What GPM do you run

[MR P BODY]

I just got my boiler fired up for the first time today...
its working great... but with adjusting the zones I can
change the the flow rate.... what do you guys like to
see and what would be your minimum flow (GPM). I have
the 1/8 HP pump with a Takagi JR boiler. I'm heating 1100
sqft of concrete, insulated.... I'm set at 2.4 GPM right now
140 out temps and 80 return
Thanks

 

[redsky49]

That's a substantial temperature drop, especially since we have not entered winter max heating yet.

While knowing absolutely nothing about your system (so take this accordingly), I would suggest that the flow rate be increased and observed for performance - particularly for overall equal heat distribution. There is also the possibility of "thermal shock" that can occur when the entering temperature to the boiler is too low. You may also experiment with a lower leaving temperature. Maybe drop the temp down to 130 and see what happens. There is a happy medium between temp and flow rate and often
it takes a while to find the best balance.

Unless you are building cookie cutter houses (or MacDonalds), all projects such as this are prototypes. There is a period following completion of the systems known as "commissioning". During this period, the final tests and adjustments are made to the system and oftentimes small "tweeks" are required. This allows you to optimize the system performance, and most systems are not anywhere near optimized at completion of construction. Mark all final valve settings, bleed the air, check the expansion tank, confirm operation of safety devices, measure flue gas temp, verify provision for pipe expansion, confirm temperature settings for automatic temperature comtrols, etc., etc.

By the way, exactly how are you throttling the flow? How do you determine (measure) flow rates? Do you have instrumentation? Can you record performance over time?

As always, offered only as opinion

 

[chevelle67]

According to the numbers you posted and assuming you actually measured the GPM and got 2.4, your boiler is providing 72,000 btuh. What is the boiler rated for?

 

[MR P BODY]

I have a meter that monitors the output temp from the boiler, input (return to the
boiler) and a flow meter.... I have valves on both the inlet and return on each zone
JUST in case a zone were to develop a leak.... so far I've slowing down the return to
hold the heat longer in the floor... todays temps are higher on the return... up to 94
and the floor is nice and warm... during the night it was cycling the boiler on and off,
it was up to the temp I set it at (62*). All the safety equipment is working great

 

[nate379]

Do you have a mixer valve? My setup keeps the out and in water about 30-40* difference usually.

 

[redsky49]

For others who may be following this thread, you can calculate the heat output of any system by the following formula:

Flow (GPM) x TD (temperature difference, supply and return) x 500 = Btuh

Note that this number does not address boiler efficiency.

Assuming that there isn't something else going on in the system, you are currently providing 65 btu per sq. ft. heating. This is a pretty high number (unless you live next door to Nate379 in Alaska). For a system start up of a cold system, this number may be appropriate. For continual operation, it seems pretty high, assuming that the space is well insulated. Again, however, I do not know your location or heating requirements.

The "thermal lag" of a radiant system (sometimes referred to as the thermal flywheel effect) may also affect your first impressions. It likely would take at least a day to bring a cold slab up to design temp. Once steady state operation of the system has been achieved you will be better able to judge the performance. [One of the nice features of a radiant slab versus forced air heat is that you can briefly open a garage door without the loss of a great deal of stored heat].

Suggest that you allow the system to operate as currently configured for a period of time to establish a baseline. Make any system changes one at a time and record the result.

I am also not familiar with your boiler manufacturer. See how low the boiler can safely go regarding leaving water temp. Many boilers, such as for Hot Water Baseboard, may use much higher temperatures than are required for radiant floor slabs. Do not exceed the operating parameters of the boiler.

As stated earlier, these systems take some time (and effort) to optimize. A spot metering infrared measuring device will prove useful for monitoring slab temperatures, as well as the performance of your wall and ceiling insulation.

Keep us informed as to how the system performs.

As always, offered only as opinion

 

[nate379]

To give you an idea I heat roughly 2000 sq feet between the house and the garage and my domestic hot water with a 105,000btu Burnham boiler.

 

[chevelle67]

Truth is you sound like you have a pretty good grasp of what your doing. You are going above and beyond what most people do. I figured 72000 btuh using a very basic formula, you can experiment with flow rates and plug the numbers in yourself to get the best results. There are some very accurate calculations that can be done that take into account hysteresis of the slab, as well as actual combustion eff and transfer losses but we use those when setting up paper mills, power plants etc. generally 1,500 boiler horse power or more, or on smaller process equipment when customers request it.