Four-Way Mixing Valve

[Eric Johnson]

This is the first in a series of threads I'm going to be starting trying to learn more about wood gasification boilers, since I'm planning to buy and install one (probably either a Tarm or an Eko) over the summer. Craig is always very helpful when I PM him with questions, but instead of bugging him exclusively, I figure it makes more sense to just put these questions out there and see what the collective intelligence comes up with.

From what I've been able to learn so far, it's a good idea to have some type of water storage with a gasification system, both for the sake of efficiency and boiler maintenance. One option is to put a 500-800 gallon tank in the basement to store heat. An alternative would be to add a four-way mixing valve to my hydronic heating system, and essentially use the water in the system to store the heat, while it's heating the house. I think I have an ideal setup for that, but I'm not exactly clear on how a valve like that would work.

I'm guessing from the name that a mixing valve like this would mix cooler return water with hot supply water, thus putting somewhat cooler water into the hydronic distribution system more evenly, instead of hot bursts when the zones call for heat. But I'm not at all clear on how that would work when it comes to pumps, aquastats, thermostats, etc.

I have a big, old house with 15 cast iron radiators and three pump-driven zones. The main zone contains 11 of those 15 rads (the original farmhouse). The whole system must contain 300 or 400 gallons of water when you consider what the old gas-fired boiler holds in addition to the radiators. There are a couple of rooms where I'd like to put in even bigger radiators, which would add even more capacity. The system is currently heated with a non-gasifying wood boiler that transfers heat into the gas boiler vessel through a flat plate heat exchanger.

So, can somebody give me a simple explanation of how a four-way mixing valve would (should) work in this situation?

ps - Note to Marty S: Yes, you made me think.

 

[elkimmeg]

eric are we talking about one main manifold into 4 separte zones controler by zone valves? using one circulator pump or 4 zones and 4 cir pumps?
It can be done either way the pump way cost more than zone valves. then there is the electrical needs the zone valves are controled by a voltage step down transformer there are two common transformers one that does 3 zones or a five zone one then th two 3 zine transformers can be piggybacked to control more than e zones up to 6 zones Many times when adding an additional 4 zone the transformer is often overlooked and causes voltage drop to the zone valved burning them out.

the eazist one to wire would be the single 5 zone transformer I seen too many screwups in the piggyback situations.

Explain more of what youare doing I would think you need to even out the zone demand and capacities /runs and not have one zone overloaded and one with fewer radiators

 

[Eric Johnson]

I'm not sure what it is, elk. Craig (and others) have said that you can put in a four-way mixing valve to get around having large-volume water storage with a gasifier. I'm trying to find out what that is and how it works--specifically, how it would work in my system.

Currently, not counting the greenhouse, I have three zones controlled by three thermostats and three circulators. When I'm running the wood, which is to say all winter long, I shut off the gas burner and circulate wood-heated water through the gas boiler to keep it hot. The zone circ pump circuit runs through an aquastat in the gas boiler that breaks the circuit on cold days when the temp gets below the setpoint (140-120) so that the wood can catch up. It's basically a big momentum arrangement. I'm guessing that would be even more the case with the mixing valve, though that's just an uninformed guess.

But to answer your question, I've got one manifold for the big zone and another one for the other two (three if you count the greehouse, which I don't currently use in the winter). No zone valves, though I'm considering putting a couple on the big zone. Trouble is, there's a lot more iron than copper in that zone, since it's the original part of the house, so putting in zone valves is more of a challenge.

 

[Eric Johnson]

OK, pretty simple. Here's what they look like. That's about $400 for a 2-inch model with manual control. You can hook them up with motor drives actuated by a thermostat that measures outside ambient temps. What it does is mixes supply and return water, which is constantly circulating, to achieve a set temp throughout the entire system. This reduces fuel consumption and thermal shock to the boiler, plus it provides even heat throughout the house. To run it manually, you just monkey around with the settings and figure out, over time, where to set it for which outdoor temps. I've done that before & it's not as hard as you might think.

The trick with gasifiers, as I interpret what Craig told me, is to keep them running constantly within a fairly consistent temp range. So with a manually-adjusted mixing valve, you have to keep track of the outdoor temps and make sure you're giving the boiler enough fuel to maintain temp. Meanwhile, you need to keep track of the mixing valve settings so they correspond to the weather as well. It sounds like a lot of work, but I like doing that sort of thing. You just incorporate it into your re-fueling routine. One of the really nice things about the Internet is that you can get pretty good weather forecasts any time you want.

 

[Eric Johnson]

bump

I still have some questions. Anybody?

 

[webbie]

Here is what I know about mixing valves - they make ANY hot water system much better for a number of reasons. 3-way or 4-way are used in most in-floor systems, but in that case the main function is often to lower the temperature of the water since most rubber tubing doesn't want water above 140.

