CCS Design Manual Section 8

BCBC Client Comfort System (CCS) - Design Manual

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CCS SEQUENCES OF OPERATION

Description

This example illustrates how the GENERIC START UP LOGIC is compared to a traditional SEQUENCE OF OPERATION. The overall logic for the system is split into sections. In each, the GENERIC START UP LOGIC is listed first, followed immediately by the corresponding SEQUENCE OF OPERATION wording in "normal" English.

The system selected is the BCBC standard system VAV:J. It is a variable air volume system with an outdoor air economizer, hot water heating coil, 2-stage direct expansion cooling coil, and supply and return fans each with a variable speed drive.

1.3 Supply Fan

(A) Supply Fan (SF_PG)

GENERIC START UP LOGIC
      IF RF ON-FOR 30 SEC THEN
           START SF
      ELSE STOP SF

      IF SAP > 30 THEN
           SF_S = ON
      ELSE SF_S = OFF 
SEQUENCE OF OPERATION

If the return fan has been commanded on for 30 seconds, the supply fan is enabled by the DDC panel by sending an "on" signal to the ASD; otherwise, disable the supply fan. If the supply fan is already "ON", then a command to energize will maintain the status quo; and vice-versa when the fan is already "OFF".

If the static pressure in the supply duct (SAP) is greater than 30 Pa as measured by the duct pressure sensor, the supply fan status point will be "ON", otherwise the supply fan status is "OFF".

The supply fan program includes software to measure and display run hours and trend logs.

(B) Supply Fan ASD ( Adjustable Speed Drive )

GENERIC START UP LOGIC
        IF SF ON THEN
             SF_ASD = SAP_CO
        ELSE SF_ASD = 0
SEQUENCE OF OPERATION

If the supply fan (SF) control point is energized, then the output to the speed control portion of the ASD will equal the output of the SAP controller (SAP_CO). Input to SAP_CO is SAP and setpoint is SAP_SP. The rate of speed change is controlled internally by the ASD.

If the supply fan is not energized the signal to the supply fan ASD is zero.

2.2 Return Fan

(A) Return Fan (RF_PG)

GENERIC START UP LOGIC
        IF WS ON OR RT_AVG <14 then start rf if ws off and rt_avg> 16 THEN
	     STOP RF
SEQUENCE OF OPERATION

The operation of the return fan is controlled by a weekly schedule (WS) in the software in the panel. When the WS is "ON" ( building is occupied or if the average room temperature is below 14(C, then energize the return fan (RF).

If the WS is "OFF" and the average room temperature is higher than 16(C, then de-energize the RF.

(B) Return Fan ASD

GENERIC START UP LOGIC
        BSP_SP = ____ DEFAULT = 20 Pa
        IF RF ON THEN
	     RF_ASD = SF_ASD - (BSP_SP - BSP)
        ELSE RF_ASD = 0
SEQUENCE OF OPERATION

The return fan speed is controlled to maintain the building static pressure (BSP) at a positive value ( relative to outside ); a default value of 20 Pascals ( Pa ) has been selected as the BSP setpoint (BSP_SP).

If the return fan has been commanded "ON" ( there is no return fan status point, so this indication cannot come directly from status ), then theDDC output ( 0 - 100% ) to the RF speed controller ( RF_ASD ) is equal to the percentage output value to the supply fan ASD minus a numerical value equal to the building static pressure setpoint minus the building static pressure. The rate of speed change is controlled internally by the ASD. If the return fan has been commanded "OFF", then the return fan ASD output is set to zero.

3.2 Mixed Air Damper

(A) Part 1 of the logic.

GENERIC START UP LOGIC
        MAD_MIN = ____ DEFAULT = 30%
        DO EVERY 3 S RAMP = RAMP + 1%
        IF SF OFF THEN
	     RAMP = 0%
        IF RAMP > 100% THEN
             RAMP = 100% END DO
SEQUENCE OF OPERATION

The mixed air damper minimum (MAD_MIN) is a variable for selecting outside air damper minimum position; the default value is 30%. The variable "RAMP" controls the speed at which the damper can open; set at a 1% increase every 3 seconds.

If the supply fan is "OFF", then the "RAMP" is reset to 0%. If the RAMP calculation results in an outside air damper position greater than 100%, then set "RAMP" equal to 100%.

(B) Part 2 of the Logic

GENERIC START UP LOGIC
        IF SF_S ON AND WS ON AND FRZ OFF THEN
	     IF CLG_MODE ON OR HTG _MODE ON THEN
	          IF RAT 
SEQUENCE OF OPERATION

If the supply fan status is "ON", the weekly schedule is "ON", and the freeze control is "OFF" ( ie. there is no freeze condition detected ), then:

If there is a call for heating ( "HTG_MODE" is "ON" ), then set MAD to the minimum outside air position;

If there is a call for cooling ( "CLG_MODE" is "ON" ) and the return air temperature is lower than the outside air temperature, then set MAD to the minimum outside air position;

If there is a call for cooling and the return air temperature is equal to or higher than the outside air temperature, then set MAD to 100% outside air.

