Condensing boilers/ VSI or Mixing valves?

heatboy

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heatboy

Just so you guys.......

don't think I have a closed mind, can we discuss this? hydronicsmike's post in the other thread got me to thinking which is the best way to mix when using a condensing boiler with full boiler reset. VSI will certainly work with any type of equipment. It just seems, to this limited wethead, that motorized three ways would be a better option.

Observations:

Since any mixing device needs a elevated supply temperature of 20° to assure mixing, both methods require warmer than needed boiler temperatures. Not much we can do about that.

When utilizing boiler reset, the mixing valve will be for the most part be almost completely open. The mixing valve uses very little electric compared to a pump. Only one pump down stream (on the mixed side) and it's associated power consumption are needed. Since a primary pump isn't needed the return temperature will be as low as possible.

When utilizing boiler reset, the injection pump, if properly sized will be running almost full speed constantly using substantial electric over a season. Since VSI is just a bridge, two more pumps are needed to complete circulation. The system (mixed) pump and a primary (higher) temperature pump with their inherentl higher electrical loads. Since this primary pump must run whenever there is a heat requirement, it will also increase return temperatures, which is not optimal for condensing.

Is this correct? If I am wrong, which would be no surprise to me, I will have to examine the way I offer my systems.

Thanks for the help!

hb

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bigugh_4

an old man here

would say Simpler is better~~~always. Useing a thremonally activated temperture control mixing valve (many excellent brands) properly installed will last longer and cost less to operate (no power). I hope this helps

Unknown

HB,

I also have been re thinking the way I I deal with condensing heat sources. I just started installing Monitor MZ wall hung boilers. I simply can adjust the desired main heating loop temp. output by twisting the dial on the front. Floating action 3 way valve keeps up with the pace. I really like these machines. Fit & finish is right up their with the Vitoden$.

The motorized 3 way valve makes the most sense to me right now. Simply because it's easier to understand in concept and effectively gives the desired temp without much hunting. It floats alongside of the heating curve in parallel with anticipated output. Splitting hairs makes no business sense to me. VSI is awesome however, IMHO not all that it's cracked up to be. Sorry Siggy;-)

1 vote 3 way

*To catch up with me real time, try AIM. User name: Radiantfloors*To catch up with me real time, try AIM. User name: Radiantfloors

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Unknown

A

oops

John McArthur

3-WAY valves

What brand of 3-way valve do you use? Do you use a second pump for indirect DHW, and have some type of control to override the low temp of the condensing boiler? Or do you use a seperate water heater? I install a lot of p/s systems using atmospheric boilers systems, but I am interested in installing more high efficiecy boiler systems. I have a 16-plex with radiant floors that I'm installing Triangle Tube Delta combo units and they are working great. Any opinions on the Delta's?

Mark Hunt

Agreed


motorized 3-way valves with condensing boilers.

Mark H

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Ted_5

3-way has my

vote. If I use an old ironside with P/S, I use a 2-way valve in-jection nonelectric or motorized with an outdoor reset control or motorized 4-way These all use on less pump then VSI.

Ted

Ted_5

Hi John, and HB

here is a picture of a system with 3 temps. Boiler temp runs the upper manifold with a mix of heat, mostly baseboard
1 flat panal rad [radson] and some staple under the bathrooms. The 3-way is not motorized it runs proportionally
with the boiler reset. That not the preferd way, but it helped on the budget and the basement was not finished of yet. The motor could be added later when they finish off the basement. The other temp is the DHW. All done off of the control that is standard on the Vitodens! Only two pumps in the system. The boiler pump runs the upper manifold
the DHW, and the P/S to the 3-way. I took the 3-way off the return to get the coldest water back to the boiler. 1 pump to run the radiant. What do you think?

hydronicsmike

3-Way and VSI

I agree with all the points made about the 3-Way Mixing Valve. It is always a matter of preference. I can see why you favour 3-Way Valves instead of VSI when it comes to power consumption and ease of Installation.

I just wanted to point out that when someone tells me that you can't use VSI on Condensing Boilers that this is not neccessarily what I believe because of the obvious points stated in the other post.

I would never say one should use Injection over a Mixing Valve. It is always a personal opinion and what one feels most comfortable with. I know a number of people who'll only do VSI, but on the other hand I know people who won't touch it. Both will get the job done. One may react quicker than the other, but may draw more power. Fair enough, I guess, although I am not quite sure if it draws so much more power so that we would start losing a considerably amount of money here. What would it be, 1-2$/month? If that. Those Pumps available, let it be Taco, Grundfos, B&G, Armstrong or others, draw so little power. I'd be surprised if you could notice it on a utility bill at the end of the month. Again, the power consumption statement sounds European to me

HB: You mentioned that you need only one pump when using 3-Way Mixing Valves. I know what you mean, but with most North American built boilers, don't you need the proper flow across the Boilers Heatexchanger to get the proper deltaT across it? With a single pump in the system, I can't see how this can be assured. Even when I use Mixing Valves, do I install a pump on the boiler and on the low temp side, using the Primary/Secondary Piping arrangement do isolate the two. Then the boiler pump always ensures my proper flow across the boilers heat exchanger and I got the flow I need to the zones.

If you install only one pump, then how much flow do you have going through the boiler once the Mixing Valve closes. The more it closes, the less flow across the boilers heat exchanger.

