TXV tonnage question.

[wannafreeze]

Tecumseh comressor mn. caj4492y
I need to select a txv for this cap tube system conversion. I was told by the manufacturer of the case (royal pd06lscb) that I need a 1/2 ton txv.My supplyhouse engineer says the same.Is there a rule of thumb to go down in size when its in between?

[luvcldair]

Most Txv's feed plus or minus 50% of rated tonnage

[k-fridge]

TXv's should be sized to the evaporator coil, not the compressor. BUT,,,since you're replacing a cap tube you may not have any numbers to work with. Under the circumstances I would use a 1/2 ton valve and I think you'll be fine. Just check your superheat afterward and make any neccesary adjustments to get it within parameters.

[rocket]

so a 12,000 btuh coil used with a 24,000 Unit should
have a 1 ton TXV. thaT JUST DOESN'T CUT IT

this situation is that the 12,000 btuh coil will handle
24,000 btuh of the unit at 20 deg TD, which would be
normal for a meat prep room. so this coil, which has to
handle 24,000 btuh at 20 deg TD needs a 2 ton TVX

always rating coils a 1 deg TD will lead to better sizing
of TXV and also the dismissal of the myth that coils produce btuh

NOW, TO ANSWER YOUR QUESTION
when in between sizes
sporlan with tell you to go down
alco will tell you to go down
I will tell you to go down
many on this board, like "size to coil" guy, will tell you
to go up, the next bigger size. Just contact your local
sporlan and/or alco rep and ask.

[k-fridge]

many on this board, like "size to coil" guy, will tell you
to go up, the next bigger size.

Actually I advised him to go down. The compressor is a 3/4 ton and I advised a 1/2 ton valve.

And I respectfully disagree with your comments regarding sizing.

[rocket]

depending on coil usage, the desired TD will vary
shouldn't the TXV be sized to the load ?

desired TD coil rated at 12,000 btuh coil is
5 to 7 TD flowers @7 TD 8,400 btuh 3/4 ton TXV
cooler 10 TD @10 TD 12,000 btuh 1 ton tvx
wine 15 TD @15 TD 18,000 btuh 1-1/2 ton txv
meat prep 20 TD @20 TD 24,000 btuh 2 ton tvx

or do we size all TXV at 12,000 btuh 1 on
(after all, it is a 12,000 btuh coil)

[k-fridge]

Originally posted by rocket
depending on coil usage, the desired TD will vary
shouldn't the TXV be sized to the load ?

desired TD coil rated at 12,000 btuh coil is
5 to 7 TD flowers @7 TD 8,400 btuh 3/4 ton TXV
cooler 10 TD @10 TD 12,000 btuh 1 ton tvx
wine 15 TD @15 TD 18,000 btuh 1-1/2 ton txv
meat prep 20 TD @20 TD 24,000 btuh 2 ton tvx

or do we size all TXV at 12,000 btuh 1 on
(after all, it is a 12,000 btuh coil)
Maybe we're spliting hairs here, but you're still sizing by the evaprator size, not the compressor size. Sure you're factoring in the TD, but you're still sizing by the evap BTU at that TD. Also most TXV's have enough range to cover all but possibly the 20 degree TD.

What if you get into a multiple evap set up or a mismatch and try to size by the compressor? Yeah, trouble!

[rocket]

nobody but you said "size by the compressor"
size by the load is what was stated

what load a given evaporater should handle
is part of the sizing process

Again you do not size by the evaporator, but you
size TXV for the load the evaporator will handle

that 24000 btuh evap at 10 TD may be sized for
12000 btuh at 5 TD or 48000 btuh at 20 TD. its your
job to know which.

the compressor is an important part of that load
in fact it is the only part that produces btuh.

which portion of the compessor btuh will be handled
by which of the multiple evaporators is your job to
know and to size for.

the relationship between the compressor and the
evaporator is the TD

Good idea to check out page 16 of HeatCraft Engr manual
(actually good idea to check out complete manual)
here's link to download
http://www.heatcraftrpd.com/resources/wiringdiagrams/H-ENG-2.pdf

[k-fridge]

Tke your arguement pills today Rocket?? http://www.easysmileys.com/img/smile_color.gif

You kinda fired the first shot when you misquoted me about sizing up the valve and now you're taking the discussion way beyond where it needed to be for the OP who is not yet ready for that much info.

So I'll let you finish without me.http://www.easysmileys.com/img/smile_biggrin.gif

BTW, I occasionally do field consulting for the company whos link you posted.

[rocket]

wannafreeze
my guess is that this appears to be a MT R12 system
1/2 ton TXV probably OK, no problem there
you should size and add a receiver as well

but main point is why are you converting this
to TXV, what problems are you having. If you
are converting to solve a problem, chances
are that conversion may be the wrong answer.

[wannafreeze]

Originally posted by rocket
wannafreeze
my guess is that this appears to be a MT R12 system
1/2 ton TXV probably OK, no problem there
you should size and add a receiver as well

but main point is why are you converting this
to TXV, what problems are you having. If you
are converting to solve a problem, chances
are that conversion may be the wrong answer.

Well this guy has 4 fridges he wants to put their condensors in the basement.They are all pretty new and he was told by the tech. support when he bought them that he could get them remoted easyly if he wanted.I talked to the same tech.sup.guy and was told I have to buy new condensors,txv,solenoid valve,LPC etc.On my previous post I talked about this job that I may do.I am gonna check that heatcraft manual.Sizing units, btu calculations in refrigeration,evap selections and details have been my weakest areas, I need to educate myself so badly on these issues.At shool they didn`t talk about them and no boss let me in on these issues now that I am on my own I am forced to learn all these.

