PDA

View Full Version : OT Hot water systems



SDL
04-16-2009, 08:07 AM
Questions

In the USA in comercial situations like hospitals is the hot water for sinks etc stored in a heated tank or because of the length of the runs is it circulated through a ring with draw offs?

Do they ever add extra chlorination / disenfection chemicals?

I ask as we supply some Filter housing made of 316L stainless steel and we have seen crevice corosion which you dont normally get on potable water only on things like fish farms with sea water or spa pools etc.

Steve Larner

Puzzled in the UK

Evan
04-16-2009, 08:47 AM
I would expect that in a modern hospital the water would be heated at point of use with a demand heater. Chloride induced corrosion could just be from a domestic water supply with high chlorine levels. I know from my experience that some city water supplies smell like a public swimming pool the chlorine is so strong.

JCHannum
04-16-2009, 09:00 AM
I am not familiar with hospital systems, but a circulation loop could be a possibility. It is also possible that the water, especially if used for sanitation of equipment and facilities has chlorine added and is at a much higher temperature than would be used for normal household uses such as bathing and personal use. Both of these would contribute to the corrosion you are seeing.

Separate systems for sanitation purposes are not uncommon in the food industry, and could also be used in hospitals and such.

wierdscience
04-16-2009, 09:01 AM
Point of use in patients rooms,boiler or loop heat exchanger for facility wide systems.

At least that is what I have seen in newer hospitals.Older ones will be boiler feed or heat exchanger based only.

Electrolisis could be a factor,although chlorine and flouride are present in most municipal water supplies.

It's also possible for chlorine and flouride to build up in remote areas of a complex piping system or buildings with multiple floors.

Di-electric unions(threaded) or gaskets(in case of a flanged connection) are usually used to eliminate electrolisis action.

oldtiffie
04-16-2009, 09:03 AM
In the hospitals in which I had to look after the maintenance in, the hot-water had to be at least 70 degrees C (~158 deg F) at the outlets in patient and surgical areas as well as in hand-basins and showers to kill "Legionnaire's Disease" "bugs". The hot water was heated in central boilers and recirculated around a "live" ring-main so that hot water was on instant supply/demand with no "cold spots" or delays. It may have been "tempered" (cooled) at the outlets. Our outlets were serviced at least at 6-monthly intervals.

Same applied to our accommodation blocks etc. (Military).

All our cooling towers (lots) were dosed and serviced very regularly as well.

So far as I can recall, our chlorinated and flouridated domestic water supply had no additional "dosing".

All was as required by Australian Standards.

I would guess that is pretty well standard else-where.

Circlip
04-16-2009, 09:16 AM
One of the reasons we don't use Stainless for toy engine/loco boilers on OUR side of the pond Steve.

Regards Ian.

Andrew_D
04-16-2009, 09:57 AM
I have also seen hot-water loops used in small apartment buildings. If you think about it, it makes sense:

Small Apartment Building, 4 suites per floor, 3 floors. If the guy on the top floor opens the hot tap and has to wait 5 minutes for the hot water to get up there, he's pouring a lot of money down the drain. Now if everybody does this 4-10 times per day, you're going to recoup the cost of a re-circulating pump, pipe and insulation pretty quick depending on what your water cost is.

A small re-circulating pump is used to keep the hot water moving through out the whole building. The hot water line should be insulated as well. Just remember that you need a way to keep the re-circ pump from pushing the hot water back into the cold lines. Typically a check valve is installed where the hot water from the HWT/Boiler/??? enters the loop.

Andrew

hardtail
04-16-2009, 10:53 AM
I think WS has nailed it..........

The point of demand systems (ind/com/res)have just started to make their way over here in the last decade not like the widespread use in Europe, I would say most would be supplied from live circulating loop/tanks but there maybe special requirements where they boost temps, I doubt they are adding extra chlorine, they have germs in hospitals now that have mutated and can party on it..........

Evan
04-16-2009, 12:19 PM
Point of demand heaters for uses such as hand washing have been around here for decades for institutional use. They usually have a small storage tank of a couple or so gallons and fit under the sink. By using a small tank the electrical load is considerably reduced compared to a true demand only heater.

