Modulating Mixing Valve vs Injection

Mark J Strawcutter

> My understanding is <BR>
> that injection was started to fix the problems of <BR>
> jobs in the Northwest and Canada where a non O2 <BR>
> barrier tubing was used and this was the birth of <BR>
> Tekmar. <BR>
<BR>
How would injection fix the O2 problem? I'm not disagreeing with you, just trying to understand.

Mark

Chris Maderia

Modulating Mixing Valve vs Injection

Okay, men of radiant, which is better and why? I have been pondering in my head what advantage injection has over using a 3-Way Modulating Mixing Valve since this practive has been used for years, while injection is a fairly new practice. Seems to me that an installation using injection is more $$$ and for the life of me I can't figure out the advantage. Now I'm talking about whole house installations where you have multiple temps not a single temp.

My feeling is that injection is more expensive, has more room for error (ie, piping/wiring). But the question still stands. What's the benefit to the installer/customer as far as system efficiency/control goes?

My understanding is that injection was started to fix the problems of jobs in the Northwest and Canada where a non O2 barrier tubing was used and this was the birth of Tekmar.

Unknown

One of my favorites

The reason that caught MY eye, is the small size of the injection piping. If your primary loop is in the same room as the injected zone, it isn't a big deal. If your injection zones are far away from the primary loop, very, very small pipes can carry the load between the two loops and still heat a large space. I'm refering to pipes smaller than 3/4", even as small as 3/8", since the Delta T is great and the injection flow is small.

A large radiator loop on an upper floor can be served by a pair of small PEX tubes, snaked up through the walls, without much cosmetic damage. An attic air handler can be treated the same way. That leaves the larger circulators and piping in the equipment rooms with only small tubing connecting them, between floors and between mechanical rooms.

Noel

Bill Wright_2

Injection mixing is best suited for ...

High mass, low temp systems.

High Mass -- Injection mixing provides positive boiler protection from low return temps (for boilers that require protection). It also provides protection during "cold slab start up" each year.

Low temp -- the higher the required supply temp, the higher the required injection flow rate, the bigger the diameter of the "cross over risers". When your required temp is much over 150 deg you might as well use a mixing valve based on the flow rates (IMHO).

There are some who will argue over the longevity of a pump vs a thermostatic valve ... but everything has a given lifespan & I don't want to get into that arguement! :-)

By the way -- injection mixing isn't all that "new" -- B&G shows it in their manuals from the 1960's. I think Siegenthaler had a P&M column a few months back pointing this out. It does have some history ... so I wouldn't be afraid of using it -- but there are some applications where it IS over-kill (again, IMHO).

Boilerpro

My thoughts

Well relatively new to the field, my understanding is that one of the historic problems with mixing valves had was that they would get stuck. In addition I dont't think they can react very quickly (particularly the thermostatic types sold by most Rad floor companies). The getting stuck part can be solved by controls that exercise the valves. I also consider the fact that the most common part that will need to be replced on an injection system (not including VFD types) probably is the pump... and virtually any contractor will have a pump that will work in teh back of thier truck (UP42, 007, NRF-22). So far they have been all I have used, except in residential when I am looking for boiler protection only, then I use ESBE Thermixs on budget jobs.

Boilerpro

Chris Maderia

I'm still

really stumped here. What's the advantage of injection over modulating 3-way mixing (Not thermostatic). I've attached at piping schematic that I have been using for years with 3-way modualtion. The reason for this post is that everyone preaches injection but nobody seems to have an anwser to why it's the cat's rear-end. I feel that it has no system efficiency adavantage. If I need 120 degree water and I can get it with both what's the advantage.

With the system below I get total out-door reset with each zone with the benefit of only using 1 single simple reset control.

George Peteya

Relative Cost

Partswise, injection should be less expensive. Compare the cost of: tekmar 356, Taco 007, a flow check, and a globe valve, with: tekmar 360, 1 1/4" ESBE valve, and actuator. Only your heating contractor can compare labor costs, but at list price for parts, you're probably $500 for injection and $1000 for the mixing valve system.

