I was browsing through some old posts (there are so many here; how do you choose what to read?) and I read about hot water circulating pumps that are supposed to get hot water to the taps quicker.
This sounds very good. In our house the HW goes from the cylinder to the bathroom, then drops into the kitchen, where it goes into the concrete floor and over to the sink. None of it was lagged. I have tried to lag various parts when I have had different floorboards up but obviously the run under the kitchen floor is inaccessible. It takes ages to get hot water to the kitchen sink. One of these pumps might be a good idea.
However, I am unsure how they work. Do you need to run a return pipe? Do they constantly circulate hot water around the house? If so that would be very impractical because surely you would need to plumb the hot water in a ring main, rather than the traditional radial style and have a return pipe? Also wouldn't this be uneconomical because you would constantly be losing heat through the pipe work rather than keeping it in a well insulated cylinder?
Or is it that the pump only comes on when a tap is open and just increases the flow so that the hot water gets there quicker, like a power shower?
Is there a special pump for this purpose and what are they called?
Yes, typically smaller than the main feed pipe so you could run it in
8mm or 10mm copper or 10mm plastic.
Well, that's what you have to do if you want such a system. It's more commonly used in larger, commercial or industrial premises.
Yup, but then you don't throw away heat and water running off warm water to get it hot.
No it runs constantly (preferably on a timer so at times of low demand you can still get got water (if it's available) but you have to run off the cold.
Usually bronze pumps (though plastics and stainless steel might be used)
You'd lose even more heat circulating constantly-hot water through uninsulated pipes in screed. Since you'd have to run new pipework for the return ayway, I'd suggest scrapping the existing pipe and installing a new, more direct run of well insulated pipework. You could use plastic for easy installation.
yes, usually; often timer controlled, PIR controlled, flow-switch, etc..
Usually a 15mm return from close to each fitting that you want to get HWS from quickly. These connect to the 15mm return. The flow rates are matched to the pipe heat losses and are usually tiny, so you should have low-flow DRVs/needle valve on the returns. Ball/gate valves are carp for this; they only regulate on the last fraction of the opening. Shut the valve and the carefully adjusted setting is lost. DRV are locked at the setting and can be closed and reopened only to the set opening.
For your installation, yes. For properly installed and insulated systems, no; small heat losses. Also much used commercially to ensure the water is never tepid and not a legionella friendly environment. HSE requires 50 degC within 60 seconds from all hot taps. Domestic users remain at liberty to host legionnaires' disease in their water systems. And they often do. Ignorance is bliss.
Could be, flow switch. But you really need the pump running before you operate the tap, the flow rate should be slow. You could open & close tap and then wait, but it's only saving you wasting water.
Must have a bronze impeller. Conventional CH pumps are often fitted and much replaced, the impellers rust very quickly. Grundfos do a domestic one, can't recall the name.
I would be fascinated to see evidence that Legionnaires is a problem in domestic systems. I am aware of only one case where someone has contracted it from a domestic system; this was the first use of a summer cabin in the USA, and the victim was already feeling ill before they used the shower with water that had sat for months.
On the other hand - scalding is a major problem. There are many examples under "scalded bath" on google; I can't say how many, as some hits are for chicken processing and the like.
On Sun, 03 Feb 2008 16:48:44 +0000 someone who may be Andy Champ wrote this:-
So would I.
Having spent many years looking after hot water systems in buildings I am not ignorant on the subject. I am not particularly worried about it either. There are other dangers in a house which are more important to pay close attention to.
Can you suggest any reason why domestic systems wouldn't grow legionella, given favourable conditions?
It's not a criminal offence to infect someone by means of an offrnsive domestic water system, so the HSE would drop all interest when the source had been identified. It's hard work to get them to shift their pin-striped, civil service backsides when there is a criminal offence involved. Unless there's a fatality they're not interested.
Eatherton. I posted that on here some months ago.
