In hot water...

Help Support and Requests
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Ran into a new problem last night.

The instant hot water heater powering our Autovap decided it had better things to do with its time and electrickery than help me recover solvent

Current diagnosis is that the flow sensor doesn’t like hot water!

I believe we’ve got a replacement sensor coming, but I suspect that is just going to kick the can two weeks down the road rather than solve the problem.

We’re looking for one rated for the temp now.

Question: why has nobody else raised their hand on this one? Why have the last 1/2 dozen similar installations (smaller, for hydrocarbon recovery) run for months without issue? Is it just Hubbel that got it wrong?

I suspect the smaller units don’t have actuall flow sensors, and use temp as their control point.

Wondering if anyone had any insight before I teach this heater how things are supposed to work, using non-oem parts…

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Got some pics of the setup?

Depending on control scheme could certainly have stuck in heating position and gone over the temp the flow sensor was rated for.

Most electric water heaters don’t even bother with a flow switch or sensor because they’re always being fed with pressure from a well or city water and not using a water heater in a closed loop setup. The ones that do (like in hot tubs for example) do tend to use flow switches since those heater elements really don’t like to be run dry.

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Replaced it with the bigger one we needed to have installed in the first place.

Might have access to the old one, or it might have wanderd off. Definitely overheated the flow sensor. I’m guessing the smaller ones I’ve interacted with have been sans sensor.

If the lower wattage unit is still in site I’ll try and document the issue.

My understanding is that this was the water heater the OEM spec’ed to go with the FFE.

So I expect others may run into overheated flow sensors too…

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If its any consolation the heater I’m building for my soon-to-arrive FFE is going to be fitted with a flowmeter that can handle 250*F. Going to use an alarm relay that takes a 4-20 mA input to enable the SSR that powers the heating elements

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You got a part number on that flow meter??

that would help console me :slight_smile:

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Obviously what you want will depend on what size pipe and whether you’re going to be using threaded, flange or other connections, but here’s a good starting point for you if 1" NPT will work for your scale:

https://koboldusa.com/products/flow/variable-area-flowmeter-and-switches/smn-flow-switch-liquids

Here’s all their flow measurement offerings:

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Here are some photos of the items in question, Sir @greenbuggy, in repayment for your very helpful answer!

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To clarify, @cyclopath, the smaller TX model Hubbell on-demand water heater’s inlet flow sensor (3/8" male NPT, I think, shrinking the inlet diameter down from 3/4" sharkbite fittings and copper pipes) states a rating of only 158°F, which does not pair well with TruSteel’s AutoVap operating temperature of 190°F… and that’s the one that died after perhaps 1.5 weeks of continuous use (when evaporating and when draining or stopping evaporating in the AutoVap).

To further obfuscate the issue a bit, the rating on the newer HX model Hubbell’s inlet flow sensor (full 1" compression fittings from 1" sharkbite and pipes) is stated at 85°C… which is 185°F… which means the smaller sensor’s label might just have a typo, swapping the 8 and 5.

We are running the heated water with a Taco 1/8HP continuous duty floor-heating pump on over 100 feet of 1" pipe and insulated heater hose. On the restricted TX, the flow was about 2.5 GPM, and on the HX, the flow is about 8.5 GPM.

Previous on-demand water heaters we used for large BHO system boilers only needed set around 90 to 110°F to get the resin concentrating job done. They were “Eco” brand or models, I think. We ran them on a much shorter loop, using a fast-flowing plastic hydroponics pump.

My solution, for now, is setting the water heater to 185°F… so the outflow hovers around 192°F, and the inflow returns at 172°F (vacuum evaporating) and 182°F (no vacuum or evaporating), max.

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Our apologies for this problem. I’m hoping by the lack of further response that the unit is working with no issues now. Hope you like your evaporator!

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Thank you.
We do.

I’m willing to agree that an on demand water heater shouldn’t do a lot of heating with 185f input.

I’m not certain that a flow sensor that fails at that temp qualifies as a feature.

We are working off label here, and we either need to address the deficiencies or find the right tool.

At this point the can has made it two weeks down the road…

We upgraded the heater because we upgraded from an AV15 to an AV25 mid flight. I don’t consider it a solved problem, but given I’ve not heard anyone else bitching, I don’t see that it’s one I need to address this week. @greenbuggy was kind enough to provide links to the required doodads should it irk me (or any of y’all) again.

