Reliability of Danfoss Thermic Valve

[BoiledOver]

Have ya monitored your in and out temps while using an ESBE thermic valve?

Last year I ran it the whole time without temp sensors on the in and out. After assembling a new control box and installing more sensors, a concern became evident. The recommended thermostat for return side is rated at 140 F, so that is what was used. What I saw early this season was very low return temps, 113, 119, 126, with temperatures out, 155, 170, 180 and such. Cripes there must be some debris keeping the valve open. So after a remove clean and replace things should be good. Well there was no debris visible to these bespectacled eyes, but still the assumption is that it will purr at 140 F. Wrong, same temps.

So maybe it is just a bad element. Got a replacement 140 F element all screwed in and guess what, same as before. Decided to order a 148 F and a 158 F. Installed the 148 and now things are good. Once the boiler reaches 150, the return temp runs about 145 on average until nearing the end when the bottom of storage is now hot also and the valve is wide open. Sometimes early on, it will drop to around 133 but it is a momentary thing.

This Danfoss valve is located on the return side upstream from the circulator. The return sensor is located between the circulator and the boiler. The boiler out sensor is after the other boiler loop tee. See picture below.

So, I feel good about how it is now working and wondering if anyone else has used one of these valves without sensors to monitor how well it is mixing.

 

[jebatty]

A balancing valve on your supply to storage will work to force more boiler output through the Danfoss and maintain the 140F desired return temperature. The low return temps result in part from the very cold water being returned from your storage. What is your bottom of tank/return temperature? As storage warms and return from storage rises, the balancing valve can be opened to allow more hot water to flow directly to storage and maintain the desired 140F return temperature. Thermic valves are not perfect.

Another way to understand what you are seeing is related to the relatively low output of the EKO 25 and the flow rate of your circulator. With temps at 113/155, delta-T = 42 and assuming full rated output at 85,000 btuh, flow rate of only 4 gpm will move your entire output; thus the very low return temperature.

 

[BoiledOver]

Well stated Jebatty, I do understood what you are saying.

In my mind, the flow rate and differing temps can be whatever they may be. My assumption is the "automatic" valve should do its part in controlling the mix. Actually the Danfoss does a very good job provided the element is manufactured to the correct temperature. Unfortunately for one entire heating season the boiler was not getting the protection that I assumed it was. As it stands now, the 149 F element acts as I expected the 140 F to act and this is no longer an issue for my system.

Lesson learned, monitor the in and out temps. Without continuous monitoring it would be iffy to catch a failing component of the thermic valve.

 

[jebatty]

I believe I made an error. The balancing valve should be after the T and before the Danfoss.

 

[BoiledOver]

Maybe you were correct in your original statement. The valve after the tee towards storage when slightly closed would restrict flow to storage, yes? My understanding is the Danfoss does the throttling in place of a human manually adjusting a valve handle.

In any event, the Danfoss with the higher element is working well at protecting this boiler from undesirable return temps.

 

[hartkem]

Boiledover,
Where did you purchase the new elements and what did they cost?

 

[jebatty]

I think the "normal" installation would be for the balancing valve after the T and before the Danfoss. Water flows according to the path of least resistance. I would think that a "normal" installation has higher pump head through the T and through the system, and lower pump head after the T and before the Danfoss. Therefore, more water may recirculate through the Danfoss to the boiler than is needed for return water protection, and thus the need for the balancing valve in the "normal" situation.

Regardless, good to find a valve that works appropriately. You still may want that balancing valve. I find it to be very useful in my system, especially with very cool return water from storage (less than 120F).

 

[DaveBP]

I have also noticed a difference between the thermostat rating and the actual mixed return temp to the boiler.

I concluded that it is the difference between how they rate the element and what it actually does when installed in a system.

The manual that came with my Termovar Loading Unit says that the valve starts to open 27 degreesF before it is fully open. So somewhere in between those two limits is where it will mix to during much of the firing cycle.

 

[BoiledOver]

Jebatty, The truth is, I have no understanding of the workings of a balancing valve. The name itself has an implied definition, yes?

There are two different "after the tee and before the Danfoss" locations and we may have assumed opposites. I now see where your theory concerning the balancing valve makes sense.

In my mind, if the thermic valve (or any other type of mixing valve) is working as designed, there would be no need for a balancing valve. Is that a flawed assumption?

 

[maple1]

Jebatty, The truth is, I have no understanding of the workings of a balancing valve. The name itself has an implied definition, yes?

There are two different "after the tee and before the Danfoss" locations and we may have assumed opposites. I now see where your theory concerning the balancing valve makes sense.

In my mind, if the thermic valve (or any other type of mixing valve) is working as designed, there would be no need for a balancing valve. Is that a flawed assumption?

I don't think it's flawed. I have said the same thing more than once around here. It's been a while though. Makes me feel a bit better hearing someone else say it too.

 

[BoilerMan]

I don't understand the need for a throteling valve either. If anyone else is familiar with a water cooled VW thermostat, I'm not sure why a Danfoss valve is not made the same. In the fully closed position the coolant bypass is fully open, likewise when the radiator passage is fully opens, the bypass is fully blocked.
https://www.google.com/search?q=198...3DVW%26Part%252520Manufacturer%3DFebi;222;225
TS

 

[mr.fixit]

The thermostat in my Danfoss isn't a blocking type, when open it will still allow some flow from the bypass.

