21

Technology / Re: Why is a roomstat needed even if every radiation has a thermostatic valve (TRV)?

« on: 27/05/2017 11:07:14 »

Not all boilers have the ability to sense when all the trvs are shut which can lead to what is known as dry cycling where the boiler just keeeps heating water in its own loop usually around a bathroom radiator with no trv or a bypass loop. However, the room thermostat is rarely in a position to stop this happening.

My 35 year old system was installed with no TRV on the bathroom to prevent the pump trying to push water into a dead end, but auto bypass valves were introduced to prevent the need for this. Nowadays boilers like the one I'm getting have them integrated.

I currently have a boiler for space heating and a separate multipoint for hot water, so I'm replacing them with a combi so that I won't need to build an airing cupboard for a hot tank. With having a multipoint, I'm already used to waiting for the tap to run hot when I turn it on, but a lot of people who don't understand how combis work complain about it. In order to address this, the combi I'm having has been deliberately designed to 'dry cycle' so that the water jacket remains hot in order to reduce the time it takes for the tap to run hot when you turn it on.

With heating though, if it takes x watts to warm the house, dependent on the difference between the inside and outside temperatures at any given time, and the boiler power is y, then the duty cycle of the boiler stat will be x/y, and the frequency that it cycles at will be determined by the hysteresis on the stat. If you already have TRVs to set the room temperatures, then there isn't really anything to be gained by fitting a roomstat in between. For example, if a roomstat was operating at a duty cycle of 50%, then the duty cycle of the boiler stat (whilst the roomstat is on) would just rise to 2x/y in order to maintain the same mean power overall, and hence the same space temperature. The end result though would be that the air temperature in the room will cycle up and down by an amount equal to the hysteresis on the roomstat, whereas without it the temperature variation due to the boiler stat hysteresis tends to get smoothed out by the thermal inertia of the water and radiators.

22

Technology / Re: Why is a roomstat needed even if every radiation has a thermostatic valve (TRV)?

« on: 25/05/2017 22:17:50 »

The valve on the radiator can't know when the room has warmed up- because it's far away from most of the room, and very near the radiator.

So what's the point of it then?

It's cheap + easy.

Not really. Roomstats start at about £16, which is a lot less than 8 TRVs at £7, and a cheap roomstat will require the inconvenience of a wire to it unlike TRVs.

Attempting to control the whole house from a single thermostat which is isolated from all but one room when multiple rooms have radiators is crude and ineffective, but it prevailed in early central heating systems because it is cheap and simple. TRVs emerged as wealth increased because they are far superior, which begs the original question: why bugger up a good system with a roomstat?

23

Technology / Re: Why is a roomstat needed even if every radiation has a thermostatic valve (TRV)?

« on: 25/05/2017 13:27:25 »

The valve on the radiator can't know when the room has warmed up- because it's far away from most of the room, and very near the radiator.

The ratio of the temperature in the middle of the room to the temperature in the vicinity of the TRV is going to remain fairly constant as long as the room arrangement stays the same. TRVs are not calibrated in degrees, and are adjusted until the occupants feel comfortable anyway. Lastly, the TRV in the lounge knows the lounge temperature a lot better than a roomstat in the hall does.

The problem with a roomstat is not the location of the sensing, it's that it controls the whole system rather than independent control of each room.

Worcester Bosch give an extra 2 years guarantee if you fit their own roomstat rather than one from a third party, so I'm thinking that there's a reliability angle to all this that they're coy about discussing.

24

Technology / Re: Why is a roomstat needed even if every radiation has a thermostatic valve (TRV)?

« on: 24/05/2017 14:56:29 »

The plumber's happy to install it without a roomstat, it's me who doesn't want to get fined for a non-compliant system or give Worcester an excuse not to honour the guarantee. As I said to the plumber, I know I can stamp my foot and demand that I get my own way, I'm just trying to work out whether I'm missing the point somewhere. The problem is that the plumbers don't really seem to understand much beyond just repeating what they always do, parrot-fashion, so they just retreat into customer's-always-right mode and humour you as soon as you challenge what they say.

I've agreed that he will fit both a TRV and a roomstat in the hall, so I can set the temperature using either one or the other, and we'll see which way works best.

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Technology / Re: Why is a roomstat needed even if every radiation has a thermostatic valve (TRV)?

« on: 24/05/2017 12:36:21 »

I already have all the TRVs, so no expense there, I just don't want the roomstat because it will defeat the point of the TRVs. What I can't fathom is why I appear to be the only one asking questions like this, and why if I'm not the first one, nobody is giving me sensible answers. I asked Worcester Bosch technical dept., but they weren't interested, and told me to go and ask someone else.

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Technology / Why is a roomstat needed even if every radiation has a thermostatic valve (TRV)?