RadSteve

Injection Mixing

The only difficulty I see with your design is that there is no condensing protection for your boiler. The injection method with a Tekmar 356 or Taco PC705 provides protection with a boiler return sensor.

Steve Ebels

Chris

I still like a motorized mixing valve. I feel it's more positive as far as temp regulation. Less ghost flow problems (and I've seen some that were a real pain to sort out with injection.) I've never had a mixing valve stick. I've never had one burn out either. (We are careful of water quality and use a strainer on every installation) We use ESBE or Viessmann depending on the job. 3 way or 4 way depending on the boiler and the application.

Chris Maderia

By-Pass

I should have been more specific, A By-Pass would be necessary with any boiler where you would worry about low return temps. I use this piping diagram with a Viessmann Boiler. I add a By-Pass when using any other boiler. The Modulating 3-Way in let's say with an American Boiler would be a Wirsbo Pro-Mix 101 with outdoor reset and Boiler Protection for about $450.00 or better yest Eries control whioch is the exact same control for about $100.00 less.

David Van Wickler_3

old article

Recently I was asked to design a large residential heating system. When it came to controls the owner had conducted an investigation that I have never seen before. He had accrued a inch of information on mixing valves and injection pumping controls, theory and applications. Ron was thoroughly confused as to which method was “better” for his application. I started thinking this confusion may be widespread. As I answered each of his 2,000 questions it was evident I wasn’t really sure which was “better” myself!

Mixing valves have been in use before I was born (1970). Many of these valves are still in operation and have cycled millions of times. That simple fact says they are very reliable. Reliability is important since failure typically means the owner pays again. This was my opening case for mixing valves. Reliability, quantities in use and contractor familiarity were strong contenders and contributed to my lean towards mixing valves in residential systems.

Injection controls are offered by all major manufactures. This control, which accurately regulates the speed of a common wet rotor circulator, opened the door to a new way of radiant panel water temperature control. And, as we all know, radiant heating typically requires some form of control to modulate the heat output of the radiant panel. In my opinion the greatest strength in injection control is the flexibility or control range that the control+pump offers. When properly set-up this type of system can handle nearly every type of heating challenge. With a few simple modifications the injection control is simply the best solution to water temperature modulation.

Mixing valve people may get upset but the fact of the matter is mixing valves require more effort in selection than most folks want to get involved with. Valve authority, CV ratings, etc. are conditions that must be analyzed in an effort to choose the correct size mixing valve. “I’ve been line sizing my valves for 20 years and have never had a problem”. Yup, I agree and that’s the same person that sticks a 4-section boiler in a 2400 ft² house! I’ll agree that line sizing works, just like the 4-section boiler will provide sufficient heat. But that’s seriously limiting the ability of the device to operate correctly. Line sizing a mixing valve is just as hit-or-miss as saying, “Install one line size smaller mixing valve”. I know because I’ve used the above as a rule of thumb for several years. I theorized that it’s better than line sizing. Go figure. Additionally, and this is my favorite point, mixing valves and mixing valve motors require mechanical help. Gearing and multiple motors are required to change direction in most motorized mixing valves. Have you ever met Murphy’s Law? Remember reliability? An injection control+pump has but one moving part and one electronic component. Also, mixing valves can be piped in several directions and the final valve rotation may have to be reversed. Next to over sizing is incorrect rotation of the mixing valve. It’s not much fun in the winter wondering why the supply temperature gets colder as the outdoor temperature gets colder.

The greatest disadvantage of over sizing a mixing valve, or boiler or injection, is the inability to accurately control the system supply temperature it’s connected to. If the control acts in an on/off or a short cycling condition, you should have offered the customer a programmable light switch! On/off/on/off is an antiquated means of control and is one of the main reasons fancy controls were introduced to the industry.

