indirect control setup

Tim Potter

Well, I have made the latest upgrade to my system,

1) Replaced the failing a-stat in my Amtrol WHS-80 boiler Mate with a Johnson control A419

<a href="http://cgproducts.johnsoncontrols.com/MET_PDF/125188.PDF">http://cgproducts.johnsoncontrols.com/MET_PDF/125188.PDF</a>



2) Added a Honeywell AMX101 Mixing Valve

<a href="http://www.forwardthinking.honeywell.com/related_links/water/mixing_valve/sell/63-9370.pdf">http://www.forwardthinking.honeywell.com/related_links/water/mixing_valve/sell/63-9370.pdf</a>



Now I am looking for advice on how to setup the Controls.

I presently have the AMX101 mixing down to 120*

The Aquasmart control on boiler NOW is set to high limit 190* with a 45* diff.

Heating is done with full ODR Injection control with Radiant Tube in Concrete (lower level bedrooms) & tube in Gyp (Main floor rooms)

Boiler: Slant-Fin SX-150 @ 9100’ altitude. Mark Eatherton has measured the gas meter and reports 99,000 btu gas flow.

Taco 007 dedicated to the indirect.

A419 Set point to 140* with a differential of 10*



My questions arise from observation of the heating cycle for the Indirect. This is our Mountain vacation home. We drained & cleaned the hot tub, wanted to use it that night, so I hooked up the hose the the washer hot tap & filled it with hot water from the indirect.

There was no call for heat, only for hot water.

It took several tanks of water to make up that much water for the hot tub. While observing the reheat cycles, I noticed that when the Indirect tank temps were low (say under 100) the boiler temp would rise slowly & mostly stay in step with the indirect. At some point the boiler temps started to shoot up quicker than the indirect & the Boiler would cut out on high limit (190*), the pump would keep running, and the boiler would cut back in @ 145* (45* dif)and then make a run for the top again. That is when I raised the HL to 190 from 180 & maxed the diff out to limit short cycling. It stabilizes to about 6 min on, & 6 min off (HL cutout) until the indirect is satisfied.

It seems like the indirect should be able to transfer the heat better to the water tank than 6 min on, 6 min off. I never paid attention to the heating prior to the latest upgrades, mainly because You could not see the temps inside the indirect with the factory control, & I had the indirect set to 120* (or so I thought, I never measured the temps)



Thank You for your help



Tim



PS Mark, no bears in WP recently, enough rain & food in the mtns i guess

Mark Eatherton

Controls and bears....

Tim, I was looking at my Service and Choke cherry bushes by my cabin, and the fruit looks pretty meager due to the drought earlier this summer, meaning the bears are going to be aggressive looking for food this fall... Something I'm not looking forward to.



Regards you water heater, all manufacturers give a btu H rating for thier appliance, and it is rated for BEST case scenario. Best case is a cold tank and a hot boiler. Under that scenario, you tank will pass a BUNCH of btu's to the potable water. BUt when the tank starts getting warmer, the differential temperature between the source and the load gets so low that a lot less btu's are transferred near the end of the cycle, hence bouncing off of the high limit. This is why I prefer a reverse indirect over a conventional indirect. Much larger surface areas to transfer heat, and a lot more water for storing the heat.



Additionally, if the coil in your tank is getting limed up, it too will retard the flow of heat from the boiler water to the potable water.



With your set up, IF you were to go with an RI, you'd need to put an anti condensing valve in the circuit of the boiler to avoid drawing it too low during peak loading conditions.



The next time you have to drain and refill your tub, instead of exhausting the tank, set the flow rate such that you get roughly a 60 degree rise across the system as a whole on the potable side.



The math is, 99,000 * .82 = 81,180



81,180/8.33/60/60 = 2.7 GPM. So, set the hot water fill hose to fill a 5 gallon bucket roughly half full in one minute, and the boiler should start, and stay on until you shut off the flow of water and it tops off the storage tank. That is the most efficient mode of operation for your system.



If memory serves me correctly, the water in WP is not too hard, but if it has changed, you might want to consider an electronic water conditioner to keep the HXer clean.



See you this Fall? Should be a colorful Fall.



ME

Tim Potter

Indirects & Bears

Thanks for the input Mark, I'll keep an eye on the reheat cycles, & great tip on the hot tub filling at a low pace.



My wife was out in WP a couple of years ago without me. She was sitting on the deck, looked up on the roof, and there was a huge pile sitting on the roof. Not really sure what she was looking at, she called the people who check on the house when we aren't there & do the snow plowing. Jimmy came right over, took 1 look, @ said "Thats BEAR dung mam", my wife about left her own dung after hearing that. The theory was something bigger than him chased him up there, we found the claw marks on the front porch columns. She never goes out on the deck without looking back up at the roof now.....



Planning on late Sept visit, we would love to see your spot if the days & dates work out



Take Care,



Tim