Static Pressure Set Point (SP.SP) — This is the static pres- sure control point. It is the point against which the ComfortLink controls compare the actual measured supply duct pressure for determination of the error that is used for PID control. Generally one would set SP.SP to the minimum value necessary for proper operation of air terminals in the condi- tioned space at all load conditions. Too high of a value will cause unnecessary fan motor power consumption at
VFD Minimum Speed (SP.MN) — This is the minimum speed for the supply fan VFD. Typically the value is chosen to main- tain a minimum level of ventilation.
NOTE: Most VFDs have a
VFD Maximum Speed (SP.MX) — This is the maximum speed for the supply fan VFD. This is usually set to 100%.
VFD Fire Speed Override (SP.FS) — This is the speed that the supply fan VFD will use during the pressurization, evacua- tion and purge fire modes. This is usually set to 100%.
Static Pressure Reset Configuration (SP.RS) — This option is used to configure the static pressure reset function. When SP.RS = 0, there is no static pressure reset via an analog input. If the outdoor air quality sensor is not configured (Configura- tion→IAQ→IAQ.CF→OQ.A.C = 0), then it is possible to use the outdoor air quality sensor location on the CEM board to perform static pressure reset via an external 4 to 20 mA input.
Configuring SP.RS = 1 provides static pressure reset based on this CEM 4 to 20 mA input and ranged from 0 to 3 in. wg. Wire the input to the CEM using
=2, there is static pressure reset based on RAT and defined by SP.RT and SP.LM. When SP.RS = 3, there is static pressure re- set based on SPT and defined by SP.RT and SP.LM.
Setting SP.RS to 1, 2 or 3 will give the user the ability to re- set from 0 to 3 in. wg of static pressure. The reset will apply to the supply static pressure set point. The static pressure reset function will only act to reduce the static pressure control point.
As an example, the static pressure reset input is measuring 6 mA, and is therefore resetting 2 mA (6 mA – 4 mA) of its 16 mA control range. The 4 to 20 mA range corresponds
directly to the 0 to 3 in. wg of reset. Therefore 2 mA reset is 2/16 * 3 in. wg = 0.375 in. wg of reset. If the static pressure set point (SP.SP) = 1.5 in. wg, then the static pressure control point for the system will be reset to 1.5 – 0.375 = 1.125 in. wg.
When SP.RS = 4, the static pressure reset function acts to provide direct VFD speed control where 4 mA = 0% speed and 20 mA = 100% (SP.MN and SP.MX will override). Note that SP.CF must be set to 1 (VFD Control), prior to configuring SP.RS = 4. Failure to do so could result in damage to ductwork due to overpressurization. This is the recommended approach if a third party wishes to control the variable speed supply fan. In effect, this represents a speed control signal “pass through” under normal operating circumstances. The ComfortLink con- trol system overrides the third party signal for critical operation situations, most notably smoke and fire control.
Static Pressure Reset Ratio (SP.RT) — This option defines the reset ratio in terms of static pressure versus temperature. The reset ratio determines how much is the static pressure reduced for every degree below set point for RAT or SPT.
Static Pressure Reset Limit (SP.LM) — This option defines the maximum amount of static pressure reset that is allowed. This is sometimes called a “clamp.”
NOTE: Resetting static pressure via RAT and SPT is primarily a constant volume application which utilizes a VFD. The rea- soning is that there is significant energy savings in slowing down a supply fan as opposed to running full speed with supply air reset. Maintaining the supply air set point and slowing down the fan has the additional benefit of working around dehumidification concerns.
Static Pressure Reset Economizer Position (SP.EC) — This option effectively resets ECONOMIN to fully occupied venti- lation position, to account for the drop in static pressure during static pressure reset control. The static pressure reset for the calculation cannot be larger than the supply air static set point (SPSP).
The calculation is as follows:
(Static Pressure Reset/SP.LM) x (ECONOSPR –
ECONOMIN)
As an example, the static pressure reset limit (SP.LM) =
0.75in. wg. The current static pressure reset is set to 0.5 in. wg. The settings for ECONOSPR = 50% and ECONOMIN = 20%.
Table 75 — Static Pressure Control Configuration
ITEM | EXPANSION |
| RANGE | UNITS | CCN POINT | DEFAULT |
SP | SUPPLY STATIC PRESS.CFG. |
|
|
|
|
|
SP.CF | Static Pres. VFD Control? | 0, 1 |
| STATICFG | 0* | |
SP.FN | Static Pres. Fan Control? | Yes/No |
| STATPFAN | Yes* | |
SP.S | Static Pressure Sensor | Enable/Disable |
| SPSENS | Disable* | |
SP.LO | Static Press. Low Range | in. W.C. | SP_LOW | 0 | ||
SP.HI | Static Press. High Range | 0 | - 10 | in. W.C. | SP_HIGH | 5 |
SP.SP | Static Pressure Setpoint | 0 | - 5 | in. W.C. | SPSP | 1.5 |
SP.MN | VFD Minimum Speed | 0 | - 100 | % | STATPMIN | 20 |
SP.MX | VFD Maximum Speed | 0 | - 100 | % | STATPMAX | 100 |
SP.FS | VFD Fire Speed Override | 0 | - 100 | % | STATPFSO | 100 |
SP.RS | Stat. Pres. Reset Config | 0 | - 4 |
| SPRSTCFG | 0 |
SP.RT | SP Reset Ratio (″/dF) | 0 | - 2.00 |
| SPRRATIO | 0.2 |
SP.LM | SP Reset Limit in iwc (″) | 0 | - 2.00 |
| SPRLIMIT | 0.75 |
SP.EC | SP Reset Econo.Position | 0 | - 100 | % | ECONOSPR | 5 |
S.PID | STAT.PRESS.PID CONFIGS |
|
|
|
|
|
SP.TM | Static Press. PID Run Rate | 1 | - 200 | sec | SPIDRATE | 2 |
SP.P | Static Press. Prop. Gain | 0 | - 100 |
| STATP_PG | 20 |
SP.I | Static Press. Intg. Gain | 0 | - 50 |
| STATP_IG | 2 |
SP.D | Static Press. Derv. Gain | 0 | - 50 |
| STATP_DG | 0 |
SP.SG | Static Press. System Gain | 0 | - 50 |
| STATP_SG | 1.0 |
*Some defaults are model number dependent.
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