How to prevent undesired water flow to indirect HW heater

Steve Garson_2

I have an Amtrol Boilermate with the heating loop controlled by a zone valve. With a 40* DeltaT, it needs more head, as I understand it.

I am going in to install a a Taco 007-F5-7IFC with integral flow check. I am guessing that for best performance, I should leave the zone valve open. But I presume that means that when any zone calls for heat, the water heater will get flow when it shouldn't. Due to lack of space, the circulator will be installed so the flow is toward the boiler, pulling from the water heater. My boiler control supports powering the new circulator as a priority zone,

Will the check valve in the Taco prevent the undesired flow when other zone call for heat? Should I be adding another check valve? Should I continue to use the present zone valve?

Thanks for your advice!

Steve in Denver

hot_rod

Whats the problem you are trying to solve? Faster recovery?  The coils inside those tanks lime up and performance drops over time

Steve Garson_2

Trying to have faster recovery so I can fill a bathtub, without pausing half-way through. Would liming of the coil cause the high delta-T of 40* ? If cleaning coil will do the trick, that would be good to know.

Jamie Hall

Scaling of the coil could indeed cause slower recovery. The high delta T suggests that that may be most of the problem. More flow from a bigger pump might indeed reduce the delta T, but that wouldn't mean you were getting more power into the Boilermate, and therefore wouldn't solve the problem.

If you did decide to go with a dedicated pump, you could perfectly well keep the zone valve operational, though, and control the pump with a relay and the zone valve end switch.

neilc

doesn't the 40* delta suggest there is decent exchange?

Big Ed_4

It looks like the indirect is piped to one of the zone valves hydronic loops ? If so ,adding a checked valve circulator would not help on heat migration to the indirect . I would check the guts of that zone valve .

What type boiler feed valve is that ?

Steve Garson_2

There is no heat migration today, since it has a dedicated zone valve. I am just anticipating that possible issue if I install a circulator and leave the zone valve open. Caleffi feed valve.

Jamie Hall

neilc said:

doesn't the 40* delta suggest there is decent exchange?

Yup

Big Ed_4

It you leave the zone valve open to the hot water heater , any other zone call will also charge the tank...

I noticed a mixing valve ....

What seems to be the problem ?

EBEBRATT-Ed

@Steve Garson-2. From your other post we determined that the circ is the right size. You need to find out why you have a 40 degree TD. Is it the boiler mate or is it the heating system. Run them one at a time and together and see what you get. That will point us in the right direction.

hot_rod

Assuming you have a 4 gpm flow through the piping
500 x 4 x 40 is 80,000 btu being added to the tank

Is the 40 delta when the tank is cold and that zone flowing ?

40 delta with no flow = 0

How hot do you keep the tank?

Steve Garson_2

The 40* delta is when the tank has been depleted by the bathtub fill and the boiler water has been circulating since shortly after the start of the bathtub fill. I keep the tank at 140*.

Big Ed_4

You are fixated on the 40*delta . To me it is too high..

Hot water is the highest load in a family filled load . I would always use an independent circulator and the latest piping to an indirect . The idea is pumping all you can from the boiler to that tank .

Joe Mattiello

DHW heating should 20 degrees delta T max. If you’re not able to maintain 20 degrees, your pump is not sized properly. Keep in mind, boiler has to be sized for total system load too. 

Some find priority feature on Zone Vavle control beneficial when boiler can’t keep up with DHW heating load. Every system is unique. 

For additional support contact Taco at (401) 942-8000 

neilc

wait a minute,
what is the temp at the boiler?
you're not running OA resest, are you?

Steve Garson_2

Boiler is set at 190*

Steve Garson_2

To bring this back to the original question: If the water heater has its own circulator with integral flow check, how do I prevent unwanted circulation from the boiler without the present zone valve. Or will the integral flow check do the job as it is.

hot_rod

Yes a circ with a check will be adequate. Even if you got a small thermal conduction it would just raise the tank temperature.

40 gallons is not a lot of DHW if you fill a tub. You could increase the tank temperature and add a mix valve. That would give you more draw down for tub filling.

I suspect the delta is high, when there is 50 degree incoming water hitting the coil. I’ll bet the delta closed as the tank heats up. Measure it when the tank is near setpoint.

