BMS reading for chiller

[bundy]

hi,
does any experience this problem before :
On the BMS/BAS monitor screen, the chiller tonnage is X ton. but when i used the formulea
ton= (16*flow(l/s)*Delta T)/24, the value is often different ?
This is due to equipment calibration out. I yet to ask my BMS guy wat wrong ?
Is there a standard algorithm for chiller sequencing using the tonnage.

 

[lilliput1]

Your equation will be correct if the temperature difference is in °F, not °C. If in °C you have to factor by 9/5. You must use the GPM & temperature sensed by the BMS.

 

[SilFox]

Hi bundy!
1. The real chiller's capacity can vary depending on loading.
2. Try to use the following formula:
TR = Flow(l/s) x Evap.Range(deg C) x 4.187 x 0.2844

 

[bundy]

hi sifox,

just need to clarify something, what does Evap.range stand for ? evap refigerant temp ?

thanks.

 

[quark]

Diff. between chilled water inlet and outlet temperatures.

 

[lilliput1]

Bundy's formula x 9/5 should equal Silfox but Silfox should review the constants because the product should be = (16x9)/(24x5)

 

[VSSriram]

Q = m x Cp x Delta T

Capacity in Btu/hr = Flow in GPM x 500 x Delta T in °F

 

[quark]

SilFox's formula is correct.

Heat removed Q(kJ/sec) = m(kg/sec) x Cp(kJ/Kg⁰C)xdT(⁰C)

1 kg water occupies about 1 liter volume

so Q (kJ/sec) = flow(l/s) x 4.18(kJ/Kg⁰C)xdT(⁰C

1 Ton = 3.517kJ/sec

therefore Q(ton) = (flow(l/s) x 4.18(kJ/Kg⁰C)xdT(⁰C)/3.517
= (flow(l/s) x 4.18(kJ/Kg⁰C)xdT(⁰C)x0.2843

Regards,

 

[lilliput1]

We are chasing decimals. All the above formulas are correct when rounded off, providing the correct units are used as noted above.

I am used to using Tons = GPM x 500 x (°F TD)

 

[lilliput1]

Correction Tons = GPM x 500 x (°F TD) / 12000

 

[ChasBean1]

Is the BMS guy using flow and dT to calculate tonnage? He might be using the chiller load value off the chiller panel. Just a thought.

 

[psighi]

If the system is sophisticated enough to have a BACnet interface with the chiller, the chiller will provide for a tonnage variable from the chiller panel. If you are observing the remote temperature and flow meter sensors in your EMCS, that calculation will be based on the EMCS sensors and you are comparing that to the chiller.
The chiller is reading a completely different pair of sensors than your EMCS mounted sensors.