Low flow switches

[Bob Rohr]

I'm working on finding a dependable . 5 gpm flow switch. The switch on the left started our working well after a few weeks it started sticking in the on position after the faucet was turned off. I replaced it with a new one, installed an isolation relay, same problem.

The one on the right, Harwil Q-12N is a different style switch, same .5 gpm. I installed it yesterday, I'll see if it holds up better.

 

[Fred61]

You think it's the switch as opposed to the water?

 

[goosegunner]

Bob,

How big of a buffer tank do you use for these setups?

How do you control the exchange of water from main storage as the main storage temps decrease towards the bottom end of usable temp?



gg

 

[Bob Rohr]

You think it's the switch as opposed to the water?

Good question. I have a cartridge filter and a softener upstream of the feed to the switch and HX. looks clean inside, a bit of red color from my iron water.

 

[Bob Rohr]

Bob,

How big of a buffer tank do you use for these setups?

How do you control the exchange of water from main storage as the main storage temps decrease towards the bottom end of usable temp?

Any size tank will work. I see some of the European set up with a 180L about 50 gallon tank. The more storage capacity the more DHW you can exchange. A 5 minute shower probably runs 10- 15 gallons of hot, depending how much cold I mix. I've seen this 160 gallon tank up to 167°F with five 4X8 collectors. Or it can be heated by the EKO up to 185° or so.

I have taken a shower with the tank down around 110°F. Full hot on the shower valve, but plenty warm. I should be able to get within 8- 10° of the tank temperature at the faucet.

The plate HX design shows

130° tank temperature
120° desired DHW
50° incoming from well
5 gpm flow rate

I know my summertime incoming runs higher than that, but actual use shows these calcs to be very accurate.

The only control mechanism is the flow switch to turn on the HX pump. I don't have a back up installed yet, so I'm the rest of the control, once it starts to run cool, I get out of the shower

I glance at the tank temperature before I try the shower. If it's below 110° I will not get a warm shower. I'm looking at a very small electric tankless, maybe 5-6 KW, with any pre-heat that should provide a shower without a problem.



gg

 

[goosegunner]

Bob,

I would like to run a buffer tank as a staging area for my DHW and forced air coil. My main 1000 gallons of storage is in the shed. I would like to have the buffer tank drop down to a certain temp and then kick on a circulator to bring hot water to the buffer, stopping when it is hot again.

The control confuses me, as my main storage depletes in temp.

Maybe I should just run my return from the forced air coil to the top of buffer tank, then return from the bottom of buffer tank to main storage. That way every time the furnace calls for heat the buffer tank will get some new hot water.

I typically burn when storage gets to +or- 140 so even at the bottom end I should get 120 or so in the buffer tank after forced air coil.

gg

 

[Bob Rohr]

Bob,

I would like to run a buffer tank as a staging area for my DHW and forced air coil. My main 1000 gallons of storage is in the shed. I would like to have the buffer tank drop down to a certain temp and then kick on a circulator to bring hot water to the buffer, stopping when it is hot again.

The control confuses me, as my main storage depletes in temp.

Maybe I should just run my return from the forced air coil to the top of buffer tank, then return from the bottom of buffer tank to main storage. That way every time the furnace calls for heat the buffer tank will get some new hot water.

I typically burn when storage gets to +or- 140 so even at the bottom end I should get 120 or so in the buffer tank after forced air coil.

gg

You can control that with a solar differential control. The control "watches" various sensor locations and switches on a relay output. The control I use has two differential functions, 2 relays, in one control.

The control turns on the boiler pump when the boiler is warmer than the tank, and a minimum of 140°F. A 3 way thermostatic valve/ pump controls return temperature to the boiler.

The second relay powers pump 2 to move energy from tank to tank. I set the high temperature at 180F. You can play around with temperatures, of course. These controls also have variable speed function, so the pump speed modulates based on temperature, which reduces pump on off cycling.

 

[Karl_northwind]

check out GEM flow switches. used for some of the instantaneous boiler water heaters.

karl

 

[goosegunner]

Thanks Bob! That control looks like what I may need.

gg

 

[goosegunner]

Just thinking about it a littl more. I already have a taco zone controller that controls my primary/secondary manifold circulators. Do they make a solar differential controller that will send a low voltage signal to my taco panel?

I don't think I would need the one with 120v outputs.

gg

 

[Bob Rohr]

Just thinking about it a littl more. I already have a taco zone controller that controls my primary/secondary manifold circulators. Do they make a solar differential controller that will send a low voltage signal to my taco panel?

I don't think I would need the one with 120v outputs.

gg

All of the newer style microprocessor base brands that I have experience with have a 120V output. Resol, Steca, tekmar, Watts, etc. This allows you to wire directly to the control without a relay or relay box. One less component to wire and consume power is eliminated.