SDL
04-16-2009, 03:38 PM
One of the reasons we don't use Stainless for toy engine/loco boilers on OUR side of the pond Steve.

Regards Ian.

True but the main concern there is chloride stress corrosion cracking (CSCC) This is crevice corosion which is rare on potable water.

Steve Larner

SDL
04-16-2009, 03:40 PM
In the hospitals in which I had to look after the maintenance in, the hot-water had to be at least 70 degrees C (~158 deg F) at the outlets in patient and surgical areas as well as in hand-basins and showers to kill "Legionnaire's Disease" "bugs". The hot water was heated in central boilers and recirculated around a "live" ring-main so that hot water was on instant supply/demand with no "cold spots" or delays. It may have been "tempered" (cooled) at the outlets. Our outlets were serviced at least at 6-monthly intervals.

Same applied to our accommodation blocks etc. (Military).

All our cooling towers (lots) were dosed and serviced very regularly as well.

So far as I can recall, our chlorinated and flouridated domestic water supply had no additional "dosing".

All was as required by Australian Standards.

I would guess that is pretty well standard else-where.

Thats how I imagined it but some of the experts at work think it will be like a house with no idea of the amount of water to run out the pipe first thing in the morning.

Steve Larner

SDL
04-16-2009, 03:42 PM
I am not familiar with hospital systems, but a circulation loop could be a possibility. It is also possible that the water, especially if used for sanitation of equipment and facilities has chlorine added and is at a much higher temperature than would be used for normal household uses such as bathing and personal use. Both of these would contribute to the corrosion you are seeing.

Separate systems for sanitation purposes are not uncommon in the food industry, and could also be used in hospitals and such.

Is it typical to add more chlorine at some plants where the water comes in, we have assumed that the chlorine would be at typical mains level?

Steve Larner

SDL
04-16-2009, 03:47 PM
Point of use in patients rooms,boiler or loop heat exchanger for facility wide systems.

At least that is what I have seen in newer hospitals.Older ones will be boiler feed or heat exchanger based only.

Electrolisis could be a factor,although chlorine and flouride are present in most municipal water supplies.

It's also possible for chlorine and flouride to build up in remote areas of a complex piping system or buildings with multiple floors.

Di-electric unions(threaded) or gaskets(in case of a flanged connection) are usually used to eliminate electrolisis action.

Hadnt thought about the Fluoride but that would add to the risk of crevice corrosion, any idea of temperature of circulating systems. is it over 70 (158f) because of legionnaires.

Steve Larner

SDL
04-16-2009, 03:49 PM
Thanks for all the ideas guys, confirms my line of thinking and will argue the case with more conviction,

Steve Larner

JCHannum
04-16-2009, 08:05 PM
Is it typical to add more chlorine at some plants where the water comes in, we have assumed that the chlorine would be at typical mains level?

Steve Larner

It is not unusual to increase the chlorine level in water for sanitation purposes. At the canneries where I worked, it was standard procedure to use one level of chlorination when processing, washing fresh fruit, etc. and to jack the level up for cleanup purposes. It did play billy hell with the piping systems and heating equipment. We usually used shell & tube heat exchangers to heat the water and life was short.

wierdscience
04-16-2009, 08:21 PM
Hadnt thought about the Fluoride but that would add to the risk of crevice corrosion, any idea of temperature of circulating systems. is it over 70 (158f) because of legionnaires.

Steve Larner

It depends,some states require mixing valves so the temps never exceed a set level(anti-scalding fixture).Never seen any data on water temps for hospitals,but commercial strutures IIRC run 140f max.

What about water softners?Those are common in many locales here at the building level as is the use of Bromides and Ferritic sulpher in water treatment at the municipal level.

JCHannum
04-16-2009, 08:26 PM
The anti-scalding and 140*F systems are for personell washing. It is possible a separate system is used for housekeeping ansanitation that operates at a higher temperature.

Secondary water treatment systems, softeners, RO & DI systems can add another source of problems.