Getting Hot in Here

[Spinny]

The other day it was hot in the house and my thermostats were saying 27C. They need calibrating and seem to overdo the actual temperature by a couple of degrees - so I would say it was 25C. However the outside temperature was only 21C.

 

So despite the insulation in the new extension it doesn't seem to keep the house cool in summer.

 

Why is the house getting hotter than outside ?

Is it just the effect of sunlight coming through the glass in the bifolds, window, and 3 rooflights - warming the inside and the insulation keeping this warmth in ?

Is it the slate grey pvc membrane absorbing heat from the sun, and despite having 150mm PIR underneath transferring heat into the extension ?

 

Any thoughts ?

 

(I remember asking my architect about aircon  at the design stage and he poo-pooed it as not necessary or worth it in the UK. Seems a shame there isn't a way to run wet underfloor heating in a way that would cool the floors ?)

[IGP]

Yes sounds like solar gain. Like a greenhouse. 
 

Do you have an ASHP?

[JohnMo]

1 hour ago, Spinny said:

bifolds, window, and 3 rooflights

You won't need much sun to make it super hot.

 

Add blinds/curtains to room lights, window and bifold, and manage temperature by closing as needed. If you an ASHP can it do cooling?

[SteamyTea]

What was the outside air temperature?

What is the air infiltration number?

What orientation is the new extension?

How much glazing as a fraction of insulated wall?

What sort of roof is there.

Does it have 'always on' electricals i.e. home entertainment, fridges, tumble dryers?

 

Below is my house temperatures. for the last month and for last week when it was warmer.  Last week was 1.5°C warmer (mean), the house was 0.8°C warmer.

 

 

 

[Alan Ambrose]

>>> Seems a shame there isn't a way to run wet underfloor heating in a way that would cool the floors ?

 

There’s lots of info here on ‘t ‘ub on running heat pumps in cooling mode. Some do it out of the box, some can be configured, some can’t.

[Spinny]

I attach temp history for Friday from my heatmiser app. The drop in the evening is when we opened the doors because it had become so hot, hence the rapid drop.

 

We have a gas boiler, no heat pump.

Extension is at the rear (37sqm - east facing) and north facing side (3sqm). So we do get sun pouring in through the east facing bifolds (3.5m wide by 2.4m high) from early through to midday. The adjacent window is south facing (1.5m wide by 2.4m high). We have 3 roof lights in the rear extension - 2sqm + 1.6sqm + 1sqm = 4.6sqm total.

We have a 0.5m wide roof overhang to the bifolds and side window.

Construction is 150mm PIR under 120mm concrete slab with heating pipes in. Blockwork cavity walls with render and cladding - 90mm PIR in cavity (cladding to south facing wall). Warm roof with 150mm PIR and slate grey PVC single ply membrane.

The bifolds and window double glazing seem pretty efficient - we regularly had condensation on the outside in winter.

? 

I guess it is 'solar gain' ? Sun shining onto the glass and onto the internal concrete slab ? Temp rising  through the day from early morning.

Presumably the insulation is good enough to stop the heat escaping so we end up hotter than outside and it doesn't cool off much at night either ?

 

[Nickfromwales]

Do the roof lights open? 

[marshian]

One of the best things I have done to manage temps and humidity in the house is to install a PIV unit in the loft - it runs at 20 l/s in winter (1 ACH) and 40 l/s in spring summer and autumn (2 ACH)

 

It has several program modes but I set it to go into standby at 27 Deg C below that temp it constantly runs

 

In summer it runs for approx 10 to 12 hrs as a result of the standby mode

 

It's quite noticeable in the data that it has a cooling effect overnight/early morning and overall it helps to limit the solar gain in the south side of the house.

[Nickfromwales]

@Spinny

 

MVHR or trickle vents and extractors?

[marshian]

It is also noticeable from my data gathering

 

1. how much hotter on average my loft is since I have improved the insulation level from 75mm to 375mm in 80% of the loft (still got 20% to do in Autumn) I've recently added to vents in two of the four gable ends and this has helped a lot

 

2. how much cooler the rooms below the improved insulation are compared to previous years

[Spinny]

One opening rooflight 1.6sqm on a hinge and electric motor.

Extractors and trickle vents: Kitchen will have an extractor over hob on south wall 150mm vent pipe ; Utility will have an extractor 100mm ; 3 Trickle vents downstairs. Building notice predated regs change in 2022 and we have no trickle vents in the bifolds.

I am a bit concerned we may perhaps need more ventilation in the extension - only aesthetic option might be putting something through the wall behind where the fridge-freezer will go. I have the inner blockwork leaf omitted here to accommodate fridge/freezer depth. But would have to cut through cladding. Also struggle with sealing up insulation but then punching holes in it which seems contradictory.

 

TBH ventilation never discussed by architect beyond regs requirements for extractors. Wonder whether a standalone MVHR thing as the utility extractor would help ?

We had a single skin 1980's budget kitchen extension built by prior owner and a lean to conservatory before - ventilation was not on the radar.

 

(We have also put u/floor heating in the hallway and utility - so the suspended floors there now have 70mm PIR between the joists.)

(No blinds up at present other than 'within the glazing' blinds on two glass doors- planning internal roller blinds for bifolds and other windows)

Edited 1 hour ago by Spinny

[JohnMo]

9 minutes ago, Spinny said:

Wonder whether a standalone MVHR thing as the utility extractor would help ?

Good possiblity is no.

 

If you have intermittent fans currently I would consider changing to dMEV, these run continuously at a low level and are silent. In our last house the utility fan didn't come on for the 10 years we were there.

[Spinny]

No extractor fans actually fitted yet. The holes have been core drilled and stuffed with rockwool pending fitting them in the weeks/months ahead.

[Nickfromwales]

11 minutes ago, Spinny said:

No extractor fans actually fitted yet. The holes have been core drilled and stuffed with rockwool pending fitting them in the weeks/months ahead.

Pull the rockwool out on the hot days? 

[JohnMo]

Buy Greenwood CV2 or CV3 dMEV. They are best part of silent, they have smart auto boost on rising humidity levels (so taking a shower for example) and cost pennies a year to run.

 

Then install humidity activated trickle vents in place of the your manual ones. Any trickle vents in wet rooms seal up. Then you will have a simple demand activated ventilation system.