« on: 24/05/2017 11:34:32 »

I'm in the process of replacing my boiler, and I note that current building regulations require that a roomstat be fitted even on systems with a TRV on every radiator. WHY?, once you have TRVs throughout the house you have full and individual control over the heat in each room, and putting a roomstat in overall control of the whole house is defeating the point of having them.

For example, with a roomstat in the hallway as recommended, I might set the hall to a cool temperature to save heat whilst wanting a warmer temperature in the lounge. So when the heating comes on, the roomstat in the hall will be the first one to satisfy, because it's set to the coolest temperature, and then at that point the whole system will switch off before the living rooms ever get warm!! When I pointed this out to the plumber quoting me yesterday, he said "well you need to turn the roomstat up to maximum so that it won't cut out". When I pointed out it's a waste of heat turning the hall up higher than I want it just to stop the lounge going cold he said "well put the roomstat in the lounge then". So I then pointed out that the same problem exists wherever you site the roomstat because it's turning off the whole house when just one room is satisfied, and he didn't have an answer to that.

I had this same argument 35 years ago when the system was first put in, and at that time I was told that if I didn't fit a roomstat the pump would fail within a year. Well, there's no roomstat, and the pump has run just fine for 35 years.

It's barmy, it's like fitting a light switch in every room bar the hallway, and then using the consumer unit to turn the hall light on and off. Anyone with a little common sense can see that you wouldn't want the whole house plunged into darkness just in order to turn the hall light off, but they don't seem to apply the same logic to the heating.

27

Physiology & Medicine / Re: Should we take a small aspirin every day?

« on: 24/05/2017 10:58:57 »

Thus, antiplatelet therapy cannot be recommended for stroke prevention in AF patients

Your original statement i.e. "aspirin is no longer recommended for AF".... is only partly true --> aspirin is recommended in AF patients with NSTEMI or following angioplasty/stent-placement.

So is aspirin deemed better than warfarin (et al) for NSTEMI patients?

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Physiology & Medicine / Re: Should we take a small aspirin everyday?

« on: 28/04/2017 15:19:53 »

aspirin is no longer recommended for AF as the benefits are minimal, and the bleeding risk is just as high

This would only be true in AF patients at high risk of bleeding -
which is easily determined via the CHA2DS2-VASc score.

The current 2016 guidelines for the management of AF from the European Society of Cardiology state:

"The bleeding risk on aspirin is not different to the bleeding risk on VKA or NOAC therapy, while VKA and NOACs, but not aspirin, effectively prevent strokes in AF patients."

and:

The evidence supporting antiplatelet monotherapy for stroke prevention in AF is very limited. VKA therapy prevents stroke, systemic embolism, myocardial infarction, and vascular death better than single or dual antiplatelet therapy with aspirin and clopidogrel ............Antiplatelet therapy increases bleeding risk, especially dual antiplatelet therapy (2.0% vs. 1.3% with antiplatelet monotherapy; P , 0.001), with bleeding rates that are similar to those on OAC. Thus, antiplatelet therapy cannot be recommended for stroke prevention in AF patients.

The 2012 guidelines said much the same:

"The efficacy of stroke prevention with aspirin is weak, with a potential for harm, since the risk of major bleeding (and ICH) with aspirin is not significantly different to that of OAC, especially in the elderly."

The CHA2DS2-VASc score is for assessing the risk of additional ischaemic strokes due to the AF, the HASBLED score is for assessing the additional risk of haemorrhagic strokes due to anticoagulation. Comparison of the two tells you whether you're better off with or without anticoagulation.

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Physiology & Medicine / Re: Should we take a small aspirin everyday?

« on: 27/04/2017 17:48:44 »

However, some heart conditions can lead to excess formation of blood clots, which could pass to the brain and also cause a stroke or heart attack.

Which ones?

Atrial fibrillation

I wondered if evan_au meant AF, but aspirin is no longer recommended for AF as the benefits are minimal, and the bleeding risk is just as high as with Warfarin and other anticoagulants.

30

Physiology & Medicine / Re: What is the cause of gout, and how is gout treated and controlled?

« on: 22/04/2017 00:39:30 »

Does anyone know anything about a link between allopurinol and polyarteritis nodosa? I recall seeing something about 25 years ago, but I can't find anything much these days, so I wonder if it has been discounted.

31

Physiology & Medicine / Re: Should we take a small aspirin everyday?

« on: 16/04/2017 15:43:27 »

However, some heart conditions can lead to excess formation of blood clots, which could pass to the brain and also cause a stroke or heart attack.

Which ones?

32

Physiology & Medicine / Re: Why don't scars disappear as tissue is replaced over time?

« on: 07/04/2017 22:23:25 »

I have a 48 year old scar on my arm and a 53 year old one on my knee, they used to be very conspicuous, but you have to look quite hard to find them now.

