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mixing valves

10 REPLIES 10
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Message 1 of 11
Elvis_DDA
1292 Views, 10 Replies

mixing valves

Is there any default family for a mixing valve? If not, when I draw my own, does the program recognise the mixed water temps and recalculate?
10 REPLIES 10
Message 2 of 11
Martin__Schmid
in reply to: Elvis_DDA

If not, when I draw my own, does the program recognise the mixed water temps and recalculate?
> No.

Interesting question though... what are you modeling and hoping to accomplish by such functionality?


Martin Schmid
Product Line Manager
Mechanical Detailing and Electrical Design
Architecture, Engineering, and Construction
Autodesk, Inc.

Message 3 of 11
jlwetzel
in reply to: Elvis_DDA

The most common i can think of is a thermostatic mixing valve for a shower. We've used tempered water in medical office projects as well.
Message 4 of 11
embolisim
in reply to: Elvis_DDA

We routinely use thermostatic mixing valves on the domestic hot water supply. If you store the water at a higher temp (say 85 deg C) your running costs are actually lower because you can get away with a smaller storage volume. We put the 85 (or 65, etc, it varies by application) in a pumped loop & mix it with cold close to the faucet (or group of faucets) to provide regulation temperature.
See if this makes sense:

Hot water temperature (loop) = Known
Hot water flow (loop) = calculated based number & demand of tempering stations on the system.

Cold water temperature = Known
Cold water flow = calculated
===========================
Tempered water temperature = Known (per local building regulations)
Tempered water flow (demand) = Known (fixture damand)


So I know what the demand conditions are for temp and flow.
I know the supply conditions for temp only.

I wish to calculate the supply flows needed to achieve the demand conditions.

Currently the engineer does this by hand.

Are you sure this cant be done already, using parameters whith formulas? I have in mind to try, but I need to get a lot better at families first.
Message 5 of 11
Elvis_DDA
in reply to: Elvis_DDA

Thanks, that makes a lot more sense. Will keep it in mind when I come to do it. For the moment I've drawn a family with connectors, but they currently have no parameters set up.
Message 6 of 11
embolisim
in reply to: Elvis_DDA

Cool. Please post back if you get it working.
I have some Jgrumat mixing valve families. The 3400.956 & 3400.256
We are not supposed to share them, but if you are going to develop it then give it back I will.
Message 7 of 11
jade.l
in reply to: Elvis_DDA

I felt it hard to have this calculation function on through settings in family editor.

It would be a formula like this, if I understand the case correctly,
C(cold water)*m(cold water)*(T2-T1)= C(hot water)*m(hot water)*(T3-T2)

C is the specific heat for water, m is the mass of the water, T3 is the original hot water temperature, T2 is the temperature after mixing, T1 is the original cold water temperature.

What you want is the m(cold water). However, the m(hot water) is a case-by-case parameter which you can't know until in a project enviroment, thus you can't get the m(cold water) by defining formula in the family editor.

My guess, by shared parameter will be help, but some complex....

embolism, can Jgrumat mixing valve families calcutate the cold water flow? Thanks!


jade.l

Message 8 of 11
embolisim
in reply to: Elvis_DDA

The ones we have one of our grads made. They dont calculate anything at present (but they look very pretty) I'm hoping to add this at some stage, but its on a very long development list & far from the top.
Message 9 of 11
Elvis_DDA
in reply to: Elvis_DDA

same here, loooooong list. always seems to get longer than shorter.
Message 10 of 11
Martin__Schmid
in reply to: Elvis_DDA

To restate the 'knowns' and 'unknowns' to establish a formula, we have:
Knowns:
• HWT (i.e., 85deg)
• CWT (i.e., 15deg)
• TWT (i.e., 60deg)
• TWF (i.e. 100l/s)

Unknowns
• HWF
• CWF

Thus we have two unknowns, and we need two formulae to determine the values:
• HWF+CWF=TWF
• HWT*HWF+CWT*CWF=TWT*TWF

To solve for the flows, you can rewrite the formulae:
• HWF=(TWT*TWF - CWT*TWF) / (HWT-CWT)
• CWF=TWF-HWF

Plugging in for this example
• HWF = 64.3l/s
• CWF=35.7l/s

If we imagine a mixing valve to represent the mixing process, with ports named 'HW in', 'CW in', and ‘TW out', and you have assigned Systems to your supply piping (HW in and CW in), Revit knows the HWT and CWT because these are properties of their respective systems.

Revit also 'knows' TWF because it computes from the connectors at the 'points of utilization', and knows the TWT because you'd also create this system, and assign the temperature. We need to find ways to access the ‘known’ information, run the computation, then assign the values to the mixing valve’s connectors.

The problem is that there is no 'built-in' way to get the Systems' temperatures via parameters on the connectors of the valve. You could add your own params to the valve, and manually populate the values. You could use the API to extract the values and assign them to the params. Or, if you're using the API anyway, you could compute the values for the flows and assign to the connectors, and not necessarily use a param as a storage mechanism for the temperatures.

HTH,
Martin Schmid, PE


Martin Schmid
Product Line Manager
Mechanical Detailing and Electrical Design
Architecture, Engineering, and Construction
Autodesk, Inc.

Message 11 of 11
embolisim
in reply to: Elvis_DDA

Thanks Martin, thats very helpful.
I'm going to have to try it out now.

I think manually entering the temperature is ok as its something that is pretty consistent across the projects we do.

It also follows that I can schedule the values for the engineer to check.

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