Barometric Bypass Damper

A question that comes up frequently when quoting zone control systems is, why and when do I need a bypass damper?  As the individual zone dampers close, the system static pressure will tend to rise.  In order to maintain constant airflow through the HVAC system, a barometric damper can be used to bypass some of the discharge air back to the system.  The bypass damper should be installed in such a way as to connect the supply air duct to the return duct.  Damper adjustment is done by moving the weight up and down the arm.  If only two zones are required, size each zone to handle about 75% of the total CFM.  This method does not require a bypass damper.  If one zone requires substantially more CFM than the other, it is recommended that the larger zone damper be set to bleed about 20% of its air.  If more than two zones are required, install a bypass damper.  It should be set to bypass just enough air to maintain a quiet, draft free system.  Barometric bypass dampers can be used on systems with static pressure ratings up to 0.75”W.C.  Bypass dampers are sized based on the cooling tonnage.

Condensing Unit Damper Size
2.5 tons or less 8” bypass
3 tons 10” bypass
4 tons 12” bypass
5 tons 12” bypass
7.5 tons 14” bypass
10 tons 14” bypass

For systems larger than 10 tons, subtract the CFM of the smallest zone from the total system CFM, then size the bypass damper to handle 100% of this difference at 2,500FPM.

Troubleshooting a Z-600 when the compressor keeps cycling off on low limit

Sometimes we get calls from contractors looking for help and information on a Z-600 control board that is cycling off on low limit.  The following are some ideas to keep in mind if you come across this situation.

1) Verify the chip is version 1.6.
2) Verify the low limit adjuster is set at 48°F.
3) Verify the discharge air temperature using an accurate digital thermometer.
4) Is it possible that we are bypassing more air than is necessary and causing the coil temperature to drop?
   a. If we are bypassing too much air we can adjust the bypass damper to open at a higher static   pressure by moving the weight down the arm.
5) Last case measure.  We can disconnect the DAS and not use it.  Use an FS-38 wired in series between Y1 of the board and Y1 of the equipment and install it on the suction line.

There is usually a 20°F temperature difference between the discharge air temperature and the coil temperature; therefore, a 48°F discharge air temperature will give us approximately a 28°F coil temperature.  We do not want to go below 48°F discharge air temperature.

Coils can freeze when there is not enough air going across the coils or if the air going across the coils is to cold.

Possible reasons the air going across the coils is too cold.
1) We are bypassing too much air.
2) Verify the correct setting of the bypass damper.
3) Adjust the bypass damper to open at a higher static pressure by moving the weight down about 1” after you have it set normally.

Possible reasons there is not enough air going across the coils (400cfm per ton)
1) Dirty filter
2) Undersized return air duct
3) Dirty or plugged coils
4) Fan speed is set to low

Join us at our Summer Cookout

Fire up the Grill Summer is Almost Here!

Join us at our summer bash, cookout style on Friday, July 18th @ Jackson Systems from 11 a.m. - 2 p.m.  5418 Elmwood Avenue, Indianapolis, IN 46203

Meet reps from Honeywell, White-Rodgers, and Braeburn.  Free give-a-ways, games, burgers, hot dogs, drinks and more.  Don't miss out!

R.S.V.P. to Erica Gardner at erica.gardner@jacksonsystems.com, 317.222.7208

  Learn more about us at www.jacksonsystems.com

National HVACR Service Managers Forum

Join Jackson Systems at the National HVACR Service Managers Forum October 9 & 10, 2008 at the Doubletree Hotel Houston in Downtown Houston, Texas. 

Service managers are key to contracting success.  Get a leg up on your competition at the Service Managers Forum!

The First Annual National HVACR Service Managers Forum is the first national educational program designed exclusively for Service Managers - the people who run a service department and make a big difference in contracting success.

To learn more about the event, click here.

To register, click here.

to learn more about Jackson Systems, visit www.jacksonsystems.com

111 tips to help your business become more profitable

One of our great industry friends, John Hall, has published a new book about the HVAC industry.  As many of you know John is the Business Editor for The Air Conditioning, Heating & Refrigeration News (www.achrnews.com). His new book is titled Profit Tips 1.1.1. and includes 111 tips to help your business become more profitable. Each tip is endorsed and ‘embellished’ by 111 real-life contractors who have added their names because they believe in them and John thinks you will too.

Here is an excerpt from the book:

TIP #21

     Cheaters never prosper – unless they use cheat sheets. Or should I rephrase that and say – because they use cheat sheets. We all know about cheat sheets. Kids use them in classrooms when taking tests by writing answers down on scraps of paper and hiding them in their shirtsleeve. Or better yet, kids write answers on their wrists or ankles – very clever.
     But not all cheat sheets have to emulate cheating. Some of these little scraps of paper can be called reminder sheets. You have seen them – the yellow sticky notes all over the place with various notes. One of the funniest was from the movie Romancing the Stone where actress Kathleen Turner couldn’t find a tissue to blow her nose so she used the sticky note which said “Buy tissues” to empty her nostrils.
     You may want to put some reminder sheets around your business or in your employee’s weekly paycheck envelope. The message can be inspirational or instructional. Call it a cheat sheet if you’d like – you might be cheating your competition out of a good idea.

     Do we use cheat sheets in our business? That term brings up memories of sitting near the back in Spanish class and observing many students surreptitiously referring to small lists of vocabulary. It is an unpleasant memory because so many were harming themselves, and because they were raising the grading curve. (I assume most of them went into public service, and that is the reason public policy is so bad.) I earned my low Spanish grade honestly, and am proud of it.
     We do use checklists – another form of cheat sheets. We have computer printed checklists for materials and procedures for attic heat pump installations, closet heat pump installations, preventative maintenance, and product features.
     My workers inform me when a truck-stocked item is low, that I write it in a pocket notebook – yet another type of cheat sheet. The result is dramatically reduced incidence of being on the job without a necessary part.
     Our productivity is extremely high, so there is money left for big (inspirational) bonuses on most jobs.

David Green
Green Electric
New Braunfels, Texas

If you enjoyed his last book, the NEXT Contractor, you’ll enjoy Profit Tips 1.1.1. even more. The price is $14.95 plus $3.75 S&H. John is taking orders right now at his website (www.ideaperson.net) -- click on ‘Profit Tips 1.1.1.’ You can order using PayPal and be assured of getting the copies fresh off the press. If you choose to order via check, the address is at the website, too. Order TODAY!

Learn more about Jackson Systems at www.jacksonsystems.com