Volume of Expansion for Hot Water

You need the steam table logs isp.

http://www.simetric.co.uk/si_water.htm

http://www.simetric.co.uk/si_water.htm

Hi! Thanks for the links

Since you know the volume of water and the operating temperature you could work out a volume of expansion required to allow for expansion from, say, room temperature to operating temp. Your expansion tank/volume would then be able to cope with a from-cold start up without loss. If using an accumulator of course you would needs to size it in regard to the pressure difference the system was capable of sustaining. I can't think of another temperature range you might want to do it for but it would be best to allow for a situation where a fault meant higher than operating temperature and you'll of course still need a means of dealing with over-pressure.

Are steam tables that necessary for this temp range?.

(Wrenched)

Hi! thanks for the input. one of my engineer have sized-up the expansion tank which i feel that it is over the capacity. the hotwater from the hw boiler (70deg C) will be use through heat exchanger by heating the water also for fan coil units of HVAC system. both sides will be close loop system.

Now, Since it is close loop system on the boiler side, you need the expansion tank for water expansion, and it can be use also for air removal on the system IF the expansion tank is elevated (above boiler level). however, the expansion tank elevation is the same on the boiler unit elevation. As suggested by myself, the system flow or on top of the boiler shall have a air vent valve for immediate air removal during start-up, and couple of air vent valve also on the piping system on the higher level.

Since it is close loop system, in your opinion is it recommended that there will be a check valve between the connection of piping of expansion tank and the boiler? if so, where is the location of make-up water feed line?

Jojie_oak@yahoo.com

Hey, I'd better start off by saying I've never 'designed' anything more than my home central heating system so I could be totally off track.

You must have in mind an operating pressure range and, as mentioned, an operating temperature range in mind. From the temperature range you can work out the thermal expansion of the water. I think I'd neglect the expansion of the pipework and regard it as 'safety factor'. From the temperature range you can apply P*V/T and get an estimate of the change in volume due to temperature, or the steam tables for better accuracy. Now knowing the change in volume due to these factors, you can find the volume that will keep your pressure within operating range. I 'd allow something significant for a safety factor though, and not close the system until tests had shown that it was about right! I'd be inclined to position my safety valve in the high pressure zone just after the boiler and run it safely away to a drain or somewhere that hot water won't hurt anyone. Releasing over-pressure as steam is more dangerous isnt it?

What pressure is your water supply and what pressure do you expect the system to run at?? I guess it would be conventional to have the make-up feed at the point of lowest pressure? e.g. the pump inlet? I'm not quite sure why you need the system to operate closed. i.e. without a 'header' tank which is open to atmosphere? Perhaps because you can't site a header tank anywhere high enough?

Hope someone with real experience comes along soon.....

I don't know if this is to the point or not, but that never stopped me before.

We typically allow for 1/8" per foot expansion for every horizontal change of direction with Hot water, specific hanger and support spec to counter sagging when installing inspecting and testing HUPW systems piped in PVDF , PVC, or polypropylene.

I am having trouble pin-pointing your exact concern.

The volume of water isnt' going to change beacause you heat it. If you heat a gallon of water you still have 3.7854118 L of water.

The pressure will increase, thank you Mr. Boyle, but you don't get more of the wet stuff.

Now your material that you are transporting/piping or holding the water in. That, like the water will probably expand. Depends on the material. And all material have their own expansion factors and are dependent on temp and pressure.

CR3

So you opine that the coeff. of themal expansion of water is zero, nothing, nil? I have it as about 4 times that of copper, so if you are using copper, or worse steel pipework you need to design in something to accomodate it.

As I re-read I see my confusion.

No I am not arguing that heated h20 does not expand. I have boiled water, though not recently. (she IS so good to me)

The point I was making was that there is not going to be more water. It will occcupy more space or incraese pressure, but it will not self replicate. A point I did not need to make and therefore apologize for making, having re-read initial question and subsequent additions.

so please read, my friend Wrenched I am sure you will appreciate this. Hot water expands. In a closed, filled system the material containing the water will expand too. The pressure will increase if the H20 expands more than the piping. (we all know this).

You know what....never mind for now. I need my coffee. I cant believe someone asked me if I believed that water didn't expand when heated. Geez. Is it Monday again?

cr3

It seems to be mostly me making tea/coffee round here. Actually it's mostly me drinking it too! I've never checked on the expansion when making it. I'm prompted to ask myself, although I was probably told (darn long time ago) what the definition of a litre is, or was (it hasn't changed has it??).

Although the questioner appears to be thinking of keeping the system open during warm up (I'd say unusual), in which case there's no need to make provision for it.

C_Rummel3: If it were true that metal expanded but water didn't, an engine wouldn't have an expansion tank. I think rather the water level in the radiator would fall as it warmed up?

CR3,

I do understand the piping expansion base on temperature & pressure concern. we always take this factor during piping installation with API 5L & 312 Piping materials.

On the HW system at contineous flow with return system to maintain the temperature on the piping, this is normally used in Hotels and hospitals, expansion tank is always there.

See the link mentioned from our member/guest comments on this forum. that link is a standard table and ready referrence.

jojie_oak