DHW HX tie in

[timberbuilt]

I am in the process of trying to hook in a plate heat exchanger to my electric DHW heater. The instructions/drawings don't show much and I am a little confused on the best approach to take. The drawing shows the cold water in one side of the HX and the hotwater from the boiler on the other side. Simple as that right? Well it seems like if you only did it that way all you would really be doing is heating the water going into the tank instead of continuously heating the water in the tank, so if you were not drawing DHW the electric elements would be doing all the work to heat the tank? Am I missing something here? I was thinking that I may want to put a mixing valve on the DHW-out so the tank would circulate but how does the tank actually circulate through the plate? Convection? Did I screw up and should have got a sidearm?

And where should I put my aquastat to control the pump pushing the boiler water through the HX? I was thinking on the bottom of the DHW tank? It is the external type so I was thinking inside the tank insulation taped to the sidewall of the DHW tank.

Anyways any advice would be great.
Thanks

 

[Rick Stanley]

Not a pro here by any stretch and there are pros here that will tell you for sure, but maybe you need another pump to circulate the drinking water side and then turn off the juice to the elements.

 

[varna]

timberbuilt,
I put my HX on the HWH "out" line and piped it to the boiler exactly the same way. This way, when you turn on the hot water (faucet) you get instant hot water....all day. The original HWH becomes a storage tank of....cold water. I see no reason to heat that water going in and yes.....if not used it will cool.

BTW I did have to install a "tempering" valve because if not my water became too hot... When my boiler is shut down, all I have to do is fire my HWH back up and everything works the same.

 

[markmudd]

You would need to circulate it to keep the 40 gal or so hot. If the flat plate exchanger can supply continuous hot water for all your needs, in therory you would not need to circulate, and hot water heater sits there and is cold water

 

[timberbuilt]

I'm thinking I screwed up and should have got a sidearm. Thanks for the good advice guys. Varna and mocus: can your plate exchangers keep up with your hot water demands independent of a hotwater tank?

Idealy I would like to have it so my Hx would keep the hotwater tank at say 150 degs while my elec was set at like 140 deg. That way as long as my boiler was going I'd be hx-ing but if it wasn't the elec hotwater elements would kick in. Is there anyone that has plumbed in a plate exchanger to accomplish this using convection or ? on the drinking water side? Or am I condemned to plumbing in two pumps?

On the same subject I would like to control this configuration from my Taco 506 control box. Is there such a thing as low voltage (24 volt) aquastats? The 506 takes low voltage thermostats coming in and 120 volts going out. I've got a regular aquastat from Honeywell I could use but I would have to wire it direct to my pumps but going through the 506 control box would make my main circ pump operate.

 

[bigburner]

Put a pump on both sides, we have needed to do this with side arms also- Here's the deal! Side arm works on convection and in order for convection to work really well you need a large temp difference {split, delta -t, what you want to call it} Most people try to keep the temps low as possible and still heat the house. If you have a long time between uses [no pump] the side will provides decent DHW, but it won't do heavy use with out very hot boiler water. The plate HX is a great product I have never ever had an issue with these. [may be just lucky] DHW is the biggest challenge in this whole process. Use the Plate Hx put a Taco 006 or similar on the domestic side, Ya don't need to run it threw the controller, if that model has a DHW priority zone just you could do that and dump the other loads.

 

[ewdudley]

On the same subject I would like to control this configuration from my Taco 506 control box. Is there such a thing as low voltage (24 volt) aquastats? The 506 takes low voltage thermostats coming in and 120 volts going out. I've got a regular aquastat from Honeywell I could use but I would have to wire it direct to my pumps but going through the 506 control box would make my main circ pump operate.

The 506 inputs are supplied with 24VAC from the 506 itself so all you need is a switch to activate the zone output. Any aquastat that controls a NO contact will do the trick, a RANCO ETC 111000 or equivalent.

