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Insufficient flow in radiant system (air removed via purge cart) looking for reasons?
To answer some questions on procedure.
I have the flow meters FULL OPEN
Adjustment to the run is done via the KEY NOT the Blue Adjustment Cap
ALL pumps are UPS 15-58 1 Main circulator 3 Zone Circulators.
There are 3 SS-Manifolds (see pic)
2 Are 8 Run ½” pex 250 feet +/-1%
1 Is 4 Run 1/2:” pex 250 feet +/-1%
ALL connections FEED and RETURN are ¾” pex from pump to manifold.
It has approx. 10 feet of connecting pex FEED and RETURN.
The other two zones are 40 feet and 70 feet away from pump FEED and RETURN.
The MAIN LOOP (Boiler,exp tank etc….) see pics is joined with 1-1/4” copper
It is approx 16 feet loop length.
This system was designed with country well water on property.
Rather than take a chance corroding system, I decided to use a closed loop.
I used and AXIOM MF200 System Feeder for my pressure/fill requirement on makeup.
When I first started system I used a purge cart
The main system was started up (call for pump start disabled) hose was connected to
Fill location and relief valve was left off (highest point of main loop.) hose attached and run back to purge cart. Ran system for 10 min. until filled and consistent flow.
NOTE: ALL Zone pumps were off.
Also water was prevented from entering or exiting zones. MAIN LOOP flow only.
Unhooked Purge cart and reattached relief valve and fill cap.
Started main system pump to circulate water. (MAIN LOOP only)
Zones are still isolated and pumps disabled.
AXIOM pres./fill is ON. Add water if needed. Pressure to 12psi.
Nice smooth operation (no crackle etc…)
Ran for 10 min. No Main flow meter to give reading. Assumed fine.
Pressure built to 12 psi, water was added (indicated by water line moving down in tank)
AXIOM turned off by itself and system continued to run with new settings for pres.
Turned off system and moved to manifold purge.
1hp pump in 53 gallons of clean water hooked to input of manifold on the FEED side.
On the RETURN side I attached a hose and ran it back to cart.
Pushed 2gpm through individual run on manifold and let run for 10 min.
Did each run on manifold individually. at same rate
Then ALL runs on flow meters read approx. 3/4gpm per run, STRONG AND STEADY
RAN for 10 min.
There should be no air left in the manifold system.
Turned off all Runs on manifolds at Feed and Return (Key and Meter)
Opened feed and return to MAIN LOOP.
Since I used shark bite fitting on OUT of pump and IN of Return manifold able to fill line by hand and reconnect.
LAST winter the system ran as follows.
Basement zone 8runs. 1 run ON 7 OFF ¾ to 1 gpm/ 8 run ON / flow by 8 (not readable)
Ended up using 4 outside RUNS down to 2 when it got cold.
Alternated other two zones which are upstairs and divided up runs to outside.
In other words, a lot of manipulation to keep house at 18C on cold days.
So you see I was hoping to have found my answer by now, but life has a way of getting in the way. So here I am back at it before winter starts.
I can get the same performance as last year but I need way better.
My problem assumes the following when sizing pump.
All circulator pumps are typically sized based on the heat load and head loss (pressure drop) for a given zone.
Knowing the heat load (in BTU's) for a given zone, allows to calculate the required circulator pump's flow rate in gallons per minute (GPM).
For hot water hydronic or radiant heating applications, the following equation can be used:
GPM = 0.002*BTU/(Temperature Drop, F),
where Temperature Drop is the difference between supply and return temperatures in the system and GPM is the amount of flow the circulator must produce.
Since most of the radiant heating systems utilize a 20F temperature drop, the formula can be changed to:
1 GPM = 10,000 BTU/hr,
meaning that for every 10,000 BTU's of heat load the circulator must output a 1 gallon per minute flow.
This system calls for 80,000 BTU/hr, circulator pump should have a minimum 8 Gallons Per Minute flow rate at a given pressure drop.
The next step is to calculate the head loss, or pressure drop in the system.
Head loss is associated with friction of the water against the internal surface of the pipes/tubing in the hydronic or radiant heating system and restricts flow rate a circulator can produce.
Although radiant heat manifold and PEX tubing sizing are a different topic, this systems manifold has 8 outlets with 1/2" PEX tubing installed at 250ft length per loop and the system calls for 80,000 BTU's.
Using the formula above, we can determine the flow rate required for our given zone: 80,000/10,000 = 8.0 GPM.
Flow rate through every selected circuit of the manifold equals Flow Rate divided by number of Circuits:
8 GPM/8 circuits = 1 GPM per circuit (assuming that the circuits are equally balanced).
Using a Pressre Drop Table or Pressure Drop Chart, supplied by the PEX tubing manufacturer, a pressure drop per ft of tubing can be calculated at a given GPM flow rate.
NOTE: Pressure drop data supplied by manufacturers may be available both in PSI (lbs per square inch) and in foot (ft) of head.
For conversion, I used the following equation: 1 psi = 2.3 ft of head (for fresh water), and 1 ft of head = 0.43 psi
In this example, pressure drop per 1 ft of 1/2" PEX tubing at 1 GPM flow rate would be approximately 0.03 ft of head).
Considering that each individual PEX tubing circuit is 250 ft long, pressure drop per circuit would be 0.03 x 250 = 7.5 ft of head.
Since PEX tubing circuits are in parallel to each other, pressure drop per circuit is always the same as the total zone pressure drop. So, the total pressure drop is: 7.5 ft of head
We now have the complete specification for the circulator pump available: 8 GPM flow at 7.5 ft of head pressure drop.
I understand that other components installed within a given zone (such as the radiant heat manifold itself, fittings, check valves, mixing valves, balancing valves, heat exchangers, PEX tubing length (different diameters), etc.) also have to be considered when sizing a circulator pump (see Scheme 1 below). Pressure drop information is usually available in a form of technical specifications or submittal sheet supplied by the manufacturer. Given real conditions, we may add extra 2 ft of head just in case, making pressure drop 9.5ft of head. NOTE: Pump head is a term used to describe the force the circulator develops to overcome pressure drop (pipe, fittings and valves). In a Closed System, "pump head" is NOT the height of the building. Height (on the Scheme above) is not taken into consideration. Regardless of this the zone manifold is below the pump, only rise is as pex comes out of top of pump to curve around and down to manifold. As per pics
The next and final step, is to match the obtained data with a correct pump on a Circulator Pump Curve Chart Which should be the Grundfos 15*58 on mid speed??????
But it is not the case.
Hope you can help, i'm not sure if the pump is functioning properly, from startup last winter it has never pushed what i had hoped it would. The previous system ran with same configuration giving me an output of 1/2 gpm per run, which works out to 4 gpm into manifold out of 15-58 pump. It was hooked to town water via a check valve.
Its not that it does not work, it is that it does not provide what the specs said it would.This system is on a pressure/fill tank which provides a system pressure of 12 psi on input to pump.
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