it's bringing a bit more hotter air. The unit is boxed in and insulated but I'm not sure how much of a difference that is making.

[Thorfun]

so you're suggesting that the MVHR is brining in hot air making the house hot? I would've thought sun streaming through a window would cause a greater increase in internal temperature?

[Savage87]

I'm not sure what's the main cause for the solar gain is, I think there a mix of things but the house is fully insulated. At this stage I'm looking for an air conditioning solution. I understand this might not be the best way to look at a solution for the problem.

[SteamyTea]

32 minutes ago, Savage87 said:

I'm not sure what's the main cause for the solar gain is,

first things first, what has the outside temperature been?

[Savage87]

At about 18:00 outside temp in the shade was about 24 and temp inside was 27, temp in loft is about 30 degrees

[gc100]

My house gets fairly warm/hot , it’s well insulated, airtight, triple glazed, painted black and has an anthracite zinc roof!. Lots of glazing. I knew it was going to get hot in the summer - having lived 20 years in the south of France I find the house at 24 quite comfortable. However I did install AC unit above the en-suite and it’s piped into the master and office both of which are south facing . 
All the gain is pretty much solar I think. My MVHR has night cooling but I don’t think it makes much of a difference as it’s the surfaces which heat up during the day that radiates heat later on. I’ve not used the AC yet as it not hot enough to bother me, having the windows open is just right at the moment.

 

If the gains get too much I wont install solar films on the south facing windows as I get loads of free heat from them in the winter on a bright day.  My most likely route would be a brise soleil slates made of wood over the south windows that I would only have up for summer (single story). I have 2x6 joist behind the cladding above all windows to attach something if I want I the future.

 

this sort of thing

 

 

However I suspect I’ll only go down this route if global warming continues at it’s current rate and the weather gets more extreme (which it probably will). (I have a 6k solar array going in to power the AC by the way…!) 

 

 

 

[SteamyTea]

18 minutes ago, Savage87 said:

At about 18:00 outside temp in the shade was about 24 and temp inside was 27, temp in loft is about 30 degrees

I suspect that the outside air temperature is so high that without active cooling you are going to struggle.

My house, when there is no heating on, is usually about 3°C higher than the outside temperature during the winter.  During the summer is is usually cooler than the outside air (though 24°C would be a treat down here).

So I suspect you are getting incidental gains i.e. cooking, washing, entertainment systems and people, plus if your MVHR is not well insulated, that is heating up in the loft.

[Savage87]

Side tracking a bit, does anyone know if you can install a split aircon unit and the outside unit to be fitted in the loft ?! ?

[Mr Punter]

50 minutes ago, Savage87 said:

Side tracking a bit, does anyone know if you can install a split aircon unit and the outside unit to be fitted in the loft ?! ?

 

It is not ideal and may be noisy in the rooms below.  The outside unit spits out hot air via fan, compressor and condenser.  You may need the loft to be extra ventilated.

[tonyshouse]

Switch off ventilation system. Hang dust sheets over windows, don’t let the sun in , if it works use external shutters, 

 

Does design have large areas of south or west facing glass? Did you get a building physics model? 
 

 

[Savage87]

@tonyshouse the house in question was built in 1910 and it's a mid terrace house, I'll have to check if it got a building physics model ? Jokes.

I'll have to think about putting the MVHR to sleep, it's not going to be an easy decision.. ?

[Olf]

32 minutes ago, Savage87 said:

I'll have to think about putting the MVHR to sleep, it's not going to be an easy decision..

Why not?

As temperatures inside and outside get equal, heat recovery part gets less and less significant and the ventilation can be achieved by simply opening windows.

If the intake is above sunlit surface of the roof, locally the air can get pretty hot so if you sick this in using MVHR is against you. Plus any gains through the attic (which does get very hot).

As mentioned before, your best strategy is to reduce unwanted gains first and then fight the rest with aircon.

[Dudda]

If you can get temperature sensors put into the four ducts at the MVHR unit it will give you a great indication of how it's working. It will show the following:

• Incoming air temperature (what it actually is outside)
• Air exhaust to outside (the temperature the air leaving the house is)
• Supply air temperature to rooms (if summer bypass is on and this is higher than incoming air temp it suggests the attic is warming the air)
• Extract air from rooms to MVHR unit (this will give an indication of the internal heat gains)

I'd use this as a starting point. Other people have done this but you don't have to go to the level of technicality they've done in this thread 

 

[SteamyTea]

3 hours ago, Dudda said:

Other people have done this but you don't have to go to the level of technicality they've done in this thread 

A few of us have code that can run a simple temperature and RH data logger.

£30 will get all the parts you need.

 

 

Here is some very basic code for a RPi, it created daily, time stamped files.

