Aquastat Alternative?

[WoodNotOil]

Does anyone have a working alternative to using a Honeywell Aquastat? I need something that will sense the temperature and at a set temp charge a DPDT relay. I will have 24vac available for current for such a device. Links to components would be great too. Thanks.

 

[Nofossil]

I don't have links, but I've used snap-action temperature switches for exactly what you're talking about. They're a few bucks apiece, come in both NO and NC, and are available with different temperature setpoints. Downsides: they're not adjustable, not particularly accurate, and the hysteresis is fairly large and also not adjustable. I think Digikey carries them.

You may also be able to use electric hot water heater controls. They are adjustable and have an aluminum backplate that would need to be held against the heat source.

 

[BrownianHeatingTech]

You can just attach a relay to an aquastat. I've done that, when I needed more than SPDT.

Joe

 

[pybyr]

some of the PLC type devices seem surprisingly affordable and remarkably configurable - do a search on here for the "coldfusion" one that some people have mentioned.

I know that it (the coldfusion one sold on ebay) is very popular and has been used with good success among the folks who convert beckett burners to run on used cooking oil -- where there's a need to precisely monitor and control the temp of the veg oil that's being preheated in order to reach good flow/ flash point characteristics.

automation direct's web site also seems to have tons of different stuff that I haven't even been able to wade into yet- but intend to as I eventually get to planning details of my controls

by the way, WoodNotOil, have you gotten to the bottom of your thermosiphoning issues, and if so, what have you pegged as a cause, and as a good solution?

 

[Dune]

What is wrong with a honeywell aquastat? There are different models available. I think I paid $80 for a brand new one from the plumbing supply.

 

[pybyr]

What is wrong with a honeywell aquastat? There are different models available. I think I paid $80 for a brand new one from the plumbing supply.

nothing in particular wrong with them, for what they are, and if they do what you need off the shelf

but some of the PLCs are way more accurate, way more configurable and adaptable, and surprisingly, sometimes less expensive than the Honeywell type electromechanical controls

 

[Dune]

Oh.

 

[WoodNotOil]

Thanks guys. I will check out your suggestions.

My question was simply wondering if there was a less expensive and possibly more accurate way to do this. In some applications, the Honeywells seem to me to be overkill. However, I have no problem with using them.

Pybyr - I am going to put in a Taco EBV that will open only when pumps go on. For now I just close my ball valve. The real temp issue was with the copper well I was using for the tank bottom sensor. The whole length was heating and causing the reading to be much higher. I put the sensor on the bottom line outside of the tank (foil wrapped and pipe insulation) and when the charging pump is on, I get a more accurate reading. Stratification is now equal to my delta T through the plate on the tank side, about 20*. Most likely, since I am not drawing from the tank in the summer, that stratification improves as DHW runs through the coil over the days between burns.

I am quite pleased with the overall tank at this point. It works well and will have a start to finish price tag under $1500. That may be a record for 1000 gallons on here.

 

[herbert]

I have to get aquastats for my swimming pool and spa exchangers---- the company i am dealing with offer both electric and mecanical aquastat----is either one better than the other ?

 

[WoodNotOil]

Nofossil - Is this what you were talking about: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=317-1019-ND Spec Sheet: (broken link removed)

I need something like an aquastat on the line going to my flat plate hx from the boilers so that the tank charging pump won't come on unless there is sufficient heat to charge with. When zones are calling for heat there may not be enough heat for charging for example. Would one of these work in place of an aquastat? I understand that I can't change the temp setting. Are they able to take a pretty constant 175* temp or will it breakdown over time? It says it is rated at 120vac 3amp. Can I run the 120vac going to the pump through it just fine? If so, I think I might try it. It is only $8.52 and I can always replace it pretty easily with an aquastat if it doesn't work/last. Thoughts?

 

[Nofossil]

Nofossil - Is this what you were talking about: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=317-1019-ND Spec Sheet: (broken link removed)

I need something like an aquastat on the line going to my flat plate hx from the boilers so that the tank charging pump won't come on unless there is sufficient heat to charge with. When zones are calling for heat there may not be enough heat for charging for example. Would one of these work in place of an aquastat? I understand that I can't change the temp setting. Are they able to take a pretty constant 175* temp or will it breakdown over time? It says it is rated at 120vac 3amp. Can I run the 120vac going to the pump through it just fine? If so, I think I might try it. It is only $8.52 and I can always replace it pretty easily with an aquastat if it doesn't work/last. Thoughts?

That's one of the packages that they come in. There's also another that I photographed for a sensor thread recently. They're rated for enough current to drive a circulator, but I've only used them to switch relays and such. The big disadvantage is that you can't adjust the deadband - the difference between the on and off temperatures.

Back before my wood boiler and controller, I built a heat scavenging circuit for recovering leftover heat from my oil boiler to heat the hot tub. The only components I used were these temperature switches and relays.

 

[WoodNotOil]

Thanks Nofossil. Just to make sure I have it right, NO would be open when below the set temperature and close when it hit the temp the switch was designed at(158* in this case)? Just want to make sure I get the right one.

 

[Nofossil]

Thanks Nofossil. Just to make sure I have it right, NO would be open when below the set temperature and close when it hit the temp the switch was designed at(158* in this case)? Just want to make sure I get the right one.

You got it. Don't be under the illusion that it will be 158 degrees, though. It will be withing a couple of degrees of that, but they're not precision devices. They are designed typically for overheat protection.

I used them in part because I get a kick out of using something constructively in a way that's different than intended. Also because I'm a cheapskate.