3-Way Mixing Valve on an outdoor gasifier?

[WoodChoppa]

All these discussions about 3-way mixing valves on the indoor gasifiers has got me thinking I may be missing out on some perfromance. I've got an Empyre Pro 200 gasifier sitting in my backyard and i'm just wondering how I could go about hooking one of these Danfoss valves into my system to sustain a 150 degree return. I've never heard of a short return loop plumbed on any outdoor boiler because it would probably freeze solid! Any point to having a valve like that sitting in the house 70 feet away? Any suggestions?

Thanks.

 

[Duetech]

Insulated pipes with constant flow will not freeze. Energy trade off (wood vs electricity) is the difference. I believe the danfoss can be set to have some flow regardless of whether there is a heat demand or not.

 

[ewdudley]

All these discussions about 3-way mixing valves on the indoor gasifiers has got me thinking I may be missing out on some perfromance. I've got an Empyre Pro 200 gasifier sitting in my backyard and i'm just wondering how I could go about hooking one of these Danfoss valves into my system to sustain a 150 degree return.

The main reason for return protection is to prevent corrosive condensation on the inside of the boiler. Plus I suspect it helps some boilers to burn better if everything is good and hot, but I don't have a good explanation as to why this would be true.

It's possible your Empyre Pro can keep its interior surfaces hot without any special way of controlling return temperature.

First, as an unpressurized system, the boiler is typically connected to systems through a plate HX of a water-to-air HX, so return temperature will tend to be plenty hot to begin with.

Second it looks like they bring return water into the system fairly high on the water jacket. This would let the return water mix with the hot water before falling to the bottom of the boiler, and I would assume they disable any load circs when the water jacket starts to get too cool, long before there's any danger of condensation on the interior.

And it definitely helps that the Empyres have a lot of water in their water jackets, so there's plenty of hot water for cool mix with, which makes it easy for the controller to figure out that the flow of return water needs to be stopped before water jacket gets too cool.

Maybe poke around with an IR gun, I'll bet you'd find that the water jacket is all hot all the time.

Cheers --ewd

 

[Hunderliggur]

ewd's response makes sense. If you find you do need return protection you can put the Danfoss in the house. Just pretend you are near the boiler with the bypass and valves. The mixed return will be 140F minus line loss which should be minimal. Why does is appear to burn more consistently with higher temps? I don't know.

 

[Fred61]

I experienced the cold burn phenomenon a few years ago. I had a wood stove that I added an internal coil to with limited success. To supplement that I kept adding coils to the exterior of the stove to pick up the radiant until I had three sides of it completely covered with coils. The stove all but lost it's ability to maintain a fire. It burned so dirty it plugged the chimney cap with creosote and needed to be cleaned almost on a weekly bases and you can imagine every other surface was also carboned up. You really need to burn your fire as hot as you can. Isn't that why they isolate the fire from the water jacket with refractory bricks?
I need to light a new fire every day with my EKO because of my heat load. Until the boiler is up to temperature, my fire is not ideal.

 

[WoodChoppa]

Thanks all. I think Fred 61 nailed my understanding of the issue. On startup the refractory mass and the water mass need a lot of charging to get up to the temperatures needed for a clean efficient burn, which explains why any boiler will smoke for the first 15-20 minutes from cold start. I think the Danfoss gives the boiler a headstart to reaching these temperatures by ignoring the demands of the load and serving the demands of the boiler first.

I like the idea of putting the 3-way in the house and will give that a try to see what happens.

 

[goosegunner]

Be careful about letting the boiler drop below Danfoss temps if you are running more than one pump.

I had my primary load pump running continuous last year. If the boiler ran low on wood the primary manifold would dead end because the Danfoss effectively stopped the cool return flow through the boiler. This year it is not an issue because I am running storage and the water will draw and return through the tank.

gg

 

[ewdudley]

On startup the refractory mass and the water mass need a lot of charging to get up to the temperatures needed for a clean efficient burn, which explains why any boiler will smoke for the first 15-20 minutes from cold start. I think the Danfoss gives the boiler a headstart to reaching these temperatures by ignoring the demands of the load and serving the demands of the boiler first.

I've never known there was such a thing as a boiler that will permit a load circulator to run until the boiler was up to its low limit temperature. The purpose of the low limit is to ignore the demands of the load and to serve the demands of the boiler first. Does the Empyre Pro not have a low limit aquastat?

 

[goosegunner]

Might be a carry over from the OWB days. My Taylor OWB boiler only had a high limit aqua-stat. The pump was independent of the boiler controls. Maybe the empire is set up like that.

gg

 

[ISeeDeadBTUs]

I can't comment on the mixing valve . . . I don't use one. I try to have only one 'cold-start' each year, so I don't figure return protection is important. Though I can't say that I have run any sort of scientific test, it seems to me that when operating my GW, if I run the stat up around 195 (185-205 °F operating range) It burns cleaner AND uses the same OR LESS wood.