Measurement of Refrigeration Capacity

[ck10]

Dear all,

I've been tasked to evaluate the COP of an existing ammonia refrigeration plant and as a newcomer, I would like to seek advice on how I could actually proceed.

Parameters which I would be able to obtain are the suction and discharge pressures of the compressor and the compressor motor power. I understand that I should measure the mass flow as well but unfortunately I do not have the tools to measure the mass flow of ammonia.

I would probably be able to estimate the mass flow at full load capacity from the specifications based on the condensing and evaporating temperatures, but I'm not sure on how the mass flow would vary with capacity in a reciprocating compressor. would it be reasonable to assume the power is related to the capacity in a linear relationship?

I understand my questions are amatuerish and I realize I have much to learn on refrigeration. Thus I would deeply appreciate if anyone could point me in the direction in which I could measure the refrigeration capacity / COP of ammonia compressor.


Thanks.
CK

[Toosh]

Dear all,

I've been tasked to evaluate the COP of an existing ammonia refrigeration plant and as a newcomer, I would like to seek advice on how I could actually proceed.

Parameters which I would be able to obtain are the suction and discharge pressures of the compressor and the compressor motor power. I understand that I should measure the mass flow as well but unfortunately I do not have the tools to measure the mass flow of ammonia.

I would probably be able to estimate the mass flow at full load capacity from the specifications based on the condensing and evaporating temperatures, but I'm not sure on how the mass flow would vary with capacity in a reciprocating compressor. would it be reasonable to assume the power is related to the capacity in a linear relationship?

I understand my questions are amatuerish and I realize I have much to learn on refrigeration. Thus I would deeply appreciate if anyone could point me in the direction in which I could measure the refrigeration capacity / COP of ammonia compressor.


Thanks.
CK

Hi This stuff is freely available in GOOGLE
http://www.nt.ntnu.no/users/skoge/bo...oniaReport.pdf

use it in future

Norm

[ck10]

Hi Norm,

Thanks for the link. Digesting the information now.


Best regards,
CK

[Segei]

Hi This stuff is freely available in GOOGLE
http://www.nt.ntnu.no/users/skoge/bo...oniaReport.pdf

use it in future

Norm

This is theoretical research. I don't think that it can be useful for practical application.

[Segei]

Dear all,

I've been tasked to evaluate the COP of an existing ammonia refrigeration plant and as a newcomer, I would like to seek advice on how I could actually proceed.

Parameters which I would be able to obtain are the suction and discharge pressures of the compressor and the compressor motor power. I understand that I should measure the mass flow as well but unfortunately I do not have the tools to measure the mass flow of ammonia.

I would probably be able to estimate the mass flow at full load capacity from the specifications based on the condensing and evaporating temperatures, but I'm not sure on how the mass flow would vary with capacity in a reciprocating compressor. would it be reasonable to assume the power is related to the capacity in a linear relationship?

I understand my questions are amatuerish and I realize I have much to learn on refrigeration. Thus I would deeply appreciate if anyone could point me in the direction in which I could measure the refrigeration capacity / COP of ammonia compressor.


Thanks.
CK

You should go to compressor manufacturer and ask for compressor engineering data.This is information about power use and capacities at different condensing and suction pressures.

[mad fridgie]

What are you cooling, is a liquid or are you chilling rooms.
If liquid it is easy (flow*td*specific heat)/power in = COP, I would do this over a long period to give you an average.
If load is not known, (rooms are variable) then install flow meter in liquid ammonia, measuring and recording system temps/pressures.
Calculate nett refrigeration effect/power in. Again do over time to give averaged COP.
Then base the actual verses therory.
If large difference the possible comp problems (worn valves etc).
Also are you including all other power users, water pumps, fans etc. This could give a wide swing in COPs especially in low load situations.
It is all about time and money, the more you but in the better the result

[Segei]

I didn't see any plant with ammonia flow meters.
Compressor problem. Discharge temperature will jump if discharge valves leak. Suction valves leak will reduce energy use. Compare current energy use at certain operating conditions with compressor engineering data from manufacturer.

