Bonus Room (FROG) Installations - Comfort …

1 zoning TIPS from Bonus room ( frog ) Installations Rev. 8-1-08. A Bonus room , or frog (finished room over the garage), is one of the hottest (no pun intended). applications for zoning . zoning allows the consumer to control the temperature in the Bonus room with a zone thermostat, while using only one central heating and cooling system. Without a thermostat, a Bonus room will be TOO HOT summer and winter and consumers will be unhappy. Codes in some states, such North Carolina, include ACCA Manuals J and D as part of the design criteria. Manual D plainly states on page 1-1 that, 2 F is ideal, but 4 F is the maximum allowable difference is equal to 4 F . 8 to 12 degrees differential is common in Bonus rooms without a thermostat. Frequently asked questions about Bonus room applications How do I size the HVAC unit?

2 The total loads for the Bonus room plus the rest of the house controlled by the same HVAC system are combined. Can I undersize the HVAC unit significantly? No. Years ago, at least one prominent manufacturer claimed that, with zoning , a house with a 4-ton load, for example, could use a 2 to 3-ton unit. Only under extremely rare circumstances, did this equipment sizing method work satisfactorily. zoning usually got the blame when the system didn't do the job. The problem was not zoning , it was the design. If only one small zone is calling, will it harm the HVAC unit? No, as long as a properly sized bypass damper and capacity control is included in the system. What is a bypass damper and how does it work? A bypass damper must be installed between the supply and return ducts.

3 The bypass damper will automatically open and bypass air normally delivered to the closed zone(s) directly from the supply to the return. For example, a typical Bonus room application might have a 3-ton unit with one 16 zone for the main house and one 12 zone for the Bonus room . If the Bonus room is designed for 450 CFM, the remaining 950 CFM (1200 450) will bypass directly to the return, thus maintaining a nominal 1200 CFM across the coil or heat exchanger. For a comparison between barometric and electronic bypass, see Bypass Damper TIPS. How do I size a bypass damper? A bypass damper is sized according to the worst case scenario only the smallest zone calling. Assuming 400 CFM per ton, subtract the CFM of the smallest zone from the total CFM.

4 What's left is the Bypass CFM . Never undersize the bypass damper. Increasing to the next size is not a problem for borderline conditions. Bypass Damper Maximum Bypass Size CFM. 8 600. 10 800. 12 1200. 14 1600. 16 2000. What is capacity control and how does it work? The first rule of zoning is to never install zoning without a capacity control. Capacity control protects the compressor or heat exchanger from extreme temperatures during bypass by relaying the supply air (leaving air) temperature to the controller. For example, on a typical summer day, the leaving supply air temperature might be 58 F with a 76 F return air temperature. When the bypass damper opens due to one or more zones not calling, this 58 F supply air bypasses to the return and mixes with the 76 F return air.

5 Over time, the supply air temperature drops simply because the average return air temperature is falling. Cooler air in = cooler air out. Capacity control monitors the leaving air temperature with the leaving air sensor and cycles the compressor off for 3 minutes if the temperature drops below the adjustable 41-48 F cool cutout, thus preventing the indoor coil from freezing. The heat pump high limit is 120 - 125 F and the limit for gas furnaces is 135-150 F. Bonus room installation Tips (page 2). Page 1 0f 2. Bonus room installation Tips 1. Size the Bonus room to add extra CFM capacity. 25-35% is recommended. The thermostat will satisfy a little quicker on extremely hot days. This will allow the compressor to run without interruption from the capacity control.

6 2. Oversize the diffusers in order to reduce air noise. Even with a bypass, a comparatively small zone typically will sometimes deliver more than the design CFM making a little more air noise than normal. 3. Allowing a small amount of air to leak through the largest zone may reduce noise in a small Bonus room zone and also allow longer run times in the small zone in order to satisfy at the thermostat rather than cycling off the compressor with the leaving air sensor. All POC zone dampers are equipped with a minimum stop feature for this purpose. See CSi Product Bulletin Minimum-Stop Zone Dampers dated 6-9-05 for complete details. 4. Always add a balancing damper at the takeoff in small zones. The balancing damper can be attached directly to either side of the zone damper.

7 Just make sure the shafts of the zone damper and the balancing damper are perpendicular to one another (like the crosshairs in a rifle scope). Any excessive air noise can adjusted with the balancing damper. A POC damper features a max open adjustment which may take the place of the separate balancing damper. 5. Thermostat location is critical. In some Bonus rooms all the walls are exposed to the attic. Warm wall surfaces behind a thermostat can cause the thermostat to display inaccurate room temperature. Always install the thermostat on an interior wall if one is available. Completely seal the hole where the thermostat wires penetrate the wall. Add an insulated thermostat back plate (such as Simple Comfort 's ACC-WP01 or WP02). Do not locate digital thermostats next to a return air grille.

8 Also, be sure thermostat is not directly in the path of supply air. 6. Install an adequately sized return air duct in the Bonus room even if there is not door at the Bonus room entrance. 7. If the Bonus room is used infrequently, it is a good idea to add an optional damper to the return duct as well. This will prevent extreme temperatures from entering the return air plenum. Ask for a copy of zoning TIP Infrequently or Seasonally Used Zones for further information For more information about zoning , call the #1 zoning distributor in the Carolinas! 115-9 Hinton Avenue, Wilmington, NC 28403 phone 910-452-0740 fax 910-395-8271. WE MAKE zoning SIMPLE! Page 2 of 2.