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Case Study: HVAC Blower Performance with Multi-Stage, Variable Speed Equipment and Zoning

HVAC Zoning and multi-stage, variable-speed equipment seem to be a match made in heaven by the airflow gods. But how great is it really? We decided to investigate a recent installation by one of our contractor customers.

The application was a two-story, 1,900-square-foot home that several family members continuously occupied throughout the day. It was an older home that initially had no ductwork running to the 2nd floor, just one 12X12 grill in the floor to allow heat to migrate upstairs. The contractor did install a supply duct that feeds five 2nd floor ceiling registers from the attic.  The 2nd floor does not have any return air ductwork. Before the zoning system, the homeowners reported experiencing comfort issues if the bedroom doors are closed tightly all night.

The homes’ existing equipment included:

  • Two-stage, 90%, 70,000BTU furnace with variable speed blower
  • Single stage, 10 SEER, 2 Ton (R-22) air conditioner

The contractor installed:

  • HeatPumPro® 3 Zone Control Panel by Arzel®
  • Three single-stage thermostats

To address the customer’s usage patterns and comfort needs, the contractor divided the house into the following zones:

Zone One – 1st Floor – Main living area, 575 square feet

Zone Two – 1st Floor – Kitchen and dining area, 500 square feet

Zone Three – 2nd Floor – Bedrooms, 825 square feet

After operating for 30 days in the home, we were able to analyze the system’s blower operation by using data loggers, monitoring the blower, heat mode and cooling mode cycling produced some interesting findings.

Blower Usage

The HeatPumPro® has a capability called zone weighting which allows a contractor to control fan speed based on the amount of ductwork that is being served. In this case, the air handler threshold was set at 70%, which initiated W2 furnace operation or Y2 blower operation only when Zone Three is being served with either Zone One or Zone Two. (Example: Z1 40% + Z2 30%=70%). If any of the zones are calling by themselves, the air handler stage threshold will not be met and the second stage call will not run.

By controlling staging on capacity/demand requirements, this eliminates the need to bypass the excess static pressure that would otherwise be caused by the equipment delivering 2 stages of heating to a zone that is not large enough to accommodate that airflow without air noise issues occurring. We eliminate bypass, eliminate LAT issues, and achieve maximum dehumidification by satisfying zones on a low stage or low blower speed.

We sometimes tend to ignore the fact that low-stage operation, when serving a majority of the ducts, will create this same “oversized supply outlets” scenario and cause ineffective BTU delivery. The Arzel® HeatPumPro® panel uses the field “adjustable Zone Weights” and an “Air handler Stage Threshold %” to provide the proper management of CFM volume.

THE BOTTOM LINE – 20% reduced runtime

Because of the use of HVAC zoning, the system runtime was reduced by 20% during the day while still helping to adjust the air supply to the upstairs bedroom.

Additionally – While the Arzel® Zoning systems was only operating on Y1 or W1, the dynamics of the zoning system showed we were delivering more BTU’s and CFM’s, with more Velocity and Throw at the register face to the calling zone, maximizing the effectiveness of HVAC zoning and reducing system run-time by putting all of the conditioned air, where you want it, when you need!

Are you interested in learning more about the HeatPumPro® zoning panel? Schedule a free virtual training on one-on-one basis on your schedule and find out how the HeatPumPro® can help you set yourself apart by offering reliable pneumatic HVAC Zoning solutions to your customers.

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HVAC Zoning and multi-stage, variable-speed equipment seem to be a match made in heaven by the airflow gods. But how great is it really? We decided to investigate a recent installation by one of our contractor customers. The application was a two-story, 1,900-square-foot home that several family members continuously occupied throughout the day. It was […]

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