33

Chemistry / Re: Why is cleaning fluid fluorescent?

« on: 11/03/2017 18:30:23 »

So does that work if the fluorescence is bright yellow rather than blue? This stuff looks like a workman's Hi Viz yellow jacket.
https://www.tesco.com/groceries/product/details/?id=253259214#r:sr:sr:38:1:1:52925779::c,search

34

Chemistry / Why is cleaning fluid fluorescent?

« on: 10/03/2017 13:23:56 »

I've just cracked open a new bottle of cleaning fluid (Tesco's equivalent of Flash) and it's fluorescent, startlingly so. So what's that about, is there any point, or is it just a gimmick?

35

Physics, Astronomy & Cosmology / Re: Does a microwave use the same amount of energy for all food?

« on: 07/03/2017 14:46:49 »

Looks like someone else didn't fully think through the ramifications of measuring power in a non-linear load too:
http://sciencebulletin.org/archives/10940.html

36

Physiology & Medicine / Re: How large is a food "portion"?

« on: 03/03/2017 13:31:52 »

Does anyone here actually eat five, or ten, portions of fruit each day?

Not fruit, but I average eight portions of fruit and veg a day.
(Edit: Just totted up, I've had just over 11 portions today.)

37

Physiology & Medicine / Re: How large is a "portion"

« on: 28/02/2017 11:07:05 »

Salt is another one that is specified as an absolute level rather than in proportion to calorie intake or body weight. I don't know whether that's correct, or just a simplification, but it makes the target more difficult to meet for those with a high calorie intake.

38

Physiology & Medicine / Re: Does the Brain Habituate to Antidepressants?

« on: 11/02/2017 14:14:10 »

"Antidepressant discontinuation syndrome" is a euphemism for drug withdrawal , which means adaptation has occurred.

Yes, I suppose when you put it in terms of withdrawal it's obvious, but I was thinking more in terms of the intended therapeutic effects.

39

Physiology & Medicine / Re: Is obesity a sin of gluttony or sloth?

« on: 11/02/2017 14:10:31 »

If I turn the heat up again, the cycle repeats until the heating is flat out and I still feel cold

One difference between individuals is due to levels of thyroid hormone, which impacts general metabolism

Curiously, the cycle works in reverse also: if I turn the heating down and put up with feeling cold for an hour or so, I start to feel a flush of warmth as my body warms up again. What I can't seem to achieve is a stable state that doesn't drift one way or the other.

As I have grown old (now 88) I find my weight 83Kg BMI 25 has changed little but I have lost muscle mass and made up for it in fat.

A year after I stopped training, my weight hadn't increased at all, but my rib cage had disappeared under a thick layer of fat. I was rather surprised that my doctor was puzzled by that.

This does not imply that their digestive system flushes out the food after 10-30 minutes! That certainly would limit the amount of calories that could be extracted*.

I understand that typical transit time for healthy individuals from eating to excretion of solids is 24 to 72 hours. So the person relieving themselves straight after a meal is getting rid of the residue from food they ate yesterday (or the day before).
This transit time is most obvious after a barium meal, due to its distinctive color and density.

Before I had surgery for a rectal tumour I had a barium meal, and it puzzled me at the time that I only had to wait an hour or so from drinking it to having the CT scan. I didn't have my bowel emptied with a laxative beforehand, and I wasn't passing barium drink immediately afterwards either.

The body does not extract more nutrients when someone is constipated.The main extraction of nutrients is from the stomach and then small intestine (80-90%). In the small intestine the semifluid material called chyme is constantly churned so that material against the gut wall is constantly changed to allow for absorption. The chyme then moves to the upper part of the large intestine where fermentation extracts some remaining starch and protein. Water extraction takes place progressively down the large intestine so that at the lower end firmer stools are formed, however, constipation is the extraction of too much water and means that fermentation is reduced and churning can't take place, so reduced extraction of remaining nutrients not more.
Unless someone is suffering from a disease which causes slow transit time, the times are as described by Evan above. An apparent slowing down is due to compaction of the stools and not an overall slowing down through the system.

This doesn't make sense to me, it's not the constipation causing extraction of more nutrients, if the speed of the whole bowel slows then the time the contents spend in the lower bowel will increase, and there is more time for water to be absorbed, making the stools firmer. If the transit speed slowed in the lower bowel but not the upper bowel the gut would inflate like a balloon.

40

Physiology & Medicine / Does the Brain Habituate to Antidepressants?

« on: 02/02/2017 16:11:04 »

I see people complain that they stop working after they've been on them for a while and think well, yes, why wouldn't they. The brain has evolved to habituate to its environment after all, why should antidepressants be any different to other things it habituates to?