If this is a unique issue in your experience, then chances are these guys are fine and I don’t need to void any warantees before moving on to the next roadblock.

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So far we have had no issues with the HX series since we switched to them, we switched soon after the first client had the flow meter issue, you are the second. We have the TX sensors stocked just in case the handful of those we have installed go bad. What’s interesting is the manufacturer was well aware of our application specs and it didn’t come up until it was an issue. I’ll make sure we stock a couple extra HX sensors so in the event it fails we can warranty it faster than the OEM.

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@tweedledew or anyone else running on demand hot water heaters; what brands and models are you using? and how hot are you running them?

time to build another still :wink:

11kw seems plenty.

Edit: I assumed “boost heater” meant I could set it hotter. but that does not appear to be the case. HX and JTX both have 90C limit.

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I used a Takagi T-H3 model 540. 199k btu, max temp 70c

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Im not sure if you know but most tankless hot water heaters adjust temperature accordingly to intake water temperature. It self regulates flow output from the inlet water temperature. Meaining the hotter the intake the less flow on output. Now the issuse is most tankless can only intake a certain temp. Mine was 92f. So to fix this I had a 55 gallon drum reservoir. I sticked a slump pump for flow towards the tankless. My output from the CLS was a hose positioned 6 inches away from the pump in width and the tip of the hose was a few inches to flush with the the the top of the slump pump. This position made my water have a steady hot/cold ratio that kept temperatures below the threshold of 92 throughout the recovery. If you deciderd to this make sure you use DI water or RO.

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I gonna go with “nope, didn’t know that” :wink:

I would expect them to adjust heat input (electrickery consumed) based on inlet temp, but without access to the pump I don’t see how they can throttle my flow.
Certainly none of the smaller ones I’ve used had valves capable or configured to control flow (yes, I understand how, but I’ve never seen the bits installed. Not sure I understand why they would be).

Devices to measure flow, yes.
Presumably designed to shut things down when adding
heat makes no sense.

I’ll keep the advice in mind. With the though that the first time I have a tankless heater refuse to behave, I’m gonna go looking for a flow limiter.

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I apologize I said that incorrectly. I’ll look up the tankless I had. It’s a regulating valve on the water inlet of the tankless… mine was a Manual screw adjustment. If the water was to hot than I had to restrict the flow by tightening the screw enabling the heating element to work. Eventually when 92f hit than I would no longer have enough psi for the tankless to work. This was of course due to tightening the screw restricting the flow. I figured the higher end tankless would automatically adjust instead of the manual screw. Eventually it will hit the point I had.

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And another thought. tankless hot water heaters weren’t designed for closed loop flow. Possibly higher end ones but they are meant for homes that recieved water from wells or local suppliers.

This is just a thought. Have a three way valve acuator before the inlet of the tankless. So one outlet runs towards the tanklesss. the second outlet from the acuator runs to the outer inlet of a shell and tube. The shell and tube runs to the CLS. The CLS outlet has a thermocouple. The thermocouple runs a master/slave to the acuactor. the thermocouple runs to the inside inlet of the shell and tube. The inside outlet shell and tube runs to the acuator. This way you keep a circular flow and only have to add heat when needed from the tankless. Seems a bit depth but I think it should work?

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Here is a PID since I’m horrible at writing sentences.

image
image3264×2448 1.55 MB

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new location, new toys.

next trick is a 1bbl conical fermenter => recovery still
for which I of course require heater.

this time I went looking specifically for a boost heater, one designed to give $)@!**&(&)@!_(*ing hot water for sanitizing dishes.

I’m going to give this one a try…

mainly because I can’t afford a hubbel right now.

It’s on the small side, but so is the 1bbl “still”.

I haven’t pushed go yet, and I’m open to other suggestions for a ~10kw tankless heater that will hit 180F.

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I guess if you can’t afford hubbel you won’t be able to hold this either but i know a vendor with closed loop water heater/circulators 12kw for around 2k and can go above 212 (depending on pressure your jacket tolerates)

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Sounds like the right tool.

You keeping their contact to yourself :cry:

:thinking:

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