SOP 11. Ventilation Fan Monitoring

April 2002

Introduction

This SOP describes the procedures to follow for the continuous determination of ventilation rate in mechanically ventilated livestock and poultry housing units. The method used for evaluating housing ventilation rate will be the Fan Curve Method (FCM). In this method, the status of fans is monitored (on/off), the static pressure is monitored across a fan or fan bank, and the appropriate fan calibration data is used to determine airflow rate delivery.

Equipment Needed

1. FANS monitoring system

2. SETRA Model 267 or Model 267MR static pressure sensor or equivalent

3. SETRA Model ______ power supply

4. Fan status limit switches Telemecanique Model XCK-P106 (Grainger Model 4B799)

(18.5 in-oz activating torque)

5. NEMA 4X enclosure

6. Miscellaneous wiring circuitry

Procedures

The FANS unit is to be calibrated as per BESS Laboratories (University of Illinois-Urbana Champaign). Once calibrated, the FANS unit becomes the calibrated sensor from which to calibrate all operating fans under test.

All fans in a building will be calibrated a minimum of three times in a calendar year. All calibration work in a housing unit will be conducted after a close-out, once before fans are cleaned and once after fans are cleaned. Each fan tested will be tested twice, separated by a 15-minute interval with simultaneous measurements of static pressure. The average airflow delivery rate for each fan will be recorded, along with the average static pressure measurement. This airflow versus static pressure will be used in future calculations to determine airflow delivery rate. For each fan a set of data will exist for dirty versus cleaned. Three static pressure levels will be tested by artificially adjusting the fresh-air intake system. Static pressures near 5, 25, and 45 Pa (0.02, 0.10, and 0.18 in wg) will be tested. A linear regression equation will be developed to determine the fan curve for each fan, both cleaned and dirty.

Fan Status Monitoring

The operation status for all fans in a housing unit will need to be known. It is recommended that changes or interception of signals from the existing fan control system not be used. Fan status will be determined using limit switches either attached to existing fan shutters or configured as a sail-switch.

If attached to fan shutters, whisker limit switches are recommended. An example set-up using whisker limit switches (Grainger Model 4B799) is shown below:

An alternative whisker switch arrangement for fan airflow activation configured as a sail switch is shown below (Grainger Model 4B804):

Field Installation

It is recommended that a NEMA 4X enclosure be installed in each barn to provide the necessary wiring connections for all limit switches and the static pressure sensor. An example enclosure and wiring connections are shown below:

Limit Switch Wiring

A 2-conductor shielded 18 or 20 gage cable is recommended for each limit switch. The static pressure power supply (SETRA Model ______) delivers approximately 24vdc to the SETRA Model 267 (or 267MR) static pressure sensor and can be used to provide the necessary power to record limit switch operation. Two alternatives exist for wiring the limit switches. In the first method, the voltage sensed from the fan sensor array will vary as the number of operating fans varies. This method requires that the fan sensor switches be recorded as true analog inputs. A second method yields a true TTL-compatible signal requiring only that a digital input signal be recorded. The first method utilizes more expensive analog input data acquisition equipment but does give the user a better chance of determining proper operation of the limit switches. Wiring examples are given below:

Method 1. Variable analog output with sequential fans in operation

Fan On: VDC out: Fan On: VDC out:

0 0.0 1,2,3,4 2.4

1 5.2 1,2,3,4,5 2.0

1,2 3.7 1,2,3,4,5,6 1.7

1,2,3 2.9

Method 2. True binary output signal

Fan On: VDC out: Fan On: VDC out:

0 0.0 1,2,3,4 5.2

1 5.2 1,2,3,4,5 5.0

1,2 5.2 1,2,3,4,5,6 4.2

1,2,3 5.2

Ventilation Rate Calculations

Airflow delivery rate for a housing unit will be determined by:

1. Measuring static pressure

2. Recording fan status

3. Apply FANS calibration data to operating fans

4. Determine housing unit airflow delivery rate using:

Q = S { FCF_i * Fan_i * (m_i*DP + b_i) } for Fans i = 1 to n

where

Q = airflow delivery rate, m³/h (ft³/min)

FCF_i = fan cleanliness factor (maximum=1.0, minimum determined from dirty/clean fan performance)

Fan_i = individual fan status (0 = off, 1 = on)

DP = static pressure difference between room and outside, Pa (in wg)

m_i = slope for regression equation developed using FANS, m³/hr-Pa (ft³/min-in wg)

b_i = intercept for regression equation developed using FANS, m³/hr (ft³/min)

The Fan Cleanliness Factor (FCF) is an estimate of the effect on airflow delivery of dust build-up on fan blades, shutters, and grills. When cleaned at the start of a grow-out period, the FCF=1.0. The FCF during the growth period will be estimated using the following equation:

FCF_i = (1-EF_i) * {(We – W) / (We – Ws)} + EF_i

where

We = ending animal weight, kg (lbs)

Ws = beginning animal weight, kg (lbs)

W = current animal weight, kg (lbs)

EF_i = fan efficiency factor as determined by dirty versus cleaned fan data

= 1.0 for cleaned fan

= a factor determined by the difference in airflow delivery for a dirty versus cleaned fan