They are two entirely different problems with different solutions. The only connection is if you try to fit a central blending TMV and try to distribute at
I don't think anyone's suggesting domestic systems don't grow legionella. I suspect people with legionella in their domestic systems have built up immunity to it. Legionella occurs naturally in rain, and we've probably been immune to it for thousands of years. It only started becoming a problem in the last few decades when people starting trying to create biologically clean water systems, and hence lost their natural immunity to legionella. Then when exposed to another water system which isn't biologically clean (typically in a public building), they are vulnerable to the bacteria.
"However, this disease usually occurs as a single, isolated case not associated with any recognized outbreak."
I'd think that there were few aerosols of contaminated water around in the past few thousand years. Not many humidifiers, cooling towers, showers, hot tubs, etc., etc..
If you inhale a heavily infected aerosol, you'll probably get infected. If you're ill or elderly, you'll probably die.
'Not assocaited with any recognized outbreaks' probably means they test the commercial systems the victim has been in contact with. No match. no case, end of effort.
I suspect people with legionella in their domestic
Interesting theory. This bloke wants to install a centralized TMV; he thinks it's a good idea.
On Sun, 3 Feb 2008 09:06:12 -0800 (PST) someone who may be Onetap wrote this:-
I suspect that it does happen occasionally in domestic settings. However, does not offer any evidence that it happens.
Due to its far greater volume a calorifier provides for many more of the little nasties to rapidly multiply compared to a domestic hot water cylinder.
Circulation systems can be particularly prone to rapid multiplication if not operated properly.
There are rather less aerosols in a domestic setting.
However, in these days of saving fuel a domestic system may have its temperature turned down too low by a householder who doesn't understand the issues.
On Sun, 3 Feb 2008 10:57:01 -0800 (PST) someone who may be Onetap wrote this:-
There is nothing theoretical about the little nasties being in the rain.
As for natural immunity, I suspect there is something in that as we have immunity to all sorts of little nasties. However, immunity is not 100% and neither is it a binary condition. People's immunity levels are lowered by various things and when immunity levels are lowered an infection is more likely.
None at all. Nor any reason why I shouldn't get Weil's disease every time I go sailing (dinghy, on a gravel pit). Nor any reason why I shouldn't get E.Coli poisoning from getting a faceful of water that the ducks have been s***ming in.
But it's not enough of a risk for me to care about.
Andy
(though if I should get flu bad enough for the doctor to be needed, Weil's would get a mention...)
Calorifiers (storage) are big hot water cylinders. The commercial ones now have drains at the lowest points, access flanges for cleaning, domed bases where limescale cannot accumulate, BMS monitoring and, usually, pasteurisation pumps to get all the stored water above 60 degC at regular intervals overnight.
Domestic cylinders can suffer stratification, an accumulation of limescale and nutrient material in their bases and water stratification, allowing legionella to colonize their lowest and coolest corners. Unlike their big brothers they have none of the safety features mentioned above and are generally never cleaned out.
Which > None at all. =A0Nor any reason why I shouldn't get Weil's disease every
It's a free country, you do that if you like. You think it's not a big risk, but do you have the experience to form a realistic assessment of the risk?
ISTR that when this first hit the NHS, in about 1985, they started removing DHWS heating pipe loops in bathrooms, installing point-of-use TMVs and auto-draining shower hoses. At that time there was a document circulated that mentioned tests involving laboratory animals and an aerosol.
The infection and fatality rate was 100%. I can't recall what the document was, it was 20+ years ago. I remember the 100% figure because it scared the crap out of me. I think the risk may be bigger than you think.
On the Continent domed bottoms are common wit a pipe at the bottom to prevent buiold ups as there is always a flow through. I only know Gledhill, who make a domed bottom cylidner, a twin cylidner version. They also use it for a thermal stores and use the DHW pump as a shunt pump to evenly heat the store. This is where thermal store/heat banks score well. The DHW is heated over 60C and blended down.
yep.
All cylinders should be domed bottomed with the cold feed at the bottom to give full flow through the cylinder. Flat bottomed have a dead zone of stagnant water.
