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Unitary DDC Controller |
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rev. 2008-11-25
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Unitary DDC Controller |
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rev. 2008-11-25
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Existing Conditions
The existing equipment is under pneumatic, electric, or manual control that is very basic and may not work well. With this type of control, equipment runs longer than necessary to cover all possible expected operating conditions. These controls are subject to tampering when they fail to perform well, and cannot be set up with the energy-saving strategies available with modern digital controls.
Retrofit Conditions
We suggest replacing existing controls with a “unitary” automation controller. This type of controller is a standalone unit with input and output capability and a small LCD display and keypad. It would be programmed at the time of installation according to energy-conserving strategies specified by the design engineer. The building operator would be able to use the keypad to change basic settings such as occupancy schedules and temperature setpoints. Generally these controllers are members of product families that can be networked together into facility-wide DDC (Direct Digital Control) systems. DDC systems can include many safety and convenience features such as full graphic terminal operation, remote access via phone line, dial out of alarms, security monitoring, and trending of energy and equipment data.
For the purpose of this study, we are recommending the most cost-effective approach, which is the installation of small local controllers intended to save energy. The decision to connect several units together into a single network can be deferred until clear operating benefits are identified.
Further Benefits
Application Details
For this unit, we recommend the following strategies:
(For Single Zone Air Handler)
| • | Scheduled start/stop with adaptive optimized startup. |
| • | Night setback of space temperature, both heating and cooling. Setpoints adjustable at local terminal. |
| • | Unoccupied mode with fan cycling to maintain setback temperature range and no ventilation. |
| • | Timed setback override (adjustable period). Simple override activation from space sensor. |
| • | PID control of supply air temperature, reset from space. Reset curve endpoints and room sensor authority adjustable from local terminal. |
| • | PID control of free cooling economizer, mixing to 13ºC operator-adjustable setpoint. |
| • | Economizer dry bulb override to minimum position when outside air temperature is above 20ºC. |
| • | Scheduled seasonal lockout for electric baseboard heat. |
| • | Holiday scheduling. |
| • | Night purge during cooling season, when nighttime outside temperature allows. |
| • | Auxiliary output for scheduling associated exhaust fans. |
| • | Auxiliary output for scheduling outdoor security lights. |
| • | Auxiliary output for scheduling domestic hot water recirculation pump. |
| • | Text alarm messages displayed at local terminal. |
(For Single Zone Air Handler, VVT style zone volume control and unit bypass damper)
| • | Scheduled start/stop with adaptive optimized startup. |
| • | Individual control of zone space temperature through volume control boxes. |
| • | Air handler bypass, controlling to duct pressure. |
| • | Night setback of space temperature, both heating and cooling. Setpoints adjustable at local terminal. |
| • | Unoccupied mode with fan cycling to maintain setback temperature range and no ventilation. |
| • | Timed setback override (adjustable period) for each zone. Simple override activation from space sensor.PID control of supply air temperature, reset from space. Reset curve endpoints and room sensor authority adjustable from local terminal. |
| • | PID control of free cooling economizer, mixing to 13ºC operator-adjustable setpoint. |
| • | Economizer dry bulb override to minimum position when outside air temperature is above 20ºC. |
| • | Scheduled seasonal lockout for electric baseboard heat. |
| • | Holiday scheduling. |
| • | Night purge during cooling season, when nighttime outside temperature allows. |
| • | Auxiliary output for scheduling associated exhaust fans. |
| • | Auxiliary output for scheduling outdoor security lights. |
| • | Auxiliary output for scheduling domestic hot water recirculation pump. |
| • | Text alarm messages displayed at local terminal. |
(For Multi Zone Air Handler)
| • | Scheduled start/stop with adaptive optimized startup. |
| • | Individual control of zone space temperature through zone dampers. |
| • | Discriminator strategy, to reset both hot and cold deck temperatures based on greatest zone requirements. |
| • | Night setback of space temperature, both heating and cooling. Setpoints adjustable at local terminal. |
| • | Unoccupied mode with fan cycling to maintain setback temperature range and no ventilation. |
| • | Timed setback override (adjustable period) for each zone. Simple override activation from space