| HVAC PRIME SOURCE, LLC |
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CHILLER TIPS
Chiller Tubes Freezing due to a Major Refrigerant Leak or Release
In case there is a major refrigerant leak or accidental release, it results in an uncontrolled cooling in the
condenser and evaporator due to rapid evaporation of the refrigerant, which tends to freeze the water in
the tubes. A major refrigerant leak or release can occur due to a catastrophic failure of a fitting, or failure of
a safety valve or rupture disc. If such a condition is encountered and the leak cannot be quickly isolated, the
chilled and condenser water flow through the chiller should not be shutdown, since the tubes become more
prone to freezing with standing water, which eventually results in tube breakage and flooding of the chiller.
In case there are other chillers operating in parallel, ensure that the flow does not reduce through other
chillers below the minimum required, due to flow being maintained through the failed chiller. It may be
necessary to reduce the flow through the failed chiller to a minimum (say 20% of normal) by using manual
balancing valves, such that flow through other chillers remains above the minimum required.
Refrigerant Charging Guidelines
Initial Charge -
The initial charge after complete evacuation of the system should always be done by the weight method. The
most accurate method is charging by weight. However, this can be done only after the Chiller or DX system
has been completely evacuated. The correct refrigerant weight for the initial charge can be found on the
nameplate or vendor manual. The weight of the refrigerant that is charged should be determined by using an
accurate digital scale. In case of split DX systems, the refrigerant charge specified by the nameplate or
vendor manual may have to be adjusted depending on the actual pipe lengths and fittings, based on vendor
guidelines or past experience.
Trim Charge -
In case the system already has refrigerant and needs a trim charge to make up for lost refrigerant due to
leakage or maintenance, the weight method is typically not feasible. Evacuating the refrigerant and
recharging is time consuming and typically not desirable in such situations. Following three methods are
recommended for an optimum trim charge to make-up for lost refrigerant, or remove refrigerant due to
overcharge –
1) LTD (leaving temperature difference) Method for centrifugal chillers –
(Ref. Carrier centrifugal chillers fundamental training manual SER120)
2) Sub-cooling Method for systems with TXV –
(Ref. Carrier Training Catalog # 020-066)
3) Superheat Method for systems with air cooled condenser and no TXV –
(Ref. Carrier Training Catalog # 020-066)
GENERAL NOTES:
Chiller Tubes Freezing due to a Major Refrigerant Leak or Release
In case there is a major refrigerant leak or accidental release, it results in an uncontrolled cooling in the
condenser and evaporator due to rapid evaporation of the refrigerant, which tends to freeze the water in
the tubes. A major refrigerant leak or release can occur due to a catastrophic failure of a fitting, or failure of
a safety valve or rupture disc. If such a condition is encountered and the leak cannot be quickly isolated, the
chilled and condenser water flow through the chiller should not be shutdown, since the tubes become more
prone to freezing with standing water, which eventually results in tube breakage and flooding of the chiller.
In case there are other chillers operating in parallel, ensure that the flow does not reduce through other
chillers below the minimum required, due to flow being maintained through the failed chiller. It may be
necessary to reduce the flow through the failed chiller to a minimum (say 20% of normal) by using manual
balancing valves, such that flow through other chillers remains above the minimum required.
Refrigerant Charging Guidelines
Initial Charge -
The initial charge after complete evacuation of the system should always be done by the weight method. The
most accurate method is charging by weight. However, this can be done only after the Chiller or DX system
has been completely evacuated. The correct refrigerant weight for the initial charge can be found on the
nameplate or vendor manual. The weight of the refrigerant that is charged should be determined by using an
accurate digital scale. In case of split DX systems, the refrigerant charge specified by the nameplate or
vendor manual may have to be adjusted depending on the actual pipe lengths and fittings, based on vendor
guidelines or past experience.
Trim Charge -
In case the system already has refrigerant and needs a trim charge to make up for lost refrigerant due to
leakage or maintenance, the weight method is typically not feasible. Evacuating the refrigerant and
recharging is time consuming and typically not desirable in such situations. Following three methods are
recommended for an optimum trim charge to make-up for lost refrigerant, or remove refrigerant due to
overcharge –
1) LTD (leaving temperature difference) Method for centrifugal chillers –
(Ref. Carrier centrifugal chillers fundamental training manual SER120)
This method is normally used for centrifugal chillers that have flooded evaporators.
- Determine the design approach temperature for the evaporator, i.e.the temperature difference
between the chilled water leaving temp and evaporator refrigerant temperature. This is the
evaporator LTD, and should be available from the OEM literature. In case it is not in the OEM
literature, use the normal baseline value based on past experience. - Measure the actual LTD for the evaporator.
- If the actual evaporator LTD is greater than design or baseline, add refrigerant. The LTD should
reduce on adding refrigerant if it was low. Continue to add refrigerant till LTD reaches the
minimum/design value and levels off. Adding more refrigerant after the machine has reached an
optimum charge will result in an increase in LTD, which is an indication of an overcharge and the
extra refrigerant should be removed till LTD comes back down, i.e.optimum charge is achieved
when LTD is minimized and levels off. - Also, monitor other parameters, such as condenser and evaporator pressure, which should be
close to the design value for an optimum charge.
2) Sub-cooling Method for systems with TXV –
(Ref. Carrier Training Catalog # 020-066)
- Determine the design sub-cooling value for the system, based on OEM literature.
- Determine the corresponding liquid line temperature and pressure using a sub-cooling calculator.
- If the actual liquid line temperature and pressure match with the calculator, the charge is ok.
- If the actual liquid line temperature does not match, add refrigerant to lower the temperature or
remove refrigerant to raise the temperature. - See referenced training catalog for details. The catalog and sub-cooling calculator can be
purchased from the Carrier website www.carrieruniversity.com under Training Materials.
3) Superheat Method for systems with air cooled condenser and no TXV –
(Ref. Carrier Training Catalog # 020-066)
- Measure the outdoor air db temperature, conditioned space air wb temperature, suction line
temperature, suction line pressure. - Use the superheat calculator to determine the required superheat based on the measured
indoor air wb temperature and outdoor air db temperature. - Use the superheat calculator to determine the required suction line temperature based on the
above superheat. - If the measured suction line temperature does not match the temperature from the calculator,
add refrigerant to lower the temperature, or remove to raise the temperature. - See referenced training catalog for details. The catalog and superheat calculator can be
purchased from the Carrier website www.carrieruniversity.com under Training Materials.
GENERAL NOTES:
- Typically liquid charging is done for the initial charge on the high side, and vapor charging is
done for the trim charge on the low side. - Always add the refrigerant in small quantities for a trim charge, and monitor the parameters
closely while charging. - Use accurate digital temperature instruments to measure the LTD and other temperatures for
the purpose of charging. Do not use the lollipop indicators installed on the machine, since they
are not accurate enough for charging purpose.
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