 

 

#!/usr/bin/python

#imports necessary libaries
import os, time, datetime

#load drivers
os.system('modprobe w1-gpio')
os.system('modprobe w1-therm')

while True:
#Sort out the time format
    dt = datetime.datetime.now()
    runday = dt.day
    dt.day == runday

#sensor 1
    tfile = open("/sys/bus/w1/devices/28-0306979462ca/w1_slave")
    text1 = tfile.read()
    tfile.close()
    temperature_data1 = text1.split()[-1]
    temperature1 = float(temperature_data1[2:])
    temperature1 = temperature1 / 1000

#sensor 2
    tfile = open("/sys/bus/w1/devices/28-031097946bbc/w1_slave")
    text2 = tfile.read()
    tfile.close()
    temperature_data2 = text2.split()[-1]
    temperature2 = float(temperature_data2[2:])
    temperature2 = temperature2 / 1000

#sensor 3
    tfile = open("/sys/bus/w1/devices/28-030197941c13/w1_slave")
    text3 = tfile.read()
    tfile.close()
    temperature_data3 = text3.split()[-1]
    temperature3 = float(temperature_data3[2:])
    temperature3 = temperature3 / 1000

#sensor 4
    tfile = open("/sys/bus/w1/devices/28-03149794263a/w1_slave")
    text4 = tfile.read()
    tfile.close()
    temperature_data4 = text4.split()[-1]
    temperature4 = float(temperature_data4[2:])
    temperature4 = temperature4 / 1000

#opens and reads the time
    ts = time.time()

#sets time to UTC and dd/mm/yyyy hh:mm:ss format
    UTC = datetime.datetime.utcfromtimestamp(ts).strftime('%d/%m/%Y %H:%M:%S')

    logfile = '/home/pi/monitoring/data/1wire-%s-%s-%s.csv' % (dt.day, dt.month, dt.year)

#creates and opens or appends data to file
    tfile = open(logfile, "a")

#writes to data file
    tfile.write("%s"%UTC + ",%s"%temperature1 + ",%s"%temperature2 + ",%s"%temperature3 + ",%s"%temperature4 + '\n')

#closes data file
    tfile.close

#sleeps for (n) seconds until next reading
    time.sleep(25)

[Savage87]

Thanks @Dudda/@SteamyTea !

I already have bluetooth temp sensors dotted around the house and in the loft, these are connected to and ESp32(EspHome) and I do all my data logging through Home Assistant and InfuxDB/Grafana.

 

I was hoping to find a solution to run some cool air in the supply distribution box, I'm not looking to cool the house significantly, just to lower the temperature down by a couple of degrees when the house overheats and like I said in my first post, I was looking at one of those heating/cooling coil boxes. If i wanted to heat the air I would have connected it to the boiler, but If want to cool the coil I'm not sure how to get the lower temperature.

[SteamyTea]

4 hours ago, Savage87 said:

but If want to cool the coil I'm not sure how to get the lower temperature.

If you do not have a reversible heat pump you will need to buy a small Air2Air heat pump and somehow plumb it into the air ducts of the MVHR.

You can get cheap A2A for a few hundred quid and they can also heat the place up.

https://www.ebay.co.uk/itm/323974879488

[Savage87]

I was looking at one of those split air con units, I would have liked to fit the whole thing in the loft, but after doing a bit of research, it's a bit tricky to install it ithe loft.

I'll keep on looking...

Another thing that I thought about was to some how use the componets from an small old fridge/freezer to get the cooler temperature. Crazy right?

[SteamyTea]

6 minutes ago, Savage87 said:

Crazy right

I thought the same until someone pointed out that they are fairly low powered.

 

[Russdl]

I though I’d just add a bit to this overheating thread.
 

We’ve been having to cool the house down for the last 24hrs as last weeks blip of mild temperatures (high teens Celsius) had us hitting 23-24 degrees in the bedrooms. 
 

The house is passive standard with external blinds on all bar one of the east and south facing windows and this last summer - fleeting as it was - didn’t cause any greater problem than we’ve just experienced. 
 

Two things caused it I think. The first was as summer started slipping away we started opening the blinds when it was sunny to get the solar gain, we perhaps went too early on that (it’s our first year in the house) so next time round we’ll let the internal temperature dip a little lower before we start inviting solar gain in. 
 

The second element, and this is a complete guess, is the black timber composite cladding on the gable end where the MVHR intake/exhaust are. The gable end is facing just south of east and it gets warm pretty quickly when the sun decides to show and it looks like this is boosting our intake temperature by several degrees. As an example, at the moment it is 11 degrees outside but the intake air is arriving at the MVHR at 15 degrees (from intake grill to MVHR is about 2.0m)
 

I’ve had the bypass open for 24hrs but still the supply air to the house is 1.5 degrees hotter than the intake air, I guess it’s gaining the temperature from the MVHR and ducting despite the bypass being open. 
 

The house temperature is slowly falling towards 21 degrees.

 

I never expected to be having to cool the house in late October. I’m quite delighted to be honest.  

[SteamyTea]

1 hour ago, Russdl said:

The first was as summer started slipping away we started opening the blinds when it was sunny to get the solar gain, we perhaps went too early on that (it’s our first year in the house) so next time round we’ll let the internal temperature dip a little lower before we start inviting solar gain in. 

My two points.

The sun is at a lower altitude in the sky, you you may be getting in more radiation that you think.  More than 'summer', which is generally cloudy and wet where I am.

 

How much daylight do people actually need in a house.  Like artificial lighting, most people put in a lot more than, in my opinion, is comfortable.  But I have had my cataracts replaced with shiny bright acrylic lenses.

[Conor]

Yep, angle of the sun. Low angle means more is bypassing shading by reveals and overhangs and directly hitting surfaces of your interior.

[SteamyTea]

4 minutes ago, Conor said:

Yep, angle of the sun. Low angle means more is bypassing shading by reveals and overhangs and directly hitting surfaces of your interior.

And less reflection off the panes, and less absorption by the panes.

Edited October 21, 2021 by SteamyTea