How to Measure HVAC System Airflow

Transcription

1 How to Measure HVAC System Airflow

2 About National Comfort Institute National Comfort Institute is an international training Since our and beginning development in 1994 company we have trained with and Employing our unique practical, experience-based certified nearly 20,000 individuals and served more field approach, we currently work with 9 utility than 5000 companies in 10 countries. Every year companies in 6 states, and partner with other likeminded industry professional we conduct more than day training events organizations headquarters in Cleveland, Ohio. We have offices and training facilities in Nashville, Tennessee, Des Moines, Iowa, and Cypress, California, as well as 9 instructors in regional locations.

3 Air balancing diagnostics reveals massive opportunities for HVAC energy savings that have been hidden from regulators and program managers since duct sealing was first conceived. Up to 40% of a building s heat load can be reduced by renovating the HVAC system

4 Energy Codes are Driving Change

5 Duct Sealing and Duct Leakage Testing Remain the Buzzwords within the Industry Yet Static Pressure and Airflow are Assumed

6 Current Program Results are Failing to Deliver Promised Energy Savings Duct Sealing + High Efficiency Equipment Performance One Reason: Airflow is Still Assumed!

7 Typical U.S. HVAC System Measured Performance (Testing conducted in both heating and cooling modes) 42.7% 57.3% SOURCE: NCI Contractor Surveys to 12-11

8 Typical Performance After NCI System Renovation (Testing conducted in both heating and cooling modes) 6.2% 93.8% 93.8% 36% Less Energy Used SOURCE: NCI Certified Contractor Surveys to 12-11

9 Principles of Measuring System Airflow Airflow has been assumed for decades based on various rules of thumb and design methods Very few installed systems perform as designed

10 As far as comfort and efficiency are concerned, testing and balancing are just as important as the design calculations and the installation protocol. ACCA Manual D - Page 16.1

11 HVAC System Airflow is Measured in Two Places Fan Airflow Delivered Airflow

12 The Principles of Measuring HVAC System Airflow Static Pressure Determining Fan Airflow Air Balancing Hood Airflow Traverse

13 Measuring Static Pressure Static pressure is the resistance to airflow across components and/or through the ductwork High static pressure can reduce the true efficiency of the system, no matter the rating of the equipment

14 How Static Pressure Works in a System The Supply Side of the Fan: Pressure is at lowest highest the discharge on on the supply of the fan side is of the of the total system fan of at all the past discharge the supply pressure of register the drops fan on the supply side of the fan

15 How Static Pressure Works in a System The Diagnostics Return Side of the Fan: Compare the measured total external static pressure to The Pressure pressure is highest lowest at the suction the return side side of the of of fan the is fan the before at total the of the the fan rated pressure all inlet return the of pressure grille the fan drops on the return side of the fan The side of the fan with the highest pressure is usually where the restriction is located

16 Static Pressure Test Instruments A manometer kit is needed to measure static pressure. It contains: Magnehelic gauge or a digital manometer 3/8 drill bit Drill bit sheath for safety Tubes or hoses Hole plugs

17 Static Pressure Test Locations Upflow Gas Furnace High limit switches may be removed and pressure taken at that location. Disconnect power before removing the switch.

18 Static Pressure Test Locations Horizontal Air Furnace Handler

19 Measure Total External Static Pressure T Measure E S P = pressure total of pressure after the taken air exits where the filter air enters and before equipment the air (Suction Pressure enters the -) coil. and where air exits equipment (Discharge Pressure +) Supply Return -.35 Equals.82 -

20 Measure Filter Pressure Drop Pressure drop over an air filter is found by measuring the pressure on each side of a filter and then subtracting the two pressures to find the pressure difference. After Filter.31 - Before Filter -.11 Equals.20

21 Measure Coil Pressure Drop Coil Compare pressure coil drop pressure is also found drop to by the measuring manufacturer s the pressure rated coil on pressure each side drop of a coil, listing and at current then subtracting airflow. If the manufacturer s two pressures rated to budget find the is also pressure.30 at difference. current airflow, this is evidence coil is clean. Before Coil -.41 After Coil -.11 Equals.30

22 Comparing Fan Rating to Measured Pressure Most residential fans are rated to operate at a maximum of.50 of total external static pressure..82 of static pressure on a fan rated at.50 = 200/130 blood pressure in a human

23 Steps to Determining Fan Airflow with Static Pressure 1. Determine the size and capacity of the air moving equipment 2. Inspect the fan and verify it is clean and in good working condition 3. Identify the fan speed setting. Check the fan speed taps, the wiring schematic, or the dip switch settings 4. Using the fan table, plot fan CFM from the fan drive or tonnage, the fan speed and the equipment measured total external static pressure.

24 Identifying Fan Speed Setting Fan Speed Taps Circuit Boards Dip Switch Settings

25 Using Manufacturer s Fan Performance Tables Engineering data courtesy of Lennox Industries

26 Air Balancing Hood Ceiling Diffusers/Grilles Floor Registers Side-wall Registers/Grilles

27 Air Balancing Hood Set the hood to supply or return as appropriate Cover the entire grille/diffuser whenever possible Rock the hood to ensure a positive connection

28 Air Balancing Hood Record supplies first Then record returns Compare actual airflow to a proper load calculation

29 Airflow Traverse Measuring airflow in duct or at the face of a grille or register requires a procedure called an airflow traverse. A traverse uses an anemometer to measure average air speed. When measuring air speed, or velocity in the U.S. the unit of measurement used is Feet Per Minute (FPM). This measurement is converted over to Cubic Feet Per Minute (CFM).

30 Airflow Traverse A duct airflow traverse uses an anemometer to measure air velocity inside the duct. It can be used on rectangular or round ducts.

31 Airflow Traverse Stamped face supply registers: hold the probe perpendicular to airflow on each side of the register and take 12 to 24 velocity readings.

32 Airflow Traverse When measuring airflow through supply registers, a correction factor is required.

33 Airflow Traverse Return grilles: measure by holding the anemometer probe 1 before the air enters the grille. Measure in a grid pattern across the face of the grille, taking a reading every 2-3

34 Finding Hidden HVAC System Airflow Issues Static Pressure Solutions Equipment Airflow Corrections Room Airflow Solutions

35 The Search for the Silver Bullet to HVAC System Performance Many make the mistake of assuming a good design will automatically produce effective improvement results. The rubber meets the road when you actually prove your design was achieved with the results that were intended.

36 Questions?