[mad fridgie]

I didn't see any plant with ammonia flow meters.
Compressor problem. Discharge temperature will jump if discharge valves leak. Suction valves leak will reduce energy use. Compare current energy use at certain operating conditions with compressor engineering data from manufacturer.

You can get a flow meter for just about any material.
To calculate COP of a system you need to know your load (the bit you are cooling) In rooms this is quite difficult (practically hugh variables) By knowing the actual mass flow of the refrigerant and the conditions it is at, you can calculate refrigeration effect, if you then remove system losses either by detail measurement or theoretical calcs you will end u with nett refrigeration effect. (how detailed to determins accuracy)
Damage to compressor parts valves, rings etc, effect volumetric efficiency, which inturn effects actual mass flow, thus makes changes to power draw (COP)

[Segei]

You can get a flow meter for just about any material.
To calculate COP of a system you need to know your load (the bit you are cooling) In rooms this is quite difficult (practically hugh variables) By knowing the actual mass flow of the refrigerant and the conditions it is at, you can calculate refrigeration effect, if you then remove system losses either by detail measurement or theoretical calcs you will end u with nett refrigeration effect. (how detailed to determine accuracy)
Damage to compressor parts valves, rings etc, effect volumetric efficiency, which inturn effects actual mass flow, thus makes changes to power draw (COP)

Did you see any ammonia refrigeration plant with flow meters?
Theoretically we can do everything but practically.... Typically ammonia refrigeration has a few evaporative temperatures. You need flow meter for every temperature. To compare apple and apple suction pressures and discharge pressure should be kept constant. Efficiency of the compressors should not be changed(no unloading for screw compressors). I didn't get about system losses. What do you mean?

[mad fridgie]

Did you see any ammonia refrigeration plant with flow meters?
Theoretically we can do everything but practically.... Typically ammonia refrigeration has a few evaporative temperatures. You need flow meter for every temperature. To compare apple and apple suction pressures and discharge pressure should be kept constant. Efficiency of the compressors should not be changed(no unloading for screw compressors). I didn't get about system losses. What do you mean?

Yes seen mass flow devices on ammonia!
These flow meters are normally coupled to computers and give real time readings, they also totalise (add up the total flow, like a water meter)
If a single plant (common refrigeration system)
then liquid flow is common, compressor suction pressure and temperature are common. You can calculate your nett refrigeration effect.
How you record the data can determine if instantaneous performance is calculated or long term averages.
If you have a LT pot and a HT pot, then you need 2 flow meters and 2 sets of temp/pressure equipment.
Let the compressor unload. we are measuring all, not a problem.
System losses, total change in enthalpy gives refrigeration effect, but not all the change is related to chiling the product/area.
Such as pressure drop down suction line and heat ingress to the suction line, to what level you go to is determided by the mighty Dollar, Euro, Pound, Yen etc. ( I sorted stated this already)
On a practical note the bigger the plant, the more worth while.
The original writer did not give size or application, only wanted to know how to do it.
He state that the comps were recips, so will have some for of wear and thus reduced performance.
The more actual correct info you have the more accurate your result.
I am certainaly not detracting the skill of a good engineer, I would rather have one of these than a computer. The combination complements each other.

[mad fridgie]

Yes use suction and discharge pressure and suction temp at compressor inlet and liquid temperature at the exansion device
You can input this into your manufactures comp details,
make note of power draw (and amps)
Client maybe paying for KVA not kW
Loading and unloading (force to 100% on controller) how manage your load to keep at required pressure maybe some what more difficult.
If a recip then you can leave unloaded and reduce capacity by % unload (power use would be by % slightly higher (rotating mass etc)

[jeremynh3]

COP (HP/TR) is difficult to quantify and using manufacturing data only gets you close. In general, you can assign efficiency to the original system design (single stage two stage sub cooling belts etc .

When I've been called to look at COP I look at the overall system design and installation. Bottom line is the cost to operate and maintain the equipment. Each industry has bench mark operating costs and what makes the owner or CEO happy is when they are below industry bench marks. Cost per cube or per pound however its tabulated.