Termovar problem

[dogwood]

Greg, when when the boiler is cold and the valve in your picture is in the closed position, is all return flow from the house loads to the boiler cut off? I think that is what you are saying. Or is it only flow from the line that provides the water from the boiler to mix with the return water, that is being cut off? Or is it flow from both lines?

I called BioHeat last week with a similar question. They answered that the Termovar cut off any return water from the house loads when the boiler was cold. I didn't understand the mechanics of how this might be accomplished until I saw your explanation and picture. I'll have to take a closer look at the Termovar schematic to see how the valve is situated. Thanks.

Mike

 

[Bad Wolf]

Picture the termovar with the boiler water coming in at 12 o'clock and the water from the house/storage unit coming in at 6 o'clock and the return line back to the boiler going out at 9 o'clock. When cold, valve is closing off the 6 o'clock side (house) completely, so it is 100% boiler water. As the valve heats up that pin pushes out and lifts the valve up off of the seat allowing some of the house water to mix. It actually takes about 20 seconds to move so the responce time is not real fast.
There is never any restriction of the 12 o'clock (boiler) side of things, thats why I'm saying that balancing valve is what I use to reduce the flow to give the house water a chance.

Right now my storage is down form over night so I'm seeing 170 form the boiler mixing with 134 from storage to yield 164 back to the boiler return.

When I turned up one of the thermostats, I still had 170 from the boiler but 141 return from the house with a result of 154 to the boiler return. So at 141 the valve must be farther open.

 

[webie]

Greg , Not sure how your storage tank is set up but mine I have anti siphon valves on it and these greatly reduce the pumps ability to circulate water increasing head pressure and reducing GPM. This is what has puzzeled me was my colder return water from storage was yielding higher mix water temps .

 

[jebatty]

Did a quick check on Termovar operation this afternoon that may be helpful. System return was 133F, boiler supply was 185F, and I set the limiting valve on the Termovar to provide return water at 160F. I have a flowmeter on my system that provides relative information, not exact gpm's due to the way I have it set up. With this configuation, flow was 4.5. I then turned the limiting valve wide open to the Termovar, flow dropped to 2.5 and return water temp rose to 169F.

I couldn't get a reading with the limiting valve fully closed in this situation, as the 133F system return water quickly closed down the Termovar. Perhaps in the next day or two I will run the system to bring the storage tank bottom above 160F, and then run the test again to see how much flow increases when the limiting valve is fully closed.

 

[webie]

Jebatty that is very interesting experiment , I would have thought the flow would have stayed the same and just diverted more return water as you closed the limiting valve . I would be courious at where the breaking point is as how much you can close the limiting valve before it starts to limit cold return flow and actually start to decrease the GPM There doesnt seem to be a direct relationship to the actual mixed return water temp ( or is there ?) , but at some point the termovar valve must start to say hey thats enough cold return water and start to slow the cold return flow and over all flow . Obviously you need some flow to open actuate the termovar but how much ?
I am thinking here to that maybe the best investment for anyone doing an install would be to install a return flowmeter as this is probably the most acurate way of actually setting the diverter valve .

 

[jebatty]

I am thinking here to that maybe the best investment for anyone doing an install would be to install a return flowmeter as this is probably the most acurate way of actually setting the diverter valve .

Although a flowmeter is useful (especially to calculate btu output and btu transfer), I don't think it is overly helpful in setting the diverter valve, which I am calling a limiting (or balancing) valve. I think the best thing to do is to have a thermometer on the boiler return line after the Termovar, and then set the limiting valve to achieve the target boiler return water temp, 160F for example. When system return water is "cold," the valve needs to be set to allow more boiler output to flow to the Termovar to balance the cold system return and achieve the 160F boiler return temp. As system return temp increases, the valve can be set to allow less boiler output to flow to the Termovar, and if system return temp is 160F or above, the valve can be set to allow no flow to the Termovar, thus allowing all flow to the system and no flow through the Termovar. If too little boiler output hot water is allowed to the Termovar, system return temp will fall below the target of 160F.

The ideal would be a valve that automatically "precisely" achieves the target boiler return water temp, thus maximizing system flow at all output temperatures. As a practical matter, I think the limiting valve generally can be "set and forget it" based on average system return water temp. If actual boiler return water is +/- 160F by some amount, I doubt there is very much system impact.