But if you've already got a Honeywell aquastat kicking around, most Honeywell aquastats can be used as simple temperature controlled switches by permanently disconnecting power inputs (L1,L2) to the unit, permanently disconnecting the internal wiring to the internal mechanical aquastat, and then wiring your external switched-function directly to the internal mechanical aquastat terminals.

I'm thinking I screwed up and should have got a sidearm. Thanks for the good advice guys. Varna and mocus: can your plate exchangers keep up with your hot water demands independent of a hotwater tank?

Idealy I would like to have it so my Hx would keep the hotwater tank at say 150 degs while my elec was set at like 140 deg. That way as long as my boiler was going I'd be hx-ing but if it wasn't the elec hotwater elements would kick in. Is there anyone that has plumbed in a plate exchanger to accomplish this using convection or ? on the drinking water side? Or am I condemned to plumbing in two pumps?

If you're lucky enough to have a situation that would make it possible, you could place the DHW heater somewhere upstairs from the HX and then plumb it in the same as a sidearm with the HX above storage and the tank above the HX. Then the HX would be fed by gravity as would the DHW tank. Look Ma, no pumps.

--ewd

 

[timberbuilt]

What if I just put a transformer 120 to 24 volt transformer on the output of the aquastat?

 

[ewdudley]

What if I just put a transformer 120 to 24 volt transformer on the output of the aquastat?

Have a look at the 506 schematic and you'll see that it supplies its own 24VAC. You don't supply 24VAC to the 506 to turn a zone on. It supplies its own 24VAC and you supply a switch to turn the relay coil on using the 506's own 24VAC.

The two terminals for any give zone on the 506 are used to activate the relay coil for that zone.

To activate the coil one of the upper terminals need to be connected to the other upper terminal through a switch.

You can't feed an external 24VAC source into the relay coil of the 506 without a lot of monkeying around to get the common of the external 24VAC referenced to the common of the 506 24VAC. It would probably be a lot simpler just to supply the switch closure it's looking for.

--ewd

 

[varna]

I'm thinking I screwed up and should have got a sidearm. Thanks for the good advice guys. Varna and mocus: can your plate exchangers keep up with your hot water demands independent of a hotwater tank?

Yes, I have all the hot water I need..... 2 dish washers, 2 clothes washers, 2 showers.....I understand that you want to keep your tank water hot "in case" your boiler goes out. My question is, how long would it take to get your tank hot when you turn it on? I have a propane HWH that I leave off. If I needed hot water due to my boiler off or a problem, waiting to heat my tank doesn't seem like a long time to me. Just seems like a lot of "grief" trying to keep your water in the tank hot for a "maybe". I have had this for 2 winters now and have had no issues.....also, from what I have read, a side arm doesn't do well with heavy hot water loads......a plate HX constantly heats when you call for hot water.

 

[timberbuilt]

OK, I got my Rancho ETC in the mail and now I have to figure out how to hook it up to the 506 Zone control. I'm not quite following what "No Contact" means? I think I wire the 120v into the upper connections then run from "NO" and "C" on the lower connections to the 506?

 

[ewdudley]

OK, I got my Rancho ETC in the mail and now I have to figure out how to hook it up to the 506 Zone control. I'm not quite following what "No Contact" means? I think I wire the 120v into the upper connections then run from "NO" and "C" on the lower connections to the 506?

"No Contact" means just what the Order of Protection says it means: No phone calls, no texting, no tweeting, no letters 'trying to make her understand', no hanging around the produce isle hoping to bump shopping carts. It's over dude, time to move on.

Oh, you mean in the context of an output relay on a temperature control?

Yep, you've got it right, it's the normally open contacts that you're going to use to activate the zone relay on the 505 by connecting the common (C) and normally open (NO) terminal to a one of the pairs of terminals at the top of the 506.

In heating (H1) mode the 111000 will close the NO contacts when the sensed temperature falls below the setpoint (S1) temperature minus hysteresis (DIFF1). The NO contacts will open back up again as the temperature rises back above setpoint (S1).

Cheers --ewd


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