Slowing Down Flow

I'm trying to get my system down to a delta T of 20*. I have a shut-off valve on the return closed about 1/2 way and (2) adjustable flow valves (i think thats what they are) closed about 1/2 of the way. These valves are located on two separate loops of the same zone and are located just before these two loops become one and head back to the boiler. One loop serves half of my first floor, and the other serves the other side of the first floor and the loft. I was able to get my Delta T to around 12*, but no higher. I can hear the flow through the system now, which I do not like . The only other valves I have inline with the system are isolating the pump. I'm hesitant to close these at all, but figured I would ask here if that is an available option.

Thanks

Are you at design conditions?

What is outside air temperature?

What is supply water temperature?

What is so magical about slowing flow down to get a 20 deg. delta t?

BTW, most hydronic systems do not operate at exact perfect conditions but still work just fine.

Hollyfeld wrote:These valves are located on two separate loops of the same zone and are located just before these two loops become one and head back to the boiler. One loop serves half of my first floor, and the other serves the other side of the first floor and the loft.

Does your system look like this?



I'm pretty sure the two valves you are talking about are intended to balance the flow through each half of the loop. I would adjust those first and to get things balanced...then adjust the valve on the output side of the circulator to restrict the flow through the entire zone. Recheck your supply & return temperatures and adjust as necessary.

A few other thoughts. Make sure you are getting accurate temperature readings. Strap-on pipe thermometers can be very inaccurate if they don't make good contact with the pipe.

Have you calculated the actual heat load on this zone? How much flow is required? What size is the piping? What are you using for a circulator? What temperature was it indoors and out when you did this test? Boiler temperature?

Edit: Steamup beat me to it.

That is what my system looks like. When you say get them balanced, are you talking about getting heat from both of those loops or actually getting a better Delta T from them?

I have never done a heat loss calculation on my house. I have an existing 114k BTU oil boiler that I never had an issue with keeping the house at any temperature. When my K6 was installed the balancing valves were moved from their original position for reasons I do not recall or know. No other changes to the system were ever made. I'm under the impression that a greater delta T than what I am getting would result in more heat being transferred into my living space.

I do have strap on thermometers and the temperature readings on them seem to be accurate to at least balance a system.

Outdoor temps - vary, but when its down in the single digits, my house does not stay at temperature (68*)
Supply temp - usually between 165 and 180.

There was a cold snap a few weeks back into the single digits. My thermostat was set at 68*. Boiler temp around 175 and stoking. House temp was down to 63*.

Information I need to get:
Pump info
Pipe sizes

Hollyfeld wrote:That is what my system looks like. When you say get them balanced, are you talking about getting heat from both of those loops or actually getting a better Delta T from them?

I have never done a heat loss calculation on my house. I have an existing 114k BTU oil boiler that I never had an issue with keeping the house at any temperature. When my K6 was installed the balancing valves were moved from their original position for reasons I do not recall or know. No other changes to the system were ever made. I'm under the impression that a greater delta T than what I am getting would result in more heat being transferred into my living space.

I do have strap on thermometers and the temperature readings on them seem to be accurate to at least balance a system.

Outdoor temps - vary, but when its down in the single digits, my house does not stay at temperature (68*)
Supply temp - usually between 165 and 180.

There was a cold snap a few weeks back into the single digits. My thermostat was set at 68*. Boiler temp around 175 and stoking. House temp was down to 63*.

Information I need to get:
Pump info
Pipe sizes

Actually, the greater the delta t on a loop, the less the heat transfer. Heat transfers from the water to the air. High to low. The hotter the water or hotter the average temperature, the greater the heat transfer. The greater the delta t, the lower the average water temperature and the lower the overall average heat transfer. Typical design for finned tube is 20 deg delta T. If design hot water temp is 180, then 160 would be the return and finned tube sized on 170 deg. average water temperature. If you have a smaller delta t than 20, it just means that the flow is greater than what a 20 deg delta t heat loss from the radiation would dictate.

If your house is not up to temp, the problem doesn't lie in the flow. The radiation need to be check to make sure air flows through it ok.. IE, nothing blocking it such as curtains, damper closed, dust on fins, too many doggy toys stuffed under it, couches too tight to wall, etc.

