Where to position your themostats?

[joe90]

6 minutes ago, jack said:

Why? Is it a perception that air isn't fresh unless it's cold?

 

Yup, I guess so. ?. It’s the opposite of heating, unless you can feel heat radiating at you it must be cold!

[newhome]

43 minutes ago, jack said:

 

Why? Is it a perception that air isn't fresh unless it's cold?

 

Nope, it's a perception that air isn't fresh unless it's directly obtained from the outside I imagine 

 

[TerryE]

19 minutes ago, newhome said:

Nope, it's a perception that air isn't fresh unless it's directly obtained from the outside

 

I find it strange that people don't seem to understand the difference between recirculating heat and recirculating air.  It's almost as if the incoming air has somehow been contaminated by the exhaust.  I just tell people that the entire air in the house is exchanged every 2 hrs.  That's not quite true because our MVHR at 30% flow does about 10% every 20-25 mins so there will be the odd lingering molecules.   The main point is that the air in the house is a lot fresher overall than no MVHR and an odd window cracked open.

[jack]

22 hours ago, newhome said:

Nope, it's a perception that air isn't fresh unless it's directly obtained from the outside I imagine 

 

Yes, but once it's explained that the air is obtained from outside, all that's left is the perception - or perhaps subconscious suspicion - that the incoming air isn't actually fresh, because the ordinary experience in winter is that air from outside is cold.

[newhome]

Maybe it’s a perception that the current air in the room isn’t ‘fresh’ enough so it’s an attempt to fast track its replacement ?. Dunno, it’s a question for @joe90 to ask his Mrs ?

[Jeremy Harris]

I think it's just that we're conditioned to houses where warmth is associated with muggy air and "fresh" breezes are called that because we are conditioned to thinking of them that way.

 

As a consequence, we subconsciously associate a cool air flow as being "fresh" and a warm air flow as not being fresh.

 

It is something that can be unlearned, though.  Even my wife (who loves keeping windows open) has commented on the bedroom not feeling muggy in the morning, something that was very noticeable in our old house, even with a small fanlight window left open all the time.

 

The other thing she's noticed is that the house is relatively dust-free.  One of the benefits of having a pollen filter on the incoming fresh air supply.

[joe90]

17 minutes ago, JSHarris said:

bedroom not feeling muggy in the morning,

 

In our last temporary house back in Bristol, it had double glazing but no trickle vents and if we forgot to open a window before sleeping we would wake in the night feeling “not right” we put that down in the end to lack of oxygen/excess carbon dioxide. This new house is nothing like that.

[Ed Davies]

1 hour ago, joe90 said:

lack of oxygen/excess carbon dioxide

 

It'd be excess carbon dioxide (or other trace gases) rather than lack of oxygen you'd notice. Two reasons:

 

1) there's quite a lot of oxygen in the air compared with other gases, except nitrogen, so respiration will make a huge proportional increase in CO₂ for a tiny proportional reduction in oxygen (e.g., the human race has increased the proportion of CO₂ in the Earth's atmosphere by forty something percent but only made a barely measurable decrease in the amount of oxygen present) and

 

2) human bodies are very poor at detecting a lack of oxygen anyway; we just didn't evolve the need for it. The feeling of gasping for breath when holding your breath is due to excess CO₂ in the blood and lungs, not lack of oxygen.

 

The second of these is why anoxia on aircraft or up mountains is so insidious; it causes no real sensation other than that you do silly things, fall asleep then die. There are secondary clues like fingernails turning blue but you'll probably miss those because anoxia is interfering with your judgement to start with. It's why they say to put your oxygen mask on first before helping others in an aircraft depressurisation (“pick your favourite”) as otherwise you're likely to not help the other person or yourself while still thinking you're doing OK.

[Jeremy Harris]

For 22 years I had to endure a biennial session in a hypobaric chamber, learning to recognise the insidious effects of hypoxia.  It got better as time went on, as for initial aircrew training and the first couple of refresher sessions they used to still do an explosive decompression to 25,000ft.  That's not at all nice. Someone decided that doing routine explosive decompressions was too risky (it was about the time that the MoD finally decided to follow the H&S@W Act) and so from then on we only did gentle climbs (on oxygen) to 25,000ft, then one by one took our masks off and either did repetitive arithmetic, or towards the end, played video games (good for spotting the loss of colour perception as your blood oxygen concentration drops).  Some of us doing high altitude stuff had to do a short (5 minutes, IIRC) session at 32,000ft, pressure breathing (OK if you can tolerate the bubbles that come out of your nasolacrimal ducts - I found them really distracting).

 

The interesting thing was the wide variation between individuals to the effects of hypoxia.  For me, the loss of peripheral vision was the first thing I noticed, followed pretty quickly by colour perception going.  Others had more extreme effects.  I remember one chap doing a chamber run for the first time who just went berserk about 30 seconds or so after coming off oxygen.  It took two or three of us to hold him down whilst the doc put his mask on and gave him 100%.  Afterwards the chap had no recall of his behaviour, but it had been recorded for later analysis.  He got chopped as being medically unfit to fly because of his extreme response. 

 

 

[TerryE]

On 23/11/2018 at 18:34, JSHarris said:

However, because the slab temperature is limited to about 23 to 24 deg C max, this didn't happen, much to my relief.

 

Jeremy, there is one caveat here. I will just expound this for other readers.  If your circulation temp is 24°C, say and your environment set point is at 20°C the the maximum delta T with you slab at circulation temp is 4°C and so the maximum heat output of the slab is roughly 4 × 75 × 7 W, say 2kW.  If you need more than this -- either because  it is extremely cold outside or you are heating the house after absence, then you wont be able to achieve your set point.  

 

In general ,  I would suggest that people decide on a maximum heat output for their slab and crank the figures to set the maximum temperature accordingly. 

[joe90]

There was someone on another forum who had a well insulated block house with UFH which he ran on an electric radiator element and had it set to one degree (21’) above his required house temp(20’) and he found it self regulated in that if the house was up to temp the stat for the element just turned it off. He has been using this for quite some time and found it worked very well for him. The ultimate kiss solution ?.

[TerryE]

@joe90, as I mentioned in my previous post, the UFH is used to top up the heat in the house, and it has to be hotter that room temperature for this to happen.  At the moment it is pretty mild so we need about 15 kW per day or just over 0.6 kW average which requires our slab surface to be just under 1½°C warmer that the air temp.  When it gets really cold this can go up to 4°C warmer.  Setting the heater to 1°C above target wouldn't work for us so most of the cold months.

 

@Ed Davies, I have pretty much abandoned using the slab temp as a control variable.  It's just too much of a PITA as heating it changes the temperature on a far lower time constant than the overall response of the house.  Step changes like visits (our warm bodies leave the house or extra ones arrive) are hard to control for.  I have switched to using the day-averaged hall temperature.  My overall strategy is still to do the bulk heat input during the E& off-peak, but the spread any residual over day once the slab has dropped below a trigger temperature.   Just a change to some lines of code, so no hardware changes required.   I'll report back when I have some decent stats.