charging question

[hvaccop]

When charging a walk in cooler in the winter time with a headmaster with say R-22 once you have cleared the sight glass how much more charge do you need to add or would you basically charge it superheat

[cyro]

Depends on your ambient temp

[jaybee]

Depends on your ambient temp

Please explain.

[hvaccop]

I have always been told when charging a ref. system with a headmaster in the summer time, say 80 degree ambient, clear the sight glass and put about half the receiver capacity. Never had a clear explanation how much to add just heard this rule of thumb

[the mojo]

Headmaster charging: Calculate if the receiver is large enough to hold the whole charge, just don't guess at it and say half the receiver's capacity. The formula is : V = 3.14 x R 2 x L or H x 45 x .80 80% capacity on a 90* day. 45 represents refrigerant weight per cubic ft. Know the density of the gas you are using by using an ASHRAE guide. Then there is the calculation of condenser capacity tubing used (diameter) and the length of tubing. The short hand method is 2.5 lbs. per system ton. Charge to a clear glass and then weigh in the extra refrigerant for condenser flooding. Then double check your work. Front seat the King valve. Use will see the head rise 10-15 psig then fall. Next check your pump down. Kill t-stat power to LL solenoid and observe the head capacity. :cool: breeze

[icemeister]

When charging a walk in cooler in the winter time with a headmaster with say R-22 once you have cleared the sight glass how much more charge do you need to add or would you basically charge it superheat

Sporlan has a good explanation of how to do this by calculation:

http://www.sporlan.com/90-30-1.pdf

Generally, when the ambient is above 70ºF the head pressure will be above the 180# setting of the Headmaster and the condenser will be 0% flooded. To determine how much additional refrigerant is required to flood the condenser for low ambient operation you first need to establish what your minimum expected ambient will be. Then you need to calculate the amount of refrigerant needed to flood the condenser 100% using the chart in Table 1.

Using the chart in Table 2 with your suction temperature and minimum ambient you can determine the percentage of the condenser flooding required at your minimum ambient. Multiply the 100% amount you calculated by the percentage required at the minimum ambient and that's how much you need to add.

Now if you're charging a system when the ambient is below 70ºF, charge the system to just clear the sightglass and look up the percentage requirement at the current ambient temperature. Subtract that from the minimum ambient percentage requirement and that is the how much you need to add to complete the charge.

This method appears somewhat daunting at first, but once you've done the calculations a couple of times it's not so bad. With the measuring tube lengths, counting the number of tubes and doing the math it takes maybe 1/2 hour give or take.

One word of caution here however. You should never charge a system with pumpdown control so the receiver is more than 80% full when pumped down at higher ambients. Don't always assume that your receiver is adequately sized to hold both the normal pumpdown charge and the condenser's low ambient flooding charge. To do that, you'll have to do some more cyphering. ;)

You can estimate the normal pumpdown charge by adding up the evaporator's normal operating charge (from manufacturer's data), the amount of refrigerant liquid in the liquid line after the liquid line solenoid valve and the amount vapor in the suction line back to the compressor. Then you need to look up the capacity of the receiver you have. There's a good section this here:

http://www.suva.dupont.ca/pdf/RefrigPipingHandbook.pdf

Figure on about 10% of the receiver capacity is needed for a operating liquid seal and add to that your calculated pumpdown and the condenser flooding charges. If your less than 80% of the receiver capacity, you're good to go.

[hvacr man]

use the icemeisters way it works.

[Airmechanical]

The formula is : V = 3.14 x R 2 x L or H x 45 x .80


hold on, i am gonna call Albert for this one! :eek:

Mr. Albert Einstein :D



.

[hvaccop]

Appreciate Icemeister, seems alittle intimidating but I will give it a shot. I had some trouble with a minature grocery store/meat martket I did last year getting the charge right. Let me tell you how screwed up this deal was. I had several walk in freezers and coolers, several reach in meat cases, produce cases, and dairy cases. One great big coffin freezer. I refrigerated all this with condensing units instead of rack system. The big kicker is the owner bought most of the equipment used from a ref. wholesaler and I had to match up what i could and get a few new pieces to finish the deal. You talking about a pain in the butt.

[Andy Schoen]

Appreciate Icemeister, seems alittle intimidating but I will give it a shot.
icemeister's diatribe on this subject is better than I could give. Perhaps we might collaborate on a version of 90-30-1 that will be easier to use. ;)

[mccool]

Good then, formula exists, is never used. Typically recheck system in low ambient condition and charge if required. Thats the way it works in the real world. Works and is billable everytime no explanations and/or formulas required. :D

[icemeister]

icemeister's diatribe on this subject is better than I could give. Perhaps we might collaborate on a version of 90-30-1 that will be easier to use. ;)

Thanks Andy, but I think what you have there is fine. The only problem I see with 90-30-1 is the omission of the receiver capacity thing.

[icemeister]

Good then, formula exists, is never used. Typically recheck system in low ambient condition and charge if required. Thats the way it works in the real world. Works and is billable everytime no explanations and/or formulas required. :D

I have to agree with you on this. The real world of flooded condenser control doesn't see a lot of refer techs crunching numbers to check their charge. I don't do it very often myself.

I think the better way to look at this however is if we in the field have a better understanding of how (and why) these control work in a system, then we will have a better chance of recognizing a problem and knowing how to correct it.....which is essentially what our job is all about.

If we fail to utilize the resources available to us to solve problems then we are not doing our job.

[the mojo]

I'll let you in on a little secret..... In the real world of T&M you don't have the time to calculate receiver capacity. There is the long way for it, and there is the short of it. I'm sure you get my drift. ;) To the new techs and to other techs who possibly been taught too many "short cuts" its there for the taking. The formula just popped into my head.:D Been using the 2.5 rule for a long time.

[yotaman16]

Is the "flooded condenser control" a head master?

[the mojo]

Yes it is.

[yotaman16]

Headmaster charging: Calculate if the receiver is large enough to hold the whole charge, just don't guess at it and say half the receiver's capacity. The formula is : V = 3.14 x R 2 x L or H x 45 x .80 80% capacity on a 90* day. 45 represents refrigerant weight per cubic ft. Know the density of the gas you are using by using an ASHRAE guide. Then there is the calculation of condenser capacity tubing used (diameter) and the length of tubing. The short hand method is 2.5 lbs. per system ton. Charge to a clear glass and then weigh in the extra refrigerant for condenser flooding. Then double check your work. Front seat the King valve. Use will see the head rise 10-15 psig then fall. Next check your pump down. Kill t-stat power to LL solenoid and observe the head capacity. :cool: breeze


So your saying the short way to charge a headmaster system in the summer or abover 70 degrees is to clear the sightglass and then add 2.5 lbs of gas per ton?

[the mojo]

So your saying the short way to charge a headmaster system in the summer or abover 70 degrees is to clear the sightglass and then add 2.5 lbs of gas per ton?

Yes,but remember don't forget the long term to calculate a system charge. Just not only for service work every day but also for repair quotes and new system installs. And that reminds me you must also calculate the u-bends in your condenser.

[yotaman16]

Thats good to know.. Why are some systems with headmasters diffrent tho. I worked on a freezer unit that wanted you to block the condenser off to get 225 psi head (R 502) and then clear the glass from there and that was the correct charge. Why is that?

[acoolguy]

The Mojo's Formula
"V = 3.14 x R 2 x L or H x 45 x .80 80% capacity on a 90* day. 45 represents refrigerant weight per cubic ft."
indicates that the density or R-22 is 45 LBS per Cuft.
The Icemeister's Dupont PDF says it's about 75 lbs/cuft.
Can Anyone please explain??