Heat Dump Wiring?

[PXR]

Hello all, I have been an avid reader of posts here and have learned a lot. Thank you. This is my first post - a question.

I recently installed a Varmebaronen 40 UB natural draft wood boiler in my basement. I have 500 gallons of thermal storage which is connected to a single zone. I have primary/secondary circulation loops powered by a Taco SR503 Switching relay. The system is simple. Thermostat calls for heat, SR503 powers the primary and secondary circulators. House gets warm. The system is running great thanks to Dean from Smokeless Heat!

While I will get better at judging how much wood to fire and not boil the system over, I would like to add a simple heat dump by adding a strap on aquastat. After reading related post I am not sure best how to wire this in. Can I simply bring 24v power to an aquastat set with 210F low limit to the thermostat terminals already in use for the first zone on the switching relay so that either the thermostat or the aquastat could switch on the pumps. Which type of aquastat do you recommend? Any help would be greatly appreciated.

 

[maple1]

Hey - nice boiler.

You should have a dumping setup that will also work when the power goes out. Trust me, that boiler will heat up quick if the lights go out in the middle of a hot burn. So - how is your convective flow to storage from the boiler? If things are set up good (elevated storage, short piping), you can try to take advantage of that and it would impact how you want the dumping setup to be done. With mine, I have a normally open zone valve on one of my top boiler fittings, that is plumbed into my regular upstairs baseboard zones downstream of the normal zone valves for them. When the power goes out, that valve opens so boiler flow can convect to those zones if I'm burning. That is in addition to what would also convect to storage through the loading unit circuit - I don't think I have quite enough storage elevation to take all the heat. And, for a power-on overheat situation, the power to that NO zone valve first goes through a break-on-rise aquastat (think it is an L6081 but not sure) that will break the circuit to the zone valve if the boiler gets up to setpoint (too hot) thereby letting heat dump past the NO zone valve - and the stat also starts my load circ pump.

For even more redundancy, I added a 2200va UPS to my loading unit that I found on kijiji so it can function as normal if the power goes out while burning.

I use a Johnson A419 controller to control my DHW setup - I think it would also make a good controller for dumping heat, you could surface mount the probe on top of the boiler against a fitting or something and it is fully programmable with different functions (can work as either make on rise or break on rise). Plus it has a digital temp display. You could likely use that to start your pumps - but the pumps won't run if the power goes out. Do you have something in place for a power-out heat dump? Will storage handle that?

 

[PXR]

Thanks Maple1. The height difference between top of boiler and tanks is probably no where near enough to thermosyphon off the btus of a good fire if the power goes down. I can unscrew the flow check valve after the circulators to allow for natural circulation if power goes down- but that is hardly a fail safe. My plan for power outages is a generator connected to an outdoor disconnect. As it is set up now, it requires me to go outside, throw a switch off the meter base and start the generator. It works, but I need to be home.

I am really just starting to get a feel for the the system and have just finished adding insulation to the tanks and pipes in the last week, and the weather is just now dropping below O celcius. I have been trying to get the tanks pretty hot - 95 - 100 celcius so that I can go for 8 -10 hours without a feed. I am starting to think I did not install a large enough system. (I am going to do more to prevent heat loss in this drafty 3000 sqft 1860's farmhouse too). I am running a Jotul F500 wood stove too.

I will look into the A419, but you are correct. I should have a better power-out plan too.

 

[maple1]

Yes, you would benefit from more storage. Your boiler is likely up to the task.

We have a 20 year old 2700 sq. ft. 2 storey on an open hilltop. Depending on the day & how cold it is out, I burn between 6 & 12 hours per day in the winter. Usually light about now, and done burning when we go to bed. On the longer coldest days I start a bit earlier & put some wood in on the way to bed. I would like to have more than the 660 gallons I have now, but think I'm at my space limit for it. I do a few things to get the most coasting time I can - I heat the house up a bit warmer than normal when burning, and set back a couple of degrees on some of our zones when not burning.