Thermostatic mixing valve with dynamic temperature setting based on flow rate?

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Jeff Phillips

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Upper Peninsula, Michigan
Is it possible to rig up the plumbing with a thermostatatic valve in such a manner that it only attempts to mix in hot water to bring the water temperature up to the desired minimum when the flow rate is over a certain threshold? Or better yet, have the temperature set point of the thermostatic mixing valve somehow dynamically change based on the current flow rate at any given moment?

For example. Lets say I have an apartment building in which tenants pay their own electric and have 112.5 amp tankless electric water heaters in each apartment. But, on the most extreme cold days of winter, the incomming water temperature may be too freezing cold for them to keep up depending on the current flow rate gpm demand at any given moment. If its unable to provide adequate hot water, then I would like to have some sort of thermostatic valve mix in some hot water from the common area laundry room gas water heater which is on the landlord utility bill.

But heres where its tricky to me. If i were to plan on it needing sufficient flow rate to support one shower plus one sink faucet on simultaneously for each apartment's tankless heater, then I know there are going to be days in the winter when the incomming water temperature is too cold and the tankless electric unit wont be able to rise the water temperature enough. But.. when the current flow rate being demanded is lower--then the tankless heater would be capable of rising its temperature more so. When that low gpm flow rate is happening then its acceptable for the incomming water to be colder.

So i want to know if there is a way to rig up a thermostatic mixing valve to mix in more hot water from the laundry room water heater to rise the cold water temperature up to at least the minimum temperature necessary for the electric tankless heater to then heat it the rest of the way up by having all of its heating elements on its different breakers all on and actively heating the water.

I do not want to mix hot water in from the laundry room heater to raise the incomming water temperature supplied to the tankless unit based on a calculated assumption that we want to provide adequate hot water for a shower and sink faucet to both be in use together, during times in which the shower isnt even on and only the sink faucet is in use requiring a much lower overall flow rate. When the flow rate is very low, i want to keep the incomming water cold and let the electric tankless heater kick on all of its heating elements to the max to heat it entirely on its own. I do not want to have a thermostatic valve mixing in hot water from another source to bring it up to the minimum input temperature necessary to support anticipated potential gpm flow rate demands that are higher than the actual present flow rate, because that would cause the tankless heater to see the water coming into it is already lukewarm and if the current flow rate gpm demand is low enough then it would only kick on one or two of its heating elements instead of all three. How i want it to work instead is only when all three heating elements already kicked on, then if that still isnt enough, then use a thermostatic mixing valve rigged up to steal a little hot water from the laundry room (gas bill) so as to ensure that as much as possible we use the electric utility bill more and minimize natural gas consumption. So i dont ever want the hydrostatic mixing valve to mix hot water in from the laundry room while the tankless heater then only uses some of its heating elements as that would be a financial loss to us since we are only responsible for the gas bill, not the electric bill.

Is there a way of plumbing in thermostatic mixing valves to only attempt to mix in hot water to raise to a minimum specified temperature ONLY when the flow rate exceeds a certain threshold?

Is there any thermostatic mixing valves that can have multiple set points depending on current flow rate?

That is to say if its currently 5 gallons per minute, make it mix more hot water in to bring the minimum temperature up to a higher number of degrees than if its say 3 gallons per minute, and to not let it mix any hot water in at all if its under 1 gallon per minute... Or something similar.



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Peace valley missouri
You can have the complicated programming it will take for your heaters. Flow meters at each w heater with wiring going back to a processor. Mixing valve with temp sensors and flow meter for gas w heater. A company that does energy management or industrial controls for programming and all the hardware. Thats if the cold water supply to each heater is separate from the rest of the cold water lines.
Hey, wait a minute.

This is awkward, but...

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