Some say that boiler return water may be as low as 140F. Although, experiments I have done pretty clearly show that maintaining boiler return water at 160F improves boiler btu output. The hotter water around the firebox improves combustion, produces more wood gas, and therefore increase boiler btu output vs a lower boiler return water temp.

Personally, I set the limiting valve to target 150F minimum boiler return water, and then allow return water temp to rise as system return water temp increases. I don't mess with the limiting valve very much.

 

[jebatty]

I repeated the data check on Termovar operation on which I did a quick check yesterday. Here are the results.:

Set the Termovar limiting valve (also might be called a diverter valve or balancing valve) open to result in 160F+/- return water to the boiler:

Boiler return: 158F
System return: 141F
Boiler supply: 177F
Approx gpm: 4.5

Set the Termovar limiting valve fully open so no restriction on boiler feedback flow through the Termovar:

Boiler return: 165F
System return: 142F
Boiler supply: 178F
Approx gpm: 2.5

Note that system flow increased 80% by proper adjustment of the limiting valve to only provide the needed boiler return water protection of 160F+/- instead of no flow restriction through the Termovar.

Charge storage tank to result in 160F+ system return; set the Termovar limiting valve at the same setting which resulted in 158F boiler return as noted above:

Boiler return: 187F
System return: 187F
Boiler supply: 190F
Approx gpm: 7*

With system return 160F+, fully close the Termovar limiting valve so no boiler feedback flow through the Termovar (no boiler return water protection needed):

Boiler return: 187F
System return: 187F
Boiler supply: 190F
Approx gpm: 8.75*

Note that system flow increased 25% by fully closing the limiting valve and bypassing the Termovar when system return was 160F+.

Two important conclusions:

1) A Termovar limiting valve will materially enhance system performance (achieve increased flow) if it is adjusted to provide 160F boiler return water protection rather than no limit on boiler feedback through the Termovar. Measurement of actual boiler return water temperature is important to determine this adjustment.

2) When system return exceeds 160F, the limiting valve may be fully closed to provide no boiler feedback through the Termovar and system performance will be further enhanced (increased flow).

Comment: the data applies directly only to 160F boiler return water protection. The data likely will produce different results at lower settings of boiler return water protection.

* My system boosts flow when boiler supply temp reaches 188F; flow boost is cut when boiler supply falls to 185F. This flow boost nearly eliminates all boiler idling at the high end of storage charging. Since the flowmeter producing the gpm readings adds about 2 psi to system head, I normally operate the system with the flowmeter bypassed, and my actual flows therefore are greater than shown.

 

[Gooserider]

It almost sounds like you need some sort of Thermal expansion controlled valve on the Termovar boiler supply line, controlled by the temperature on the boiler return line...

Have it open pretty wide at low boiler temps to get fast warmup on the boiler from a cold start, but start closing down as the boiler return temps got higher and you need less mixing at the Termovar... It would seem like it would work, but what I don't see is why they couldn't build this sort of functionality into the Termovar in the first place - seems like it wouldn't be that hard to just make it so that the thing would simply shut the boiler supply line off completely as it gets hot - seems like the loading units do this, why can't the simple valves?

Gooserider

 

[jebatty]

This functionality is built into the Termovar, but not as well as it might. The valve does start wide open on the boiler supply side when the return side is cold, and it does not allow any system return until boiler supply reaches about 160F. Then the valve opens on the system return side and closes partially on the boiler supply side. It's just that it could close down more on the boiler supply side without relying so much on the manual limiting valve to limit boiler supply flow through the valve when return water is 160F+ and no boiler return water protection is needed.

In practical terms, it still is not a big deal. The valve does provides boiler return water protection, which is very important. Because of my storage and how I use my system, which ranges between a low of about 100F to a high of 190F on system return (storage tank depleted to storage tank fully charged), I've learned a reasonable setting for the limiting valve on a "set it and forget it" basis. If a person has a more consistent system return temp, then it would be even easier to get the "right" setting for the limiting valve both to provide required boiler return protection and to maximize system flow.

Wouldn't it be useful if a Termovar engineer chimed in and explained the reason for the design being what it is, if there is a reason, or to simply state that the design is not as good as it could be?