[rocket]

good, the Heatcraft manual will be helpful

be careful on remoting units to basement, make sure
you have adequate makeup air or you will wind up
recirculating air. if you don't have make up air,
it will not work. Romting units is fine, remoting
units to closde space as a basement is DISASTER.

check around your area for someone that can help
(sub-contract) you, as what your customer is asking
may not be feasible. Don't get stuck !!!!!

[icemeister]

Rocket's advice about proper ventilation is correct. That heat that's generated has to have some place to go. If the basement area is underground, sizable and the amount of refrigeration is relatively small (like around 1000 sf/hp) and you're in the north with low ground temperatures you may need no additional ventilation at all. To be safe though, it's best to provide positive ventillation....exhaust and makeup.

To figure how much air you need, you'll need to know how much heat will being generated by the condensing units. Start by gathering the performance data on your equipment from manufacturer's info. For the Tecumseh compressor you listed, the AJ4492Y, pick the Tecumseh unit with that compressor on it......AJA4492YXDXC using Tecumseh's site:
http://www.tcc-nacg.com/

Do a detailed search on that unit, pull up the performance data and go to the conditions you expect to run at.....say +20ºF evap and 90ºF ambient and you'll find that it'll do 5120 btu/hr and draws 940 watts at that condition. To calculate the total heat of rejection (THR) convert the power in watts to btu/hr by multiplying by 3.412 and add this to the cooling capacity:

THR = 5120 + (3.412 x 940) = 8325 btu/hr

The amount of air for ventilation is typically based on a 10ºF temperature rise so using the formula for sensible cooling:

( Q = 1.08 x CFM x TD), the CFM required would be:

CFM = Q / (1.08 x TD) or 8325 btu/hr / ( 1.08 x 10ºF) = 770.8 CFM.

There's an old-timer's rule-of-thumb of 1000 CFM per HP that is fairy common as well. This is where it came from. ;)

[rocket]

icemeister
thanks for the CFM data
very helpful to "wanafreeze" and for me
as always, you are a wealth of knowledge

[icemeister]

It's nearly the only wealth I have left to share. :D

Another suggestion. In deciding on placement of the units in the basement, place them in the makeup airflow for best cooling. The exhaust can go anywhere and control can be a simple close on rise t'stat set at 90-95ºF.

In the old days, we used to construct an plenum at the intake and set the condensers at openings in the plenum so they draw raw OA and blow into the space. If you want to get fancy, add thermostatically controlled modulating dampers to close on temperature drop on the intake tied to a second set on the plenum for recirculation from the basement room. No low ambient controls on the units needed.

There's another rule-of-thumb for compressor rooms with water-cooled or remote air cooled systems. It's 100 CFM/HP. It's based on an assumption that about 10% of the THR is rejected directly by the compressors and associated components and piping in the motor room.

[wannafreeze]

Thanks for all the good info.I am printing these.

[rocket]

wannafreeze, you appear interested in learning so heres some info you won't find in books or schools. Combine this with the valuable info icemeister presented and you will do well.

In the early days of refrigeration, evaporator coils were all rated at 1 deg TD.
A 1000 btuh coil at 1 deg TD was rated at
1 TD 1000 btuh
5 TD 5000 btuh
10 TD 10000 btuh
15 TD 15000 btuh
what this really meant is that the coil could handle various unit btuhs within the proper design TD. In air cond we called it an air handler. In refrigeration there are various TD's used based on product types and application. Good idea to check out page 16 of HeatCraft Engr manual for suggested design TD's.
(actually good idea to check out complete manual)
here's link to download
http://www.heatcraftrpd.com/resources/wiringdiagrams/H-ENG-2.pd

then in the early 60's coils began using 10 deg TD as the
standard rating point. 12000 btuh at 10 TD began to be called a 12000 btuh coil. This did not end the fact that various TD's are used, now the confusion of the 12000 btuh coil came into play.
(larger coils still rated at 1 deg TD to avoid this confusion)

"I've got a 24,000 btuh" coil may actually be false, in a meat prep room this 24,000 at 10 TD coil will normally handle 48,000 btuh at 20 deg TD. i.e. 4 ton coil with 4 ton txv.

The point is if you don't know the coil design criteria you won't know how to size TXV. The coil does not produce btuh, it handles btuh. Sizing a TXV to the coil size is difficult if you don't know the btuh it is going to handle. In example above, a 12,000 btuh coil can be sized for:
7,200 btuh at 6 TD
10,000 btuh at 12 TD
12,000 btuh at 10 TD
18,000 btuh at 15 TD
24,000 btuh at 20 TD

So to size the TXV only for the published 10 TD rating can be foolish. Those that say size to evaporator coil may not know this, they assume coil size is it's published rating (10 TD). As you can see above, The coil may handle varying btuh loads, that is what you need to find out to size
TXV. What btuh load will this coil handle ? I serviced a lot of meat prep rooms, most had wrong TXV as they were sized by published 10 TD coil rating.
Luckily most display coolers are sized at 10 TD to 12 TD so thinking published 10 TD rating is what to size by may be OK (accidently OK). With meat prep rooms,
wine boxes, flower boxes this will get you in trouble.

Now here is a little secret trick for you. Size a box and select a Cond unit. Take selected Cond unit capacity and divide by desired TD (from page 16 Heatcraft manual)
ex: unit is 18,000 btuh for your 40 deg wine box, wine is at 15 TD. 18000 / 15 = 1200
(this is the coil rating at 1 deg TD)
now go to coil rating section of catalog and see the 10 TD ratings column, drop the last zero to make it 1 deg TD, then you will have a direct match. this example will pick a 12000 btuh at 10 TD coil, but it real is a 18000 btuh coil at 15 TD. WOW a direct match. Keep this secret, as it has been kept secret from many techs for years. it will give you a competitive advantage.

Study and learn, but learn it right.