Altitude Environmental Test Chamber Cascade HT R404a and LT R23

[Louis Joubert]

Hi Guys

I am currently calculating plant design for the refurb of an Altitude Test Chamber.
Chamber Spec is 150 degC to -60 degC. With Humidity control and Vacuum control.
We will be using a Jumo Imago 500 for temp, Hum and vacuum control.
Cooling done by refrigeration. Heating by elec heaters. Humidity by water spray, de-hum by HT de-hum coil refrigeration. Vacuum by Vacuum pump.

We will be using a cascade plant HT R404a and LT R23.

I have calculated the evap LT at -60 deg C 10.4 kw Tubed evap, no fins
Condensing LT @ -10 deg C ?
LT compressor Bitzer 4 CC 6.2

I the calculated the evap HT @ -15 deg C 20.58kw
Cond HT @ 40 deg C 31.9 kw heat rejection
Using a plate heat exchanger and calculated a flow rate of 1.547 l/sec with a 5 deg TD
HT compressor Bitzer 4 PC 15.2

I have seized the cascade condenser electric stepper valve from carel to E2V - 30.
Still awaiting Carel On R23 specifications. Valves, transducers ect.

I will be using Hot gas by-pass and liq injection to both stages for comp control.
I will be using a CPR for LT stage for pull down from high temp. Will set between 40 - 60 psi


My question is?

How do I calculate the Expansion tank?
How do I calculate the blow of valve?
is my -10 degC LT R23 Condensing optimum? was reading up and some say between -10 to -20 degC?
How do I calculate the captube for equalization between Hp and Lp of the LT system?
How do I calculate the captube between suction and expansion tank?

I would appreciate your advice a lot.

[corkman]

employ a designer

[Louis Joubert]

I was under the impression that there are a lot of experienced guys on this site?

[karma-john]

there is helping other engineers and there is giving info away that is doing a designer out of a job

[karma-john]

have you tried youtube

[karma-john]

how did you calculate the rest of it

[karma-john]

did you just use a programme as anyone can do that bit

[Louis Joubert]

I used common calculation formulas to calculate what i have.

I am not asking any designer to give away his job!

I was only asking advice in the way of calculating?

[Louis Joubert]

Is there any one that can give me usefull advice?

[Emmett]

Is there any one that can give me usefull advice?

First of all post #2 gave you very usefull advice!
Second, when you refer to a blow valve are you asking about a LT head pressure regulating valve (a valve which dumps the excess pressure from the discharge to the expansion tank)?
If this is the valve you are refering to then you won't need an equalization capillary, or one from the expansion tank to the suction side.
And calculating the expansion tank is difficult at best and I've seen some of the best in the business get it wrong, however common sense says that you would need to know the volumne of the entire system in order to calculate.
Good Luck!

[Louis Joubert]

Hi Emmett

The blow of valve I was refering to is not for LT is not for head pressure control. It is a safety device for worst case.

post #2 is very usefull I agree, unfortunatly its is very hard to get a designer who spesialize in this field where I am from. This is the reason I am on here and asking advice?

Do you have practical design experiance on the type of plants?

[Louis Joubert]

Hi Emmett

The blow of valve I was refering to is not for LT is not for head pressure control. It is a safety device for worst case.

post #2 is very usefull I agree, unfortunatly its is very hard to get a designer who spesialize in this field where I am from. This is the reason I am on here and asking advice?

Do you have practical design experiance on the type of plants?

The blow off valve will not be used for LT head pressure control, but for LT safety device.

[Emmett]

The blow off valve or pressure reliefe valve is installed to protect the entire system, therefore you have to determine which component has the lowest safe operating pressure and protect it. I am not a designer, and It dosent matter where your from those professionals are hard to come by. I don't know your application but I would steer you away from the R-23, high temperatures are the concern, look at R-508B for the low stage. Good luck and keep us posted on your progress.

[mad fridgie]

Your pressure relief valve. You need to consider the amount of mass of refrigerant and the maximum rate of change in conditions. This then gives the maximum flow venting flow rate.
Then you need to then consider the pressure difference across the valve. Marry up the 2 sets of figures to valve manufactures data.
The expansion vessel, again need you need to know your total system mass. Then to what level of expansion you want to choose (Pressure)
Cap sizing, well that is art and with most common data you are still +/- 25%.
I would look at keeping the LT refrig simple as possible and with a constant load.. Look at other methods to control load and conditions. Control evap fans to keep load low at higher rooms temps, trims heaters to keep load high, when actual load is low.

[Louis Joubert]

Thanks for the advice Emmett and mad fridgie.