I believe there are couple different types of danfoss around,some look more like the smaller mixing valves and some (like mine) have the big cast housing with the bolted cover and automotive like thermostat element.

 

[BoilerMan]

If I ever design a return protection valve it will have a simple automotive thermostat of the blocking type. As little restriction in the overall piping w/o the need for a throttling valve.

TS

 

[Bob Rohr]

There are 3 way thermostatic valves designed specifically for boiler protection. High Cv and 100% shutoff can be designed into the valve.

In my case I started with a 140F sensor, but he boiler when to high limit before the bypass closed 100%. This is due to the 18 degree differential added to 140 = 158 return temperature required to close bypass.

So I changed to a 120F sensor add 18 = 138F at return, bypass closed 100%.

Not all these 3 way valves operate or regulate the same, and a manual valve is kinda forcing the valve to do something it wasn't exactly designed to do. I think.

 

[ihookem]

Sounds like it was sticking . Mine seems to get stuck closed and lets out no water even when the boiler temp is 170, the water temp in the house is cold. A few times I had to bang it a little bit and then it opens up. Has not happened in a long time though.

 

[jebatty]

In perhaps a somewhat more generalized view, my thought is that the Danfoss (or the Termovar, which I have) was not really intended to handle the wide temperature range that is possible with very low temp radiant to very high temp water/air hx or baseboard combined with high volume storage. My low temp in-floor system with 1000 gallon storage can operate down to 100F and also does fine at 190F (mixed down to 100F). The Tarm should see minimum 140F return water but really purrs with 160F return water.

If I keep storage at about 140F minimum, the balancing valve is a "set it and forget it" thing: adjust (mostly closed) so that at 140F from storage results in 160F return water to the Tarm, and no other adjustment is needed, even as storage temp rises to 190F. But at storage below about 140F and then all the way down to 100F (or as low as 60F at the start of the heating season), the balancing valve needs to be open much more to allow a lot more of boiler output returned to the boiler with limited mixing of cold to cool water from storage, and then as storage temp rises the balancing valve can be throttled back. And since I commonly run my storage down to 110-120F before re-firing the boiler, I need to adjust the balancing valve mid-course as temp from storage rises.

Since it takes several wood loads to bring storage up from 110F to well above 160F, I have no issue with adjusting the balancing valve mid course. My balancing valve is a 1-1/4" gate valve. With cold storage return water, the setting is 2-1/2 opening turns of the handle from fully closed. With storage return water at about 140F or above, the setting is one full opening turn of the handle from fully closed. In other words, the gate valve is barely open.

The Termovar is of European origin, and maybe when it was developed European systems operated within a more narrow temperature range which only required a "set it and forget it" for the balancing valve. Not perfect in my application, but the mid-course correction required in my system is of minimal inconvenience. Having to re-load several times is far more "inconvenient" than making a slight adjustment of the balancing valve.

I also am experienced with at Wood Gun E500 that has a motorized return water protection valve. It does what I do manually, but since it is motorized with a temp sensor, it makes more corrections as storage temperature changes to maintain 160F return water. I don't know enough about an auto thermostat to understand whether it would work as needed to maintain boiler return water protection. If so, then it would seem to be a fairly minor plumbing change to incorporate one into a wood boiler system. Does anyone want to try it?

 

[woodsmaster]

I've had no problem with my termover 140 degree valve in four years now. It does return the water at 150 instead of 140 but that's not a problem to me. I'm also pulling 110 degree water from storage a lot of the time with 1 1/2" pipe. I have a y strainer just before the valve.

 

[maple1]

I am sticking with my opinion that if a throttling valve is needed with a thermic valve, along with constant fiddling with it - then something isn't designed or manufactured right. The fiddling with the throttling valve is doing what the thermic valve is supposed to do.

My loading unit is essentially the same thing - except that the pump is built into the thermostatic body. No throttling valve or fiddling there - when the pump starts, the return water being sent to the boiler goes to 140 no matter how cold my storage is, until it rises as cold storage return water gets above that point. A separate pump & thermic valve should work the same way.

Defective engineering.

 

[Fred61]

I think the simplicity of the Danfoss is being overlooked here. Although I'm not familiar with the Termovar nor the latest Danfoss which I understand is supposed to be self restricting, I became quite familiar with the older model Danfoss which came with my boiler because of some problems I had early on.

Mine is simplified because my loop is short and has little resistance (head) since I only heat to storage which is a very short run. The bypass of course must have some flow at least because that's the vehicle that sends the boiler water through an over the sensor bulb on the thermostatic valve and will cause the valve to actuate when water from the boiler reaches the temperature value of the bulb. If there was no flow through the bypass the valve would never open. So until the boiler water reaches the thermostat value, any amount of flow through the bypass is OK. However, when the valve opens and from there on up to your upper setting, flow becomes an issue. Chances are your heating loop or loop to storage is going to have more resistance than your bypass loop and that's where your resistance valve ie. throttling valve comes into pay. If you don't at least match the resistance of the bypass with the resistance of your heating loop, more flow will pass through the bypass and will not take the heat away from the boiler resulting in lower efficiency and possibly more idling or overheating of the boiler.