If there is no call for either heating or cooling ( both "HTG_MODE" and "CLG_MODE" are "OFF" ), then control the mixed air damper from the maximum value of either the MAD_MIN variable or the output of the software controller "MAD_CO" (which uses SAT as the input and SAT_SP as the setpoint). Also limit the rate of damper opening on start up, in order to prevent the freeze protect from tripping, by controlling the mixed air damper from the minimum value of either the mixed air damper position (from previous line) or the value of the RAMP variable.

Under all other conditions, the MAD is set to 0% outside air.

The mixed air damper program includes software to measure, display and store trend logs of damper position, mixed air temperature, freeze, and supply fan status.

4.3 Cooling

The supply fan must be running ( status in "ON" ) or mechanical cooling cannot be energized.

(A) First Stage Cooling

GENERIC START UP LOGIC
        IF SF_S ON THEN
	     IF RT_AVG > RT_SP + 1.3 OR
	RT_MAX > RT_SP + 2.0 THEN
	     CLG_MODE = ON, START DX1
	IF RT_AVG 
SEQUENCE OF OPERATION

If the average room temperature is higher than the room temperature setpoint plus 1.3(C or if the maximum room temperature is higher than the room temperature setpoint plus 2.0(C, the cooling mode is set to "ON" and the first stage of mechanical cooling ( "DX1" ) is energized.

When the average room temperature is less than the room temperature set point plus 0.8(C and the maximum room temperature is less than the room temperature set point plus 1.5(C, the cooling mode is "OFF" and the first stage of mechanical cooling is de-energized.

(B) Second Stage Cooling

GENERIC START UP LOGIC
        IF SF_S ON THEN
	     IF RT_AVG > RT_SP + 1.5 OR
             RT_MAX > RT_SP + 2.3 OR
	     DX1 ON-FOR 15 MIN THEN
	          START DX2
	     IF RT_AVG 
SEQUENCE OF OPERATION

If the average room temperature is higher than the room temperature setpoint plus 1.5(C or if the maximum room temperature is higher than the room temperature setpoint plus 2.3(C or if the first stage of cooling has been on for 15 minutes or more, then the second stage of mechanical cooling ("DX2") is energized.

If the average room temperature is less than the room temperature setpoint plus 1.0(C and the maximum room temperature is less than the room temperature setpoint plus 1.7(C, then de-energize the second stage of cooling.

5.2 Heating

(A) Heating (HTG_PG)

GENERIC START UP LOGIC
        IF SAT <10 then htg_mode="ON," hcv="HCV_CO" if sat> 14 THEN
	     HTG_MODE = OFF, HCV = 0
SEQUENCE OF OPERATION

If the supply air temperature ( SAT ) is less than 10(C, the heating mode is energized and the heating coil valve is controlled by a software controller in the DDC panel ( "HCV_CO" ) to meet the SAT setpoint of 12(C (see points list). If the supply air temperature rises above 14(C, the heating mode is de-energized and the heating coil valve closes.

(B) Heating Coil Pump

GENERIC START UP LOGIC
        IF HCV > 15% OR MAT <3 then start hcp if hcv < 2% and mat> 7 THEN
	     STOP HCP
SEQUENCE OF OPERATION

If the heating coil valve is more than 15% open, or the mixed air temperature ("MAT") is less than 3(C, then start the heating coil pump. If the heating coil valve is less than 2% open, and the MAT is higher than 7(C, then stop the heating coil pump.

The heating program includes software to measure, display and store trend logs of heating coil valve position, supply air temperature setpoint, supply air temperature, and heating coil pump operation.

11.3 Supply Air Temperature

GENERIC START UP LOGIC
        RT_SP = _____ DEFAULT = 22
        SAT_SP = 18 - ((RT_AVG - RT_SP) * 4 )
SEQUENCE OF OPERATION

A room temperature setpoint ("RT_SP") is selected (default value is 22(C). The supply air temperature set point is set equal to 18(C minus (4 times (the average room temperature minus the room temperature setpoint))

The supply air temperature program includes software to measure, display and trend the supply air temperature and setpoint, and the room temperature and setpoint.

12.3 Supply Air Pressure

GENERIC START UP LOGIC
        SAP_SP = _____ DEFAULT = 100 Pa
SEQUENCE OF OPERATION

A supply duct static pressure setpoint ("SAP_SP") is selected (default value is 100 Pascals). The supply air pressure program ustilizes a software controller ("SAP_CO") to control the supply fan ASD to maintain the supply duct static pressure setpoint. Refer back to 1.3 (B) Supply Fan ASD for the controlling logic.

The supply air pressure program includes software to measure, display and trend the supply air pressure and setpoint.

8_5.DOC Updated: 95/12/06 by AJZ Copyright © British Columbia Buildings Corporation, September 1994

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