Mind you, some of those boilers nowadays are so well designed, not all of them care about their flow. Either because they don't need it, or, because the boiler manufacturers take care of that themselves and install pumps right inside.

Many of you may not know. Where I learned the Trade (Germany), VSI Injection was not used or even talked about over there. Its all Valves, let it be 2, 3 or 4-Way. Naturally, myself being a German and all, when I first came over, I jusy shook my head when I saw a VSI install and tore it right out. "This VSI can't work! These guys are nuts over here. If VSI Injection truly was as good as I hear people say, we would have done it in Germany years ago. In fact, if it would, we would have invented it!" This is what I said and thought for the first two years of being here. I hated VSI, cause I wasn't familiar with it. One very fine gentleman, Barry Cunningham of Triangle Supply in Red Deer, AB, a wholesaler whom I worked for then, took me aside and said "Listen, stubborn German Boy! Let me tell you about VSI". He did. He spent nearly a month trying to convince me that VSI is still good, although it is not done in Germany. On a weekend, I finally gave in and built my very first and very own Injection Panel. It nearly blew me away when I realized that I had been wrong! VSI does work.

For the first time in my life, I had to realize that only because something isn't done in Germany, it may still be alright !??! Today, I know the features and benefits of VSI and I will swear by it until I learn better.

Sorry for making this post so long....it's the German and passion for this industry I got in me.

Have a great weekend everyone!

Mike

hydronicsmike

By the way HB...

...I love the pictures you post from the jobs you do. One can tell that you take pride in your craftsmanship.

heatboy

Well, I for one.......

didn't know anything about your background, Mike. Very inpressive. I'm just a knuclehead with no formal training in anything except mistakes ;-) And there have been many.

As I said, I have no problem with VSI. I have done it before and will quite possibly do it again. Depends on the equipment I'm working with. Admittedly, a majority of the stuff I do is Viessmann so mixing valves are the only, and rightfully so, mixing option. That's not to say I wouldn't put a Wirsbo 311P with on of their cast iron boilers. Just haven't yet. Flow rates inside the Vitola, Vitorond and Vitogas are not critical, hence the mixing valve selection being the best option for those as well as the Vitodens. The Vitodens, as you know, does have a boiler pump. I can run a mixing valve downstream of the LLH with only one pump, as opposed to having the system pump, VSI pump and creating a primary loop downstream of the LLH with a pump.

Thanks for the nice words about the work. For years after the project is finished the panels will be the signature.

hb

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Darin Cook_2

Pumping Methods

It is a interesting debate over what is a better method VSI vs Mixing valves. But quite frankly when you can reduce a customers heating bill by half just by choosing a condensing boiler it is not worth the argument quibling over the two. I will say this, if you choose the wrong pump when choosing valves over pumps you will have a very unhappy customer. I do not post very much, but the quality of mechanics who will argue over these facts are head and shoulders above the rest of the pack already. I have been to both HTP and Viessman traing and what is taught at both training centers is very sound and energy efficient. Keep up the good work all who bother to even think at these levels.

Steve Ebels

How many

How many of us here have used a Viessmann Divicon. (That's their proprietery mixing valve) I have to say on the
systems I've used them on, the installation time for the mixing valve portion of the work was 1/10th of the time of piping in a regular mixing or VSI setup.

If you have, what kind of results did you have with it? Which boiler did you use it on and have you ever had any trouble or undue maintenance with it?

heatboy

Splitting hairs

Yes, I concur, it probably is. Choosing the "best" control logic for any system, especially a condensing system with it's premiums is, I beleive, the critical component to whether you have done the best you know how for your client. To attain those precious extra points of efficiency with a condensing boiler, this is the stuff that must be considered. And besides, it's really cool and fun to discuss;-) I wish we were around a table with a few Guiness'!

hb



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kf_2

VSI vs 3-Way Mixing

I think that the question was, which method is better for condensing boilers?

VSI was designed to do to things. (1) Deliver the proper water temps to radiant or low temp systems. (2) Protect boilers by keeping the boiler loop and the boiler out of dewpoint. Unless the VSI loop is the boiler loop. This is rarely the case becasue the boiler is being used for other things. (DHW,etc)

On the radiant or low temp side both methods work fine. However, on the boiler side there is a BIG difference.

On a condensing boiler if the return water temps are not below the dewpoint (approx. 136 degrees F. for Nat. Gas) then there is no condensation on the fire side. This means that you have sold someone a higher priced condensing boiler that only sees about 85-87% efficiencies.

Also, do not overlook the added electrical expense of more pumps. Mike said earlier in this post, "what would it be 1$ to 2$ per month, if that" In reality the cost of a Taco 007 designed for constant circulation is about $7.20 a month at $0.12 a KW.

(120 volts x .7 amps = 84 Watts) (30 days x 24 hours = 720 x 84 Watts = 60,840 Watts or 60.48 KW) (60.48 KW x $.012 = $7.20)

A Taco 0011 which is commonly used in radiant & low mass boiler applications at 1.76 Amps would cost about $18.25 a month. OH BOY!! Thats $219.00 per year. In my house that would be almost 25% of my yearly fuel cost.

The Germans have to subtract this consumption from the boiler efficiency.



kf