Appendix A: Component Sketches and Parts List
Laboratory Test Apparatus for Evaluating Devices
that Measure HVAC Supply Grille Flows
Energy Performance of Buildings Group
The test apparatus is essentially a single-branch fan and duct system that LBNL has constructed to evaluate devices that measure airflow out of HVAC grilles, with a focus on determining the sensitivity of measurements to flow non-uniformities. Note that this apparatus cannot determine the effects of insertion losses caused by placing a test device (e.g., a flow capture hood) over a grille of a multi-branch system. Sketches of the test apparatus and its supports, along with a list of the apparatus components that make up the flow path, are provided in Appendix A.
The primary component of the apparatus is the reference flow meter, which is a nominal 6-inch-diameter ThermoBrandt flow nozzle[1] that is mounted between two sheet metal duct sections. The two pressure signals from the flow meters pitot-static array are measured and recorded using one channel of an Energy Conservatory APT auto-zeroing multiple-pressure-transducer data acquisition system that is connected to a computer running Energy Conservatory Teclog software. The rated accuracy of each pressure transducer is the greater of ±1% of the pressure reading or ±2 times resolution for up to 800 Pa (resolution is 0.1 Pa in the 0 to 400 Pa "low" range, and 0.5 Pa in the 400 to 1,000 Pa "high" range), and ±2% of the pressure reading from 800 to 1,000 Pa. The Teclog software averages the pressure data collected during each test. This average pressure and the corresponding average air density entering the flow meter at measurement conditions are subsequently used to calculate the corresponding average airflow through the flow meter.
The rated accuracy of the flow meter is ±0.5% of measured flow over a range of about 100 to 500 scfm. For lower flows, pressure measurement uncertainty causes the flow measurement uncertainty to increase from 0.5% (0.5 scfm) at 100 scfm to about 6% (2 scfm) at 30 scfm. However, even with the increased fractional uncertainty at low flows, the associated low absolute uncertainty means that the reference system is sufficiently accurate for calibrating flow measuring devices that are used in HVAC applications.
A variable-speed axial-flow fan located upstream of the flow meter is used to blow air through the apparatus. The airflow is adjusted manually using a speed control attached to the fan. For safety reasons, a wire guard is located at the fan inlet.
Downstream of the flow meter is a section of flexible duct that connects to a 2 ft. by 2 ft. square grille, which is mounted on a vertical sheet of plywood with the entire grille outlet exposed through an appropriately sized square hole. The downstream edge of the grille sits on an EPDM gasket in a recess cut into the upstream side of the plywood. Clamps on the upstream side of the grille hold the grille against the gasket in the recess. This configuration allows grilles to be easily exchanged in the plywood mount and the mount to be easily moved so that one can study the impacts of grille type and duct inlet geometry on the flow measurements. To make measurements more repeatable, devices being tested are held in place over the grille outlet on the other side of the plywood using four adjustable length bungee cords.
Prior to first use (and after changing a grille), the entire system from the inlet of the flow meter section to the grille outlet is leakage tested. A sealed EPDM-gasketed wood box is fastened to the plywood over the grille outlet and the apparatus is pressurized by injecting air through a small fan and venturi meter attached to the inlet of the flow meter duct section (in place of the larger supply fan that is used during normal operation). The test apparatus component connections are sealed to achieve a total leakage of 0.5 cfm or less at a duct static pressure of 50 Pa (static pressure probe located just downstream of the flow meter). The APT that is connected to the flow meter is also used to measure and record the duct static pressure and the upstream and downstream pressures from the venturi meter during the leakage test. The venturi meter should have a rated accuracy of ±10% of measured flow or better.
To determine the air density for the calculation of airflow through the reference flow meter and to correct airflows at measurement conditions to standard conditions (defined as 21.1ΊC, 101,325 Pa), air temperature and barometric pressure data are collected over the same time period as the flow measurement. An Omega Instruments THX-400-AP shielded thermistor probe (rated accuracy of ±0.1ΊC) and separate data acquisition system are used to measure air temperature at the duct centerline just upstream of the flow nozzle. Barometric pressure is measured using a Nova Lynx 230-355 Handheld Digital Barometer & Altimeter (rated accuracy of ±24 Pa).
Fan Support A
Fan Rigid Duct
Section Support B
Fan Flexible Duct
Section Support C
Flow Meter Rigid Duct
Section Support D
Flow Meter Flexible
Duct Section Support E
Supply Grille Support
F
List of Flow
Components
1.
Fan
KANALFLAKT Inc.
Inline fan, mixed flow impeller, external rotor motor
Type: KD 16
16 diameter inlet and outlet
Rated maximum flow and speed at 0 Pa: 2952 cfm, 1595 rpm (no inlet guard)
Rated maximum static pressure: 470 Pa (1.875 in.w.c.)
2.
Conical sheet
metal transition: 16 to 14 diameter; 4 length
3.
Conical sheet
metal transition: 14 to 12 diameter; 3 length
4.
Conical sheet
metal transition: 12 to 10 diameter; 4 length
5.
Conical sheet
metal transition: 10 to 8 diameter; 7 length
6.
Rigid sheet
metal duct: 8 diameter; 34 length
7.
Conical sheet
metal transition: 8 to 10 diameter; 10 length
8.
Flexible
duct (without insulation): 10 diameter; 6.5 length
9.
Conical sheet
metal transition: 10 to 6 diameter; 4 length
10. Rigid sheet metal duct: 6 diameter; 4
length
11. Reference Flow Meter
THERMOBRANDT Instruments.
NZP1000 Series nozzle/pitot-averaging
air/gas flow sensor
Model: B_NZP1031-6-1
Aluminum flow straightener and nozzle with 316 stainless steel probe array
Rated accuracy: +/-0.5% of measured flow over duct velocity range of 0.89 to 30.5 m/s (175 to 6000 ft/min)
12. Rigid sheet metal duct: 6 diameter; 2 length
13. Conical transition: 6 to 8 diameter; 4 length
14. Conical transition: 8 to 10 diameter; 4
length
15. Flexible duct (8 inside diameter; 6.5
length) with R-4.2 fiberglass insulation on duct exterior. Insulation is used
primarily for maintaining duct shape in studies of aerodynamic effects of duct
radius at supply grille inlet.
16. 2x 2 supply grille.
[1] The term flow nozzle is a bit of a misnomer. The nozzle part of this device is really a flow conditioner. The pressure signals are actually from a pitot-static sensor array mounted in the throat of the nozzle, rather than from the pressures upstream and downstream of the nozzle.