Maybe the fin length is too short for the heat loss. Up your water temperature in the colder weather if you have to.

Btu's per hour = GPM x 500 x Delta T. You can decrease the flow, increase the delta t, and still deliver the same amount of heat . I suspect something else is going on here.

I remember you trying to troubleshoot this before. What happens if you try to do the same job with the oil boiler?

Rob R. wrote:Btu's per hour = GPM x 500 x Delta T. You can decrease the flow, increase the delta t, and still deliver the same amount of heat .

Only if the heating devices have the capability of removing the heat at a lower average delta t.

180 to 160 is an average of 170 deg water temp. Typcial Residentail finned tube might output 700 btuh/ft at this temp.

Slow the flow down and get a 30 deg. delta from 180 to 150 with an average 165 deg water temp, typical residential finned tube might only output 655 btuh/ft at this temp. You would need more finn or a higher entering water temperature to compensate for the lower heat output.

Rob R. wrote:Btu's per hour = GPM x 500 x Delta T. You can decrease the flow, increase the delta t, and still deliver the same amount of heat . I suspect something else is going on here.

I remember you trying to troubleshoot this before. What happens if you try to do the same job with the oil boiler?

I know... I've have basically accepted that my K6, which is 30k BTU larger than my oil boiler, just can't keep up. I lived for 6 years with the oil boiler keeping my house at temp without any issues other than running out of oil. I clean and vac out the baseboards on a yearly basis and here I am scratching my head.

steamup wrote:

Rob R. wrote:Btu's per hour = GPM x 500 x Delta T. You can decrease the flow, increase the delta t, and still deliver the same amount of heat .

Only if the heating devices have the capability of removing the heat at a lower average delta t.

180 to 160 is an average of 170 deg water temp. Typcial Residentail finned tube might output 700 btuh/ft at this temp.

Slow the flow down and get a 30 deg. delta from 180 to 150 with an average 165 deg water temp, typical residential finned tube might only output 655 btuh/ft at this temp. You would need more finn or a higher entering water temperature to compensate for the lower heat output.

Perhaps then the answer is to anticipate the coming cold temps and ramp up the temps?

Upping the temps would be a good experiment. The K-6 would be slower to respond than the oil boiler.

Also, If you have the k-6 piped as per the manufacturer's recommendations with the bypass, the water is blended at the output of the boiler and the bypass. Even though the boiler is at 175, the hot water supply will be lower due to return water bypassing the boiler and blending with the supply water. You can compensate for this with the boiler turned up in colder weather.

steamup wrote:

Rob R. wrote:Btu's per hour = GPM x 500 x Delta T. You can decrease the flow, increase the delta t, and still deliver the same amount of heat .

Only if the heating devices have the capability of removing the heat at a lower average delta t.

180 to 160 is an average of 170 deg water temp. Typcial Residentail finned tube might output 700 btuh/ft at this temp.

Slow the flow down and get a 30 deg. delta from 180 to 150 with an average 165 deg water temp, typical residential finned tube might only output 655 btuh/ft at this temp. You would need more finn or a higher entering water temperature to compensate for the lower heat output.

I guess I was only looking at the math...if you reduce the flow and the delta widens enough, the end result can be the same...but in practice, it probably won't be. The heat output of the baseboards isn't linear with temp, so your point makes perfect sense.

What are the baseboard starting and ending temps?...

Even though the boiler is at 175, the hot water supply will be lower due to return water bypassing the boiler and blending with the supply water. You can compensate for this with the boiler turned up in colder weather.

Perhaps the bypass is cooling the output too much to hit the design temps...

There is no bypass installed.

CapeCoaler wrote:What are the baseboard starting and ending temps?......

any baseboard? I might be able to measure this!

If the system worked before and all you did was change the boiler and the new boiler has enough capacity, then something happened in the install.

Air bound somewhere?

Pump - what make/ model?

One loop much shorter than the other causing short circuit of flow?

Lower boiler setting - what was the oil operating at?

What is your coal boiler aquastat settings?