Balanced port TEVs

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WHERE IS PROFESSOR SPORLAN?????!?!?

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Some thoughts on balanced port TEVs for herefishy :)

With all TEVs, the sensing bulb provides the opening force on the valve, while the superheat spring and equalizer pressures combine to provide the closing force, i.e.:

F_bulb = F_spring + F_equalizer

These are considered the fundamental forces acting on the TEV. More often, TEV operation is described in terms of pressure:

P_bulb = P_spring + P_equalizer

Since bulb and equalizer pressures are easily understood.

When we refer to "force" due to bulb or equalizer pressures, we are taking pressure x the effective area of the TEV diaphragm (pressure x area = force). When we refer to spring "pressure", we are taking spring force and dividing it by the effective area of the TEV diapragm (force / area = pressure).

Using the pressure version of the TEV balance equation, and noting that the spring pressure is effectively constant once the TEV is properly set, we see that the TEV is simply controlling the difference between the bulb and equalizer pressures. This difference in pressure, converted to temperature, is of course the superheat the TEV controls.

So what is this "balanced port" stuff all about? Another force acting on the TEV arises from the actual pressure drop across the valve:

F_port = <font face="Symbol">D</font>P_TEV * Port Area

This force is normally an opening force with the TEV, and one can think of it as the refrigerant flow "pushing" the pin away from the port. Incorporting this force into our equation, we get:

F_bulb + F_port = F_spring + F_equalizer

Interestingly, if pressure drop across the TEV were to remain constant, this force has no real consequence on TEV operation. Spring force will offset it when the TEV is properly set. A problem occurs, however, when this force varies significantly, i.e., the more <font face="Symbol">D</font>P_TEV varies (as head pressure varies from summer to winter operation) and the larger the TEV port area.

As a practical matter, many if not most large capacity TEVs employ some type of balanced port design, and this is due to the fact they have large port areas.

Small capacity balanced port TEV can benefit systems, particularly if head pressure varies substantially from summer to winter operation. In addition, the single rod balanced port design, e.g., Sporlan Type "BF" allows for improved pin port alignment than the conventional two pushrod TEV design. So one can expect better control at low load conditions with the single rod design.

So do this mean we can unnecessarily oversize a balanced port TEV and expect good control? This is not a good conclusion. One should properly size the TEV for the application, whether the valve has a balanced port design or not.

Note that for some low temp applications, the TEV is oversized a bit to provided quicker pulldowns following defrosts. This is a good application of a balanced port TEV as long as one isn't too overzealous with the oversizing. :)

Thank You Prof! I could describe the valve but not nearly so technically nor as eloquently. ;)

I simply use them when I feel it would be of some benefit to any particular application.

Thank you Professor,

Your explanation is crisp and clear in regard to the appropriate application of the "BF" product.

Most often, when I arrive at a new client's site with a refrigeration problem (usually walk-in cooler utilizing up to perhaps 5hp C.U.), I grab my 5/16ths and my flashlight and head straight to the unit cooler to check the TEV before I do anything else. 90% of the time if it is a "BF", when I check pub. #201, the capacity rating of the valve at design SST may be 3 times the system design!

The reason this occurs is because the box which contains the component as it sits on the wholesaler's shelf indicates a capacity of some range, for instance, 1/3 through 1 tons, or whatever (my reference material isn't readily available at this time). "Johnny" assumes that the valve is appropriate for any application within that range.

I have caught a counterman sayin', just grab that "AA", it does it all!

I particularly concentrate on employing balanced port design in multiple evaporator applications. As long as an appropriate selection exists for the application.

:D

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I particularly concentrate on employing balanced port design in multiple evaporator applications. As long as an appropriate selection exists for the application.

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The Type BF valve was developed with multi-evaporator supermarket refrigeration systems in mind. These systems are normally designed to allow head pressure to float, and obtaining quick pulldown following defrosts is becoming more important as product temperatures are being controlled more precisely.

The capacity range stated on a Type BF valve is intended to indicate that the valve can be expected to operate over a wider range of conditions than a conventional TEV, and it should only be used as a guide. Sizing the valve based on capacity range only is no smarter than sizing a conventional TEV based on its nominal rating. It’s far better to verify valve sizing by looking up its rating at the conditions you are operating… Or use manufacturer’s product selection software if you don’t like looking at valve rating tables :)

prof.,

Your response is definitely textbook. I have enjoyed reading your post for some time, and it has made me think further into such a situation pertaining to some application which may be "marginally" within the capacity rating of a "BF" Valve.