On 4 Feb, 23:14, "Doctor Drivel" wrote: =A0This is where thermal store/heat banks score well. =A0The DHW is
They heat it to 80 degC then blend it down with a TMV. At that temperature, all the dissolved limescale drops out of solution and clogs up the heat exchanger coil. They are commonly known as sludge buckets, for good reason.
Ok, here's one, a Dutch survey; I haven't read it all, no time, too late.
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the summary; "We demonstrated in our study that LD in Dutch travelers might have its origin at home. Traveling may be a risk factor for exposure to Legionella spp. in the patient's own residence by causing standing water to become stagnant during warm seasons, provided that legionellae were already present in the water system."
Stagnant water during warm weather. That's similar to what happened to Mark Eatherton.
Another Italian survey, 13 pages;
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top of P6; "Legionellae concentrations of 3-7,000 CFU/L could be sufficient to produce one case per year in a susceptible population (43), and these contamination levels correspond to those found in our study at the domestic level. In a recent epidemiologic survey on seropositivity in residents of homes with and without Legionella in the water systems, the prevalence of antiLegionella antibodies was twice as high in persons in homes with legionellae as in those persons whose homes did not have legionellae (44). The antibodies were most likely the result of asymptomatic infections caused by exposure in their home water supply, as no cases of pneumonia in the exposed population were reported. Most cases of sporadic legionellosis are not reported to health authorities in Italy as well as in other countries, and finding an association with a specific source of infection such as domestic contamination is rare (45)."
No-one's much interested in surveying houses because house holders have no legal duty of care to themselves or their families.
Which supports the Andrew Gabriel legionella anti-bodies theory; the git. If you're elderly or ill, you'll quite likely die before any anti- bosies show up. Some domestic systems are mind-bogglingly minging.
An American one;
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of Page 1109; "Our findings on a limited number (five) of single-family houses suggest that Legionella may occur infrequently in the plumbing fixtures of these buildings. We speculate that this infrequent occurrence may be related to the type of hot-water tank that is present. Houses in which legionellae were not detected utilized modern hot-water tanks. In these tanks, the heat is applied at the bottom of tanks, thereby maintaining temperatures which kill the bacteria accumulating there. In contrast, the legionellae were present in the water and sediment at the bottom of an older domestic tank which had a sideburner to heat the water. The temperature at the bottom of this tank was within the range for the growth of L. pneumophila. Interestingly, this home was the only one in which L. pneumophila was recovered from a plumbing fixture. The sampling of hot-water tanks in additional homes is needed to test this hypothesis."
On Mon, 4 Feb 2008 14:26:48 -0800 (PST) someone who may be Onetap wrote this:-
Both.
However, the presence of the little nasties is of no concern. What is of concern is the rapid multiplication of the little nasties to a dangerous concentration.
At the risk of being seen to be too blunt, panic is not a good reaction. People have certainly been killed by the little nasties. However, people are killed by many other things, including stairs. All these risks should be managed properly, going overboard on one of the risks simply means attention is taken from the other things.
There are several different Legionella, so it depends which ones are present in a particular source of water as to whether there is any risk of either of the two main Legionella related diseases, Pontiac Fever and Legionnaires' Disease.
According to WHO figures, only about 20% of cases in Europe are travel related. Quite a high proportion are hospital related, probably because the main personal risk factors are also likely to put people in hospital. There, aspiration (inhaling water in the mouth) is considered as much of a problem as inhalation of aerosols, particularly among patients with breathing difficulties.
They attribute the apparent emergence of the diseases in the past few decades to improved detection of a disease that tends to have non-specific symptoms. The distribution of the bacteria is similar around the world and there must be plenty of poorly maintained air conditioning plants in tropical and sub-topical third world cities, but the cases are generally reported in places with good healthcare.
The WHO is confident that it is a problem in all water systems and that some cases can be attributed to domestic water systems - the main risks being aerosols generated by showers and toilet flushing. However, as complex water systems with areas that can hold stagnant water are at higher risk of developing hazardous levels of bacteria, domestic systems are at a lower risk than most commercial systems.
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