A flow rate question?
A flow rate question?
(OP)
Hi all,
I'm trying to work out the flow rate for a pump to heat a chicken house. The farmer has already laid pipe and wants to size a pump. Its a two pipe system, feed and return with 5 water to air heat exchangers Link. He appears to have the first two in parallel, the next two in parallel and the last one on its own. Water flow-through is given as 1.76 m3/h for the exchanges, should i be aiming at a flow of twice this so that the first 4 get the required flow with the last one getting double?
I'm trying to work out the flow rate for a pump to heat a chicken house. The farmer has already laid pipe and wants to size a pump. Its a two pipe system, feed and return with 5 water to air heat exchangers Link. He appears to have the first two in parallel, the next two in parallel and the last one on its own. Water flow-through is given as 1.76 m3/h for the exchanges, should i be aiming at a flow of twice this so that the first 4 get the required flow with the last one getting double?





RE: A flow rate question?
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: A flow rate question?
RE: A flow rate question?
You seem to be saying that each set has its own pump? In that case and you want to make each pump the same then yes, 2 x for the parallel units and double flow for the single unit. This is why we need a diagram.
Of course the real issue is how to control and adjust the heaters so that each one get 1.76m3/hr and not , say, 3m3/hr
A diagram with lengths and pipe sizes is essential to work out what the pressure drop will be for the worst case and then add some control valves in the other lines / heaters
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: A flow rate question?
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: A flow rate question?
RE: A flow rate question?
The person who decided that 5 heaters is required is the one to ask.
RE: A flow rate question?
a) Size all supply and return lines with similar psi/100ft.
b) Add an RO on each supply line sized to produce a minimal dp at desired flow and include pressure taps at suitable distances from RO
c) Add a manual gate on each line to throttle to suit
During commissioning, set the hot water flow for each air heater by adjusting the gate on each line to get to target dp across the RO.
Some allowance on total pumping flow may be useful, say 10% of design = 1.1 x 1.8 x 5 = 10m3/hr. Some margin on controlling case dp for the pump would also be useful.
RE: A flow rate question?
The hot water - air heater coil passes should also be freed from trapped air - a vertical orientation ( as shown in the photo ) makes this difficult.
RE: A flow rate question?
Another way is based on equal exit temps for hot water from each heater - use a portable IR temperature gun to read off exit water temp by measuring pipeskin temp, and adjust the gate valve to suit.
RE: A flow rate question?
LittleInch and georgeverghese, i would say your guys are right, it would be 5 times the requirement plus 10% allowance to be safe.
RE: A flow rate question?
b) Add this throttle valve to each unit ( not to be doubled up as an isolation ) and have it set in a fixed position.
c) How are you going to manage temp control in this chicken shed (1)vary pump flow ( through a supply to return bypass valve) or (2)vary pump speed or (3) vary hot water feed temp
do you intend to automate this
d) What kind of pump is this - flow is low at 10m3/hr
e) Where is the expansion drum / degasser - is the feed nozzle to this at a higher elevation than all the piping and heaters ?
Main risk is air traps in the piping that may create high discharge pressure and choke up your pump
Okay if you are using the horizontal version 3H - check that exit nozzle is at higher elevation than the inlet so air gets to flow out of the coils.
RE: A flow rate question?
Most major pump vendors offer low flow centrifugal pumps. That may be a good place to start.
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: A flow rate question?
You should have balancing valves and an expansion tank with an air bleed on the high point.
RE: A flow rate question?
To set your system up you probably want to do this by checking temperature in and out is equal when all five fans are working.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: A flow rate question?
RE: A flow rate question?
Mono ethylene glycol is slightly toxic while PPEG is not, but PPEG - water has a higher viscosity and higher first cost. No flash point concerns with MEG.
For example, a 50% wt MEG - water mix is good down to -25degC or so, but viscosity is much higher than water as we go cooler, so if the pump needs to be started from cold, then the one of the operating cases for head at the pump may be something like 50% of 10m3/hr at startup from cold for more viscous MEG solution.
Other transport properties for MEG solutions will need to be accounted for. Use demin water to make up the solution and the Perry Chem Engg Handbook says add "inhibitor", but it doesnt say what type.
RE: A flow rate question?
RE: A flow rate question?
Presume you are aware that MEG solution rates will need to be higher than 1.8m3/hr to get the same heating loads, and hence unit dp will be higher also. The light duty flow balancing gate valves should do - wont need flow controls. Good luck
RE: A flow rate question?
RE: A flow rate question?
RE: A flow rate question?
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: A flow rate question?
RE: A flow rate question?
The loop pressure is generally maintained at slightly above atmospheric so there is never any oxygen present in the closed loop system.
The use of nitrogen in a place like this would most likely considered to be a safety hazard.