Heat Loss Calc, Radiator Temps & Vitodens

Mike T., Swampeast MO

Temp hovering a bit above freezing (actually a <I>very</I> slow drop all day) with completely overcast skys. Light wind. Cold, heavy rain for much of last night.

Boiler target and surface measured supply temp in near perfect agreement at 107F.

Estimated loss increased to about 25 mbh. Boiler operating at or very near minimum input of 25 mbh. (Only clocked once.)

TRV settings unchanged--indoor temp unchanged as well with the normal fluctuation of about plus-minus 1 F.

Three rads mentioned STILL the only ones with any heat. Remaining rads and associated branch lines stone cold. Did measure temp of only one "stone cold" rad and it was ambient. Used my hand for the rest. One rad <I>might</I> have been a touch above ambient, but its' supply branch still felt cold.

I realized that ALL THREE of the rads are served by the same main pair. That main pair and branch lines in the basement are fully insulated. Only thing with output from the other pair is the radiant shower floor at the very end. This 2nd main pair is intentionally uninsulated where it passes through the basement garage. Supply main there felt only slightly warm. Return stone cold.

Kitchen rad 97.3; hall rad 99.5; office rad 74.

I won't bother with the math for the iron rad output--loss is higher, rad temp is lower so output is actually higher!

Something is VERY WRONG!

Mike T., Swampeast MO

Attn: Steve Ebels

Just realized that I "accidentally" made GREAT test conditions this last week...

My drywaller FINALLY arrived to finish (I'd hung) the ground floor. VERY open floor plan and I don't even have drywall hung around the interior stairway to the basement. There's also a second open stairway leading into the master suite upstairs.

Drywaller complained that it was too cool. I'd been ready to put the boiler in "standby" and used my forced air occasionally in occupied space. I didn't want to go to too much trouble so just raised TWO TRVs slightly and raised the sun dial from 63° to 75°. One radiator in the kitchen where he's working, the other in the central hall.

Average space temp downstairs rose a whopping 2°F from 59° to 61°. No full-time occupation on the two lower floors currently (except me in the office--day, nights--never know--plus the rest of the house when I'm doing "real" work) so I lowered TRVs in the rest of the master suite to minimum to.

Drywaller said the place was still a bit cool when he arrived, but "perfect" after he started working. My office (the only other rad in the house currently above minimum) also jumped about 2° average without changing the TRV setting. Remember how I mentioned the slight "relativity" of TRVs when they're barely being supplied and then you give a significant boost in supply temp?

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Anyhow Steve, your ongoing post about "heat loss" made me decide to measure some temps while I was downstairs doing woodworking.

Am doing these calcs in real time, but believe the results will be truly amazing...

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First, my estimate of heat loss under current conditions:

20 MBH (this is 80% of the HVAC-Calc value).

1.75 MBH for the office, 18.25 MBH for the rest of the house.

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Boiler running 120 minutes on, 80 minutes off--minimum input (25 mbh). "Pulsing" for more than half of the "off" period.

So... Running at minimum 60% of the time or about 15 mbh. Not unreasonable that the "pulsing" is supplying the "missing" 5 mbh.

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Now the fun! Remember--I'd only raised TWO TRVs slightly. I felt, measured and double-checked a few at different times. Those two (plus the one in my office) are the ONLY radiators providing any heat!!! All the rest are AMBIENT!

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Weather turned cooler on Friday--it's Monday now. Some wet snow this morning. Completely overcast with 40° a decent "average" temperature for the period. Moderate wind from the N to NE.

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Those TWO RADIATORS downstairs have 162 sq.ft. EDR between them.

With a loss of 18,250 btu/hr associated with these radiators, this means that each square foot is giving off 113 btu/hr.

The radiator temp? Both 92.5°F (measured top dead center).

92.5°F rad temp - 61°F room temp = 31.5°F difference.

113 btu/hr output divided by 31.5° difference = 3.587 btu/hr for each square foot of EDR!!! That's more than DOUBLE the VERIFIED output of cast iron radiators with steam!!!

BUT, that's STILL not the whole story!!

Remember--the burner was cycling.

The 92.5°F was the MAXIMUM PRODUCED!!! After the burner had fired for about 30 minutes, BOTH radiators had achieved this exact same (with the same thermometer) temperature. While the measured system temperature continued to rise as the burner continued to fire, the measured radiator temp stayed the same!

Prior to the "burst" by the boiler, the measured temp of the kitchen rad was 82.2°F. The hall rad was similar in temp (measured with same model but different thermometer) but I caught the very beginning of the burst (unknown to me) when I kept checking the reading over a period of time. It felt just about the same as the kitchen rad...

SO, if I'm VERY GENEROUS and say that these radiators "average" 89° F over time they are now, on average, producing 4.03 btu/hr/sq.ft EDR!!!!

Someone, anyone, please tell me how this is in any way possible.

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Prior to changing the TRV settings and raising the sun dial, and under very similar outdoor conditions, boiler was running 60 minutes on, 120 minutes off (most of the "off" was actually "pulsing" of course). So...the setting change has DEFINITELY increased consumption.

jp_2

heatloss?

how are you calculating the heatloss of a room that is somewhat surrounded by colder rooms?

are the colder rooms always at a contant T?

Mike T., Swampeast MO

Heat loss calc for that one room already has a "cold wall" (5F lower) against both the interior hallway (only rad at the bottom of the big open two-floor stair hall) and the closet (10F lower) that partially divides it from the rest of the master suite.

Otherwise, it's a guesstimate based solely on the different room temps. Room directly adjoining this one room is 1F warmer than the rest of the house but I didn't compensate.

There are also three small baths with hydronic radiant floors but they were never even included in the heat loss--those (and the closets ALWAYS considered "cold partitions" but without loss and based on ACTUAL measurements) were my original "fudge factors". One big bath has electric radiant floor and hydronic radiant floor in the 3'x 8' shower--I removed its' loss for this estimate.

EVERYTHING has been maintained at the EXACT same TRV and boiler settings for 7+ days. I have not used the forced air electric WHATSOEVER.

Mike T., Swampeast MO

Forgot to say. Entire ground floor (with the two rads whose TRVs I raised slightly) averaging around 61°F. Have two datalogging thermometers down there--one fairly close to one of those rads, the other far away from either.

Office averaging 68°F. Master bedroom (adjoins office) averaging 62°F. Rest of upstairs averaging 61°F. Hydronic radiant baths on 2nd floor around 65°F.

I don't have datalogging sensors for every room, but I do have thermometers (most digital) in nearly all.

Office rad averaging around 72°F and steady in temp.

The two downstairs went from 82°F to 93°F during one heating cycle when I measured yesterday. Again, these were the ONLY three rads in the house above ambient! Two open staircases from ground floor to 2nd floor. One leads to a hall with doors normally closed save one. The other leads to a small hall opening into multiple rooms of the master suite. Both downstairs rads that are heated are near these staircases.

Mike T., Swampeast MO

The Gravity Mains

7 mbh from the mains reduces the radiator square foot output to about 2 btu/hr/sqft/°DT from the radiators.