Best settings for DHW indirect water heater with Lochinvar Boiler?

kalex1114

Hello. I'm back

Made few changes to my setup and looking for suggestions on best settings to use.
Refresher on my setup:
Lochinvar KHN-110 with Bradford White SW-2-65-L Powerstor Single Wall Indirect water heater.

I just changed 2 things on my setup:
1) Installed a Honeywell AM-1 mixing valve


2) Replaced Honeywell Aquastat with Lochinvar Tank sensor.

As you can see (circled in red) location of the sensor is toward the bottom of the tank and top of the tank is hotter.

What I'm looking for is suggestions on what to set new values on my lochinvar
Here is what I have set so far.
DHW boiler temp is set to 187 with 3 degree offset (this setting works best to prevent my lochinvar getting blocked as 180f doesn't work. DHW Boiler Diffirential 10f.
I can also set it to 175 with 10f offset but I went with 187.
Question - for faster heatup of my indirect model is it better to run it at 187 degrees or lower it to 175 for better and faster absorption of BTU inside the tank?

Now on to the tank temperature side:
I have it set currently to:
Tank Setpoint: 135
Tank SP differential: 6f
Tank Min setpoint : 60f
Tank Max Setpoint: 140f




I noticed that when DHW call is satisfied my tank temp slowly creeps up to around 150-154 degrees over next 30 minutes to an hour.
Here is a picture of the temp now:



So because of sensor location (bottom of the tank) and around 15-20 degree creep up I'm thinking of lowering the tank temp to 125-130. and maybe bringing up differential to around 10f instead of 6.
What settings would you recommend I try? Those that are running Lochinvars currently

Thank you

Alex

hot_rod

One thing to keep in mind is bacteria, legionella prevention. Keeping the entire tank above 140F assures the bacteria cannot get a hold in the tank. if things like that concern you

Since you have a thermostatic mix valve to protect the distribution temperature, I'd leave the tank as you have it.

The tank will stratify as you have noted and have a higher temperature up top.

The hotter the boiler SWT, the faster the recovery.

What about the pump size and speed? The higher the flow rate the faster the recovery also.

Is it performing to you needs and expectations?

kalex1114

Thank you Hot Rod. I have a 3 speed pump on it and its running at fastest speed. Its performing fine. I just wanted to make sure its ok to keep tank at these temps and that they are not too high where it can have negative impact on the tank.
Also want to make sure that its as efficient and has fastest recovery possible. As during recovery time, heating is not active

hot_rod

My opinions to keep the tank at 140 at the stat location, knowing that it is sufficient for anti legionella.

Also thermostatic valves really want around a 25° higher temperature hot side compared to mixed outlet to perform accurately.

If ever you add a constantly operating recirc pump, the tank would mix, and not stratify as you see now.

What I do believe that elevating tank temperature diminish the life expectancy. The higher the temperature the more the mineral precipitation. And of course a bit more jacket loss at higher operating temperatures, and fuel cost.

DHW is a tough question that comes across hear as so many different ideas on how much they need or want, and how quickly.

kalex1114

According to the Honeywell AM-1 manual Minimum required temperature difference between hot
and mix 3° F (1.5° C).

kalex1114

I adjusted tank temp to 130 and after coasting tank is at 147. Seems ok. Dhw heating cycle ended up being about 40 minutes taking tank from 123f to 130f. Then it coasted up to 147 with no usage. I might lower differential from 6f to 3f for after recovery time

hot_rod

kalex1114 said:

According to the Honeywell AM-1 manual Minimum required temperature difference between hot
and mix 3° F (1.5° C).

A suspicious number to me, most valves show 25- 27°. Caleffi and Taco for 2 examples.

Without indicating how they come up with that number they can call it whatever they want I suppose

We say 27° for STABLE operation. Certainly the valve still operates at lower differential but temperature accuracy will be less.

The listing number like ASSE 1070 requires the valve be accurate across it range within several degrees plus or minus. If they can pass that test at those conditions, so be it.
Our product manager recently witnessed that test on some new valves we listed. Valves occasionally do not pass that stringent test requirement.

Putting the valve on a test bench would be a sure way to confirm the claims.

NY_Rob

A 3 deg differential is really tight... someone washes a coffee cup and your boiler will fire up. It could create excess cycling and short cycles.

kalex1114

That might be. After coasting temp is at 147 which is 27 difference. Mixing valve is set to 120f. Temp gauge and temp strip on the pipes seems to match closely

kalex1114

> @NY_Rob said:
> A 3 deg differential is really tight... someone washes a coffee cup and your boiler will fire up. It could create excess cycling and short cycles.

It’s actually more since after coasting with 6 degree differential boiler shoots up another 15 degrees. So lowering tank differential should be ok. I lowered it to 5 for now