Vito Operation w/Indoor & Rad Temps

Mike T., Swampeast MO

A while back some asked for indoor and radiator temp measurements to correspond with a period of Vitodens operation. Did such Friday night.

Radiator temps taken at top/center of radiator; return temps taken at return union nut. Used the same thermometer (digital with wired remote sensing bulb) for all. Carefully cut a rather large piece of extruded polystyrene to fit around the sensing bulb and weighted it down with a heavy sledge hammer.

Some true curiosities. The family room, library, hall and dining room are all open to one another through wide openings. A single radiator in the living room provided nearly half the heat for the entire area and was the only radiator in the entire house with an average surface temperature over 100°.

One radiator had an average temperature lower than the return temperature--I triple checked. Its return connection is very close to the main, so I guess it must be conductive heat from the main.

One radiator and return was at ambient with the room even though the space must be loosing some heat--guess it's picking up heat from below and from the two adjacent radiantly heated bathrooms.

Radiator surface temperatures were generally so low (81° was the 2nd highest reading) that I increased the output estimate to 2 btu/hr per square foot EDR per degree of temperature difference between room air and radiator. Still used 1.5 btu/hr for the one radiator with an average temp of 103°.

Did my best to estimate actual loss with the proper correction for ambient temp of that space plus those surrounding, but such gets rather hairy... ±20% should be fair. Total estimated loss agrees reasonably with total estimated output. While I did measure all radiators, I only measure one of the four radiant baths.

Sorry, was only able to make return measurements on some of the radiators--the thermometer takes quite a bit of time to stabilize, ran out of beer and I was getting tired...

When it comes to delta-t and flow things get confusing. Boiler was consuming about 27 mbh during the period. If I say that 93% of input is available to the system (reasonable if not overly conservative for a Vitodens with return temp of 96°) the total system was using about 25 mbh.

With a measured (on surface of 1" black iron about 3' from boiler) delta-t of 14° that means a total system flow of about 3.6 gpm. With only the built-in circulator for flow and it operating at factory speed settings, I don't believe this flow rate is possible. If so, it must be nearly topped out and there would be no pump headroom available if I turn up TRVs. My previous response tests tell me that I have LOADS of pump headroom...

If I use the "boiler temperature" compared to measured return, delta-t increases to 25° and flow reduces to 2 gpm--much more realistic I believe.

Will try to repeat much of this if I have a much colder night with calm winds and the time to do the test.

Mad Dog

Thanks For sharing the experiement Mike

Mad Dog

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Mike T., Swampeast MO

You're welcome Mad Dog.

Honestly I was a bit shocked at how low the radiator temps actually were. Also did a "flimsy paper test" to get an idea of convection. Not surprisingly the only radiator that showed any movement of the paper was the one with an average temp of 103°.

Mad Dog

Me too but that is what experimenation is for

keep us posted. Mad Dog

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Mike T., Swampeast MO

Only substantial difference I can tell between new and old boilers (reset curve nearly identical) is the radiant baths. Previously the baths would run 5° above the average surround temps--now they run at 4° above.

Boiler has been set for 141° @ 8° outside with 0.8 ratio and room temp setting at 69°--unchanged for over a month. For a while the baths were running on 3°-4° above. I gave a bit of extra shift to the curve and it seemed to have no effect. Then I raised the room temp setting by 1° and everything seemed to stabilize at the 4° differential. I'm still not sure what those room temp settings do to the reset curve...