Calculating efficiency of hydronic distribution

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Old 10-18-15, 02:05 PM
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Calculating efficiency of hydronic distribution

Hi, everybody, I'm a newbie here so please forgive any gaffes. I'm in the process of trying to find out how well the old heat distribution system in my old historic home works. I already have a professionally done assessment of the efficiency of our boiler and measure the % fill of my propane tanks daily (adjusting to 60 degrees). In brief, there are four zones whose heat comes from a propane boiler. The lowest floor and the fourth floor have baseboards. The second and third floors have old-fashioned radiators. The pipe scheme is primary/secondary.

I have a datalogger with 2 k type thermocouples attached to the supply and return pipes from and to the boiler. As per a recommendation from a trusted source, they are located at least 10 pipe diameters from the respective inlets and outlets of the boiler and are attached on either side of the primary/secondary tees. I realize that these will not give the true temperature of the water inside the pipes, but my reasoning is that the delta between those two will give a decent estimate of how much of a temperature drop there is between the supply and the return. Is that a reasonable assumption? If not, could you explain? So, that's the first point.

I'm also using the datalogger, which is set for 10 second intervals, to figure out the actual flow rate in the pipes: when the supply temperature has its first spike after a call from a thermostat, I then look at the corresponding spike on the return side and time the difference. The interval between the two tells me how long it has taken for the ""pulse" of newly-heated water to arrive back home. Since I also know the length of pipe and the internal diameter, I can then figure out the actual gallons per minute , real-world, being pushed through. And, from this, the actual BTUs being delivered to the space. Any problems with this reasoning? Constructive criticism is more than welcome.
Later on, and I haven't gotten there yet, I am planning to measure the delta T's at the supply and return points for individual sections of baseboards and radiators to see if they are functioning anywhere near their design capacity.
Anyway I'm hoping for some knowledgeable folks to weigh in. Thanks for any responses.
 
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Old 10-18-15, 03:19 PM
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I don't have any pointers just yet, but questions.

What make/model boiler?

Are the four floors on separate zones?

Is there a 'reason' you are looking into this as deeply as you are?

Some problem you are trying to solve?

What is the goal?

The lowest floor and the fourth floor have baseboards. The second and third floors have old-fashioned radiators.
Are the baseboards CAST IRON? or FIN-TUBE?

The pipe scheme is primary/secondary.
Can you show us some pictures of the system?

I realize that these will not give the true temperature of the water inside the pipes, but my reasoning is that the delta between those two will give a decent estimate of how much of a temperature drop there is between the supply and the return. Is that a reasonable assumption?
Yes, I think so, as long as the TCs are well insulated on either side.
 
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Old 10-18-15, 05:07 PM
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I already have a professionally done assessment of the efficiency of our boiler
What were the results? What more info do you seek?

Are you are primarily interested in minimizing fuel costs? Is there any prospect of getting on natural gas instead of propane?
 
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Old 10-19-15, 06:04 AM
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Propane EK-1 with 120,000 K burner.

Yes, each floor has its own zone.

I suspect that the inefficiencies in our system are primarily due to the inefficiency of the distribution system.

I'd like to bring down our fuel bills which have been high and also reduce our carbon footprint. the energy audit we had done relied on assumptions concerning the distribution system and not actual measurements.

The baseboards are all fin-tube.

Right now the TCs are the velcro-warp-with-button type covered with electrical tape rated to 221. I'll add insulation around them to improve protection from the air temps. I have pipe-wrap and elastomeric.

Pix added showing a pano of the system and details of the TC on the supply side of the T, then the return side in that order.

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Last edited by NJT; 10-19-15 at 06:30 AM.
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Old 10-19-15, 06:28 AM
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If memory serves the combustion efficiency was between 84-86%.Checking with the provider but they haven't gotten back to me yet.
Basically, looking to find ways to cut down on our consumption in a way that's practical and gives reasonable return on investment.
Unfortunately, we can't get natural gas in our area. I've checked with the local utilities - too far out in the country.
 
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Old 10-19-15, 06:36 AM
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I'll add insulation around them to improve protection from the air temps. I have pipe-wrap and elastomeric.
You want to extend that insulation at least a foot either side of the TC to reduce conductive losses.

What size are these pipes?

 
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