Mixing valves are great devices and when sized correctly and when dialed in properly will operate for years. They are familiar to all radiant contractors. But they are typically line sized or minimally scrutinized for proper selection. This leads to a heating system that hunts and operates in a restricted range of valve stem motion (operating between “0” and “1” with a maximum scale of “10”). When you oversize a mixing valve in a radiant heating system the port that allows hot boiler into the valve, to mix with the return water, is so big that too much hot water enters the valve, even when the valve is nearly closed. This is due to the fact that the available area offers too little resistance and the opening is too large to limit the hot water flowing into the valve. The valve must have some resistance to give the valve the ability to control the flow from the boiler and the return flow from the system. Remember in a low temperature radiant system it doesn’t take too much 180F water to raise 110F to 120F. A line sized or oversized valve will hunt back and forth in an attempt to stabilize the mixed outlet temperature. Every time the valve opens the boiler port hot water rushes in unimpeded and spikes the outlet temperature. The sensor in the valve or in the mixed piping senses the quick rise in temperature and the valve close. On/off/on/off/on/off all winter long. The valve has no control.

The same holds true with injection pumping at low load conditions (spring/fall) or in small systems, the smallest circulator is too large. This problem stems from two issues. One is the size of the system or load and the other is the pressure drop through the injection piping. At low flow rates there is very little resistance. I’ve pipe injection systems with 3/8” copper in an effort to increase the resistance in the piping. Even this size pipe is too large at very low flow rates that are prevalent in small systems. The injection pump needs a pressure regulator on the discharge of the pump to provide a resistance against the pump. Put another way, the pump needs to fight against something (will a pressure by-pass valve provide the necessary resistance at low flow rates and provide resistance for the pump?). Just like the mixing valve the injection pump loses authority – in fact the primary pump and piping can produce enough pressure drop across the closely spaced tee’s that flow is produced across the injection piping when the pump is off! At low loads or low heat loss the secondary circuit (the radiant zone) can overheat. At this point a simple thermostatic mixing valve would produce the same overheat condition and cost 10X less. Thermal trapping does not prevent ÄP induced flow. Check valves prevent flow. Every injection pump should have a flow check installed. Preferably a check valve integrated in to the pump. Why? Because the manufacture has properly chosen the check valve and it will be quiet. Low flow rates can cause check valves to bounce and clatter. I transgress.

What makes injection better than mixing valves in the majority of heating systems? A non-related device. The flow meter. I started specifying flow meters with all my injections system in residential design. The flow meter also provides some pressure drop and increases resistance for the pump to overcome. Also, please install a fine mesh strainer before the meter. This prevents stuff from binding the flow meters parts. Also, pipe the injection circuit in copper. Some flow meters are high temperature plastic and steel piping can place stress on the meter causing it to stick (ask me how I know that). Copper allows a slip fit and adjustments can be made that will minimize pressure on the meter. Flow meters with internal plungers or dials may discolor over time since the operating fluid will tend to suspend rust and other yucky stuff. The meter, once set, should not have to be readjusted as long as the identical pump is used when replaced. A simple 6-dollar ball valve is all that is needed to adjust the flow meter. To dial in the flow meter simple set the control in manual or set point temperature mode. Ensure all zones are off. This way the secondary sensor won’t measure any temperature since the zone pumps are off. With the injection pump running 100% close the ball valve until the flow meter is set to the correct design flow rate. You have now adjusted the injection pump to meet all flow conditions. And you did this in August when it’s 110F outside!!!!

Here are several flow meters. I tried all three and the price range is from $40-150. The question I ask is, for 60 bucks (meter and strainer) why wouldn’t you install one? The real question is; how else would you adjust the injection pump to produce the correct design flow rate?

Out door reset or accurate set-point control systems rely on properly sized equipment. For any room or system larger than a kitchen the injection pump+control offers more than any other water temperature control. Injection is more flexible, has fewer moving parts, less electrical components, operates with less noise and typically cost less. Sounds like a winning combination to me.