The delta changes as the temperature in the tank changes, not to worry about that. If it were limited to a 20 delta. 500 x 4 x 20= 40,000 btu/ hr is being transferred to the tank cast iron boilers can handle 40 delta, especially with a 190 SWT.

At some point the 3/4 copper becomes the limiting factor in how many gpm you can shove into the tank. The Amtrol spec sheet probably shows performance at various flows and SWT

Slow recovery is an indication of a scaled coil, usually indicated by a tight delta

1” piping would allow you to pump 8-10 gpm, that would make a huge improvement. Assuming you have 120 k of boiler or larger

hot_rod

No harm in doing a descale procedure

https://www.google.com/search?q=amtrol+boilermate&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari#fpstate=ive&vld=cid:4af7e1fb,vid:rqzZ7tJFtZs,st:0

Steve Garson_2

Recovery takes just five minutes. So perhaps should I just leave things as is?

hot_rod

Steve Garson_2 said:

Recovery takes just five minutes. So perhaps should I just leave things as is?

So the initial dump load for a tub fill is the issue? Then a larger tank or increase the tank storage temperature
Increase the tank to 150, mix down to 120. That would get you another 12 gallons or so on the first dump.

Steve Garson_2

thanks,  that sounds like an easy fix

EBEBRATT-Ed

I still say a 40 degree delta is not good for the boiler.

You zone with pumps or you zone with circulators. I doubt you want to buy pumps for all your zones so stick with the zone valves. Or you can use a separate circ for the indirect and the existing circ for your zones.

But to me that is overkill. You have enough pump to do the job. Also check the model of the zone valves so we can check the CV. They could be undersized.

I still think you need to find where the 40 degree delta is. Is it the indirect or the heating system?

hot_rod

looks like you have a DHW mixing valve, so setting the tank temperature up is a simple way to get more DHW. You could probably run down to 110 or 105 to fill a tub.
this assumes 55° incoming, 120 mixed.
Lochinvar "tool kit" has this free online simulator.

For a 3 way thermostatic valve to mix accurately, the hot supply should be at least 25° higher than the mixed outlet. So cranking the tank to 150 helps the mix valve respond.

Steve Garson_2

Hot Rod, thanks! Just raised the temp. You've offered very constructive advice to me over many years.

hot_rod

Truth be known many indirect manufacturers run that wide 40∆ to assure the tank can get full boiler output when they test them and create their output charts.
But it requires a 190F SWT. They also do their standby loss calculation in an 85° room

The other option is 1" pipe and run a 20∆, or smaller, to assure you get full boiler HP to the job.

Personal preference, some installers like to series pipe the indirect and give it it's own circ. That too assures plenty of flow.

Amtrol instructions seem to recommend a dedicated circ.
Or full port zone valves, which I don't think you have.

At days end I think what you have is adequate without repiping for a small % increase. Crank it to 150- 155°

clammy

Your only gonna get so much out of a tank period . If it is not cutting it w a mixing valve and tank temp still drop and having the tank set at all higher then needed temp and mixing down . I would look at narrowing the aquastat differential setting at bit lower activating the boiler Sooners . Personally I usually always use a pump for indirects over zone valves . Possibly your tank may not be sized for your demand . Possibly a coil limiter installers in your hot water outlet to limit flow . If you go to your tub and take a 5 gallon bucket and see how many seconds it take so to fill ,the answer will Ben right there fill a bucket in 15 seconds well then your trying to do something like 20 gallons a minute for your fill ,gonna need bigger storage then a amtrol indirect .
I once ran into this issue w a home owner who wanted 160 at her giant soaking tube nobody could make her happy . I did at then time flat plates where not widely used so I added a zone valve in parcel w the amtrol ,took the dedicated Hot water line to the tub and ran it through a hot plate and there’s you go ,had another mixing valve set for 160 on the plate so outlet . As much as the indirect tanks temp dropped that’s flat plate would kick it up . It was only a small sweps 3/4 plate but she was happy as a clam . The other side of the coin is at best you’re throwing 4 Gallon per minute at that’s tank and isn’t it set on priority ?
In my experience I’ve yet to see a small indirect fill a large hot tub and remain piping hot . And please remember the higher the temp setting on the indirect the faster it will lime up . If adding a pump I would get rid of the zone valve and pipe it correctly possible increase your s and r to the tank Peace and good luck