Say, that in the course of valve selection that you may be within 5%-10% of any particular selection, what variance should be allowed to the proper capacity of the "BF" in determining the appropriatness of it's application over the variance in the application of , say a "g" model valve?

I.E.... If the design capacity of the system was not a "sure" bet for any eligible valve specs, would the "range" of the BF" valve be taken into consideration to compensate for discrepancy between design capacity, and the black numbers in the "PUB 201"?

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Say, that in the course of valve selection that you may be within 5%-10% of any particular selection, what variance should be allowed to the proper capacity of the "BF" in determining the appropriatness of it's application over the variance in the application of , say a "g" model valve?

I.E.... If the design capacity of the system was not a "sure" bet for any eligible valve specs, would the "range" of the BF" valve be taken into consideration to compensate for discrepancy between design capacity, and the black numbers in the "PUB 201"?

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When rating TEVs, valve manufacturers will generally allow for some reserve capacity. The reason for this is system tolerances and other various "unknowns" can add up to measurably affect valve sizing. If the TEV were rated without a reserve capacity, and it is sized such that system conditions required 100 percent of the valve's rating, then these tolerances and unknowns could cause the valve to be short of capacity. In general, you do not want to rely on the TEV having reserve capacity in your sizing calculations unless you have a very good handle on the necessary refrigerant flowrate requirements and system operating conditions.

If the concern is how much can a TEV be oversized and be expected to function properly, the simple answer is that it depends. Much depends on the evaporator coil design, air flow, and refrigerant distribution. Normally, there is sufficient valve sizes covering a range of capacity such that one only needs to find the smallest capacity valve to do the job. Some applications, such as low temperature display cases that are connected to racks, benefit by have the TEV somewhat oversized, which helps reduce pulldown time following defrosts. So with applications like these, it may be desirable to go with the next larger TEV instead of the smallest which can handle the load.

The Sporlan Type BF series balanced port TEVs do not have as many valve sizes covering its capacity range as do the Sporlan Type F and G series TEVs. The intent here was to use the Type BF valves as a wider range valve on applications where loads and/or head pressures can vary significantly. Perhaps it could be considered for systems that provide more than their fair share of unknowns... :)

I always say, that the day that I don't learn something new in this business, is the day I should quit. Just this week, I have been working on a refrigeration change out and re-spec for a meat warehouse (150,000 BTUH). During the course of all the discussions that I had with manufacturer's engineering departments, the topic arose regarding system capacity rating for TEV sizing.

Normally, I will select the TEV by the capacity of the C.U. at the design high ambient conditions (condensing temperature). A fellow that I was talking to suggested that I should select the TEV according to the capacity of the system under the conditions underwhich it will "normally" be operating in.

Say, Tex. may experience a month of 110degF highs, but the greatest percentage of the year may be 95degF highs. It made me think about my process, however I feel that I've had great success. Furthermore, I began to consider, particularly in the case of the "Q", body valves, my only (infrequent) experience HAS been the under-rating my valve (cartridge) selection.

I think in a way, that the fellow was suggesting basing "system capacity" on degree-days, or some type of averaging scenario. Would that seem appropriate?

Since the subject was brought up, I am particularly interested in the matter, because I am applying extended range C.U.'s at the lower end of the operating range at a 18degF S.S.T., and the capacity curve gets a little steep around those temps/pressures.

Another question for the prof: Since a BF valve and a Q or F valve all use KT43 powerheads, yet the BF valve has only a single pushrod, are these powerheads interchangeable? We have always assumed so, but now I wonder.

Dan

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I think in a way, that the fellow was suggesting basing "system capacity" on degree-days, or some type of averaging scenario. Would that seem appropriate?

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Selecting the TEV based on the highest expected ambient conditions/condensing temperatures is not a good approach. The TEV will have its greatest capacity at these conditions, and this is due to the fact pressure drop across the TEV will be at its greatest. On the other hand, the compressor and the system will have its lowest cooling capacity at these conditions.