OK, so here is how they work....picture it as one zone, since you would need one valve per zone - but in the real world, a 4-way is usually only used on the largest zone -a zone that would usually be the zone that needs heat most often (living as opposed to bedroom).

Now picture it - or draw it on a piece of paper as a figure 8. The 4-way valve is located at the middle where the lines intersect. The bottom loop is the boiler , the upper loop is the house radiation and contains a circulator.
Notes:
1. The circulators runs 100% of the time - but see Idle below
2. The valve is set at a "idle" setting, which for instance might circulate 180 degree water in the bottom loop (this loop is located next to the boiler and contains no radiation) and 110 degree water in the upper loop. This idle setting can easily be changed for the colder weather when you might want a higher idle.
3. On a call for heat from the thermostat, the valve starts opening slowly and now the radiation loop goes to 110, 115, 120, 125 and slowly up until the thermostat is almost satisfied (anticipator) and then the valve slowly closes back to idle.

In many scenarios the valve never opens fully nor closes fully.

The result? Lot of benefits.
1. The boiler stays at 180 and does not experience the shock of very cold water coming back into it.
2. The radiators do not creak
3. The house feels more comfortable
4. All water in the system is kept at least at the idle temperature, which does add the water in the house to the storage - at least to some level
5. Less prone to overheating because of #4.

These valves are used in the majority of European hydronic systems and they should also be used here - people would be much happier. A good way to think about it is this - what if the cruise control on your car was the same as a regular boiler - it would floor the gas pedal when speed was needed and then provide no fuel when it was not. A better system is one that modulates the gas or heat - that is a mixing valve.

 

[webbie]

OH, a manual one does you no good - you need to get one with an automatic head that can be attached. These usually operate on 24 volts from a transformer which is controlled by your thermostat relay.

You need one of the brass valves and one of the motor from below:
http://www.acaso.se/english/produkter.htm

 

[Eric Johnson]

Thanks Craig. Yes, I concluded this morning (after sketching the thing out like you suggested) that a motor tied to a room stat would be the way to go. I couldn't figure out how the thing would work (i.e., how would it know how much to open the valve?) but I think you answered that. Plus, I don't have know to know exactly how it works--just so it does.

My biggest zone, as I think I mentioned, contains 11 of the 15 cast iron radiators in the house. So that's obviously the one. I might even be able to get away with gravity feed since it's all fairly large diameter piping and in a pretty much vertical orientation in a two-story house. Somebody told me once that if you open the flow control valve on the zone, it will convect. But since I have a pump on that zone already, I can try both approaches and go with what works best. Would the pump ever shut off?

But just to see if I get this straight: To keep the house at a consant 72 degrees on any given day, all the radiators would contain a constant flow of, say, 120-degree water, instead of intermittently cycling between, say, 80 degrees and 160 degrees. And the mixing valve, room stat and motor control would do all that, as long as you maintained enough hot water in the supply line?

I am concerned about response time. Wouldn't it take a long time to heat the house up with a system like this? Would it hold the heat for longer?

And finally, is it a viable substitute for water storage with a wood gasification boiler? If so, it sounds like a great investment.

 

[webbie]

1. It is not designed as a subsitute for water storage, but it will work that way to some extent in your case because of the large water and iron storage of the radiators.
2. Response time is quick because the radiators are already lukewarm (idle is adjustable for mid-winter, etc.) - so they don't have to go from 0-60.
3. The pump on a mixing zone valve runs full time, but it can be a very small grunfos or taco unit and uses very little current.

In terms of operation, it would more accurate to say that the water will vary between 110 degree (idle) and 180 (full bore) depending on the heat load of the house - the valve opens and closes slowly on purpose - so in some cases it is always opening or closing...based on the call of the zone (thermostat).

You don't really have to engineer anything except a little re-piping right at the boiler. The thermostat calls on your boiler control which then...instead of turning a circ on, will turn on the mixing valve head.

 

[Eric Johnson]

Thanks again, Craig. I think it's really going to work well.

I had Carpniels over for dinner last week and he looked everything over and had some great suggestions. I think I've got the hook in him far enough that he'll help me pull the old boiler out and put the EKO in this summer. I may have to lay a load of wood or two on him before it's all said and done. It helps that he's an engineer (with a strong back and a good attitude and an appetite to match). And a great guy.

 

[Eric Johnson]

Mixing valves can be pretty expensive, not to mention the cost of the controller and other necessary hardware.

However, after shopping around on the Internet over the weekend, I did find a Honeywell 1.25-inch four-way mixing valve for around $60, plus another $120 for the motor and about $75 for a compatible room stat. I'm not sure why this one is so much cheaper that others I've seen. It's a little smaller and it's made of cast iron. But it looks like the right gear.

http://customer.honeywell.com/honeywell/ProductInfo.aspx/V5442N1031