Sizing the TEV at the system's "design" conditions is the standard operating procedure, and will normally result in the best TEV selection.

The best way to size the TEV, however, is to determine the <b>minimum</b> condensing pressure where you need the TEV to deliver rated system capacity at these operating conditions. It is at this point where the TEV will have its minimum capacity, and the compressor and the system will have its greatest cooling capacity.

Keep in mind that at low ambient temperatures, it may not be necessary for the TEV to deliver rated system capacity. So one should not unneccessarily oversize the TEV for low ambient/low condensing pressure operation if optimal system operation isn't required at these conditions

Okay,

I'm going to go through my valve selection process for this job on this post. Now, I won't be goofing off at my computer, because this will be the basis for the (tentative) valve selection for the job.

I have (3) Bohn BHE 450 Unit Coolers, electric defrost, Design S.S.T 18degF at 10degF T.D. for 28degF room.

scenario 1 - (1) Bohn BLV2501H6 C.U. R-404A
@ 110degF ambient / 20degF S.S.T. = 157,570 btuh
@ 100degF = 174,260
@ 95degF = 182,610
Since my S.S.T. is slightly lower than the 20degF rating, and the next rating in my book is 15degF 141,860 buth @110degF, I will kinda' split the difference and call it 151,200 @110degF

Each evap @ approx 50,400 btuh or 4.2 tons

Now, because of the multiple evaporator situation, my first thought is a valve of balanced port design, but geez... the 201 jumps from a "C" @3.0 tons to a "6" @ 5.63 tons. That doesn't suit me well.

I sure like the initial figure in the "201" for the C or S "4" which shows 4.28 tons in the chart. If I adjust for liquid temperature (90degF), and pressure drop (175 psi), it approaches a rating of
5.6 tons. I don't know.... seems kinda' fat to me.

the H "4" figures out with PD and liquid temp. at about 5.02 tons.... maybe a better selection, and seems to mach the capacity of my C.U. @ about a 95 degF ambient (normally I wouldn't have considered the capacity at 95degf). I think I'd go with the H "4". The valve body design I consider appropriate for the application, also.

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Since a BF valve and a Q or F valve all use KT43 powerheads, yet the BF valve has only a single pushrod, are these powerheads interchangeable?

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Absolutely! (E)BF, SBF, (E)F, (E)Q, SQ all use the #43 element and can be interchanged. The #43 element is also used on the Sporlan Type BI valve, which is used on Hussmann impact cases. The only problem with changing elements with this valve is the majority of BI valves are ordered nonadjustable, and changing the element will likely affect valve setting with any of the valve types. With the aforementioned valves, you can compensate for any change in setting using the valve adjustment.

Changing some larger capacity Sporlan TEVs may require a superheat spring change to get optimal adjustment.

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I'm going to go through my valve selection process for this job on this post.

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The Prof will cheat a little and use product selection software he as developed for this purpose... :) One may download a zip file containing this program from here. Unzip the files to a temporary subdirectory and run the 'setup.exe' to install. After installation the unzipped files can be deleted.

No question the EBFSE-C-C would be a bit small for the coil capacity, particularly when one accounts for distributor pressure drop. The next larger balanced port valve is the EBSSE-6-C, which would be ok to use, but the SSE-4-C, a conventional TEV, is a closer fit.

If you are inclined not to allow head pressures to fall much below 95°F, the Prof would use the SSE-4-C. If you wish to run head pressures much lower, say down to 70°F, you would likely be better off with the EBSSE-6-C. "What if" scenarios such as these can be easily handled with the product selection software

I do like to keep my "head" up there a bit.

What kind of control can expect out of the Bohn "Limitizer" control that will be employed in my C.U. selection? In disvussion with Bohn, I beleive that the REp referred to it as and adjustable 2-valve configuration of a head pressure control. OROIA?

I have at times downloaded a "winzip" program, shareware thingy, particularly in conjunction with a Texas gov'mt website that pollutes my confuser. Is there a good source for such a program or can I get it off the shelf?

I do have a sporlan valve selection program, do you suppose it is the same program that you are referencing (v2.99)?...... I like the control of using the tables.

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Bohn, I beleive that the REp referred to it as and adjustable 2-valve head pressure control OROIA?

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More likely an ORI/ORD combination. If so, it will allow you to set minimum head pressure where you wish.

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I do have a sporlan valve selection program, do you suppose it is the same program that you are referencing (v2.99)?

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Current version is 3.07a. The 2.99 version is actually quite old. You should find v3.07a much easier to use. there is no problem running both versions on your PC if you wish.

So if I was inclined to set minimum head pressure according to TEV characteristics, do you consider the H 4 to be in the range of the "best" selection?

:rolleyes: Oh, I misread... you recommended the "S" 4.....

disregard this post.... I'm thinking.

Where do you suppose that the discrepancy in my selection lies? :rolleyes:

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Where do you suppose that the discrepancy in my selection lies?

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Mmmmmm.... the Prof wiill need to see your math.... :)

Well, I took the TEV rating indicated in the table of the "201" (404A @ 20degF S.S.T.), multiplied that rating by the liquid temperature factor at 90degF (1.11), and then multiplied that result by the PD factor at 175 PD (1.18) for the final result.

Then I rationalized the information per above post. Maybe rationalization was the discrepancy? :D

I have been negligent in the past of adjusting capacity ratings in the tables for liq. and PD (according to the factor tables under the TEV rating table ... ref. p.6). As such, typically I would see the 4.28 rating in the table (in this case) for the 4.2 ton application, and make that selection. However haphazard that it might be, it has worked in the past, and justifiably so according to this example and your recommendation.

I have spot checked myself with mfgr reps and engineering depts. (including Sporlan... perhaps I've talked to you) and I cannot recall my selection ever having been poo-pooed by anyone when I merely base the selection on the TEV rating in the rating table.

.... But now that I've had some time to think about it... It appears that what I DID (in the above example) was to calculate the capacity of the valve under the expected system conditions under which it (TEV) would have it's greatest capacity. Reading further into some "Sporlan" literature and and considering what you and others have told me, I now understand that valve selection should be based on the MINIMUM expected valve capacity.

The primary error in my math (whether or not it was mathematically correct), was that I based the PD across the valve at the highest (capacity) that the valve is anticipated to experience.:)

It seems that the Rating Tables for valve selection are calculated for "typical" expected minimum valve capacities. As such, the Table "default" appears to be applicable to my region of the planet on a consistent basis, pertaining to the applications that I typically employ.

If I am right, I did not know that was what I was (in effect) doing.:p

I beleive that the two or three applications that I did undersize a valve, that I actually adjusted the table rating for the HIGHEST expected TEV capacity (matching to least expected C.U. capacity), and as such the results!

Minimum valve capacity occurs at maximum C.U. capacity..... Maximum valve capacity occurs at minimum C.U. capacity. Of course the system balances due to the change in S.S.T., and the resulting NRE of the unit cooler. Is it simply necessary to assure that at minimum valve capacity, there's enough there to do the job?

I can now visualize the system "See-Saw".

Firdge...

For the sake of argument, assume that all is taken into consideration in regard to the PD (which normally I do take the aforementioned by yourself, into consideration). Because the conclusions that I have drawn in this example are WAY OUT OF THE BALLPARK (by my standards) for any properly engineered system!!!!

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Is it simply necessary to assure that at minimum valve capacity, there's enough there to do the job?

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Minimum TEV capacity should occur at minimum operating head pressure for the system at design evaporating temperature, where the compressor will have its greatest capacity. If the TEV has sufficient capacity at this operating condition, it will cover your capacity needs at the higher operating head pressures.

Sizing the TEV at "design" operating conditions is still standard operating procedure. But if system head pressures are going to fall off considerably from design conditions, then TEV sizing at these conditions should be verified. It may well be necessary to increase the size of the TEV to obtain proper low head pressure operation.

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If the TEV has sufficient capacity at this (low head pressure) operating condition, it will cover your capacity needs at higher operating head pressures.

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So the statement, "Valve selection should be made according to 'normal' operating conditions", is not exactly correct.

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So the statement, "Valve selection should be made according to 'normal' operating conditions", is not exactly correct.

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Like with most things, there are exceptions to the rule. But if every technician and engineer sizing TEVs were to follow the above statement, there would be far less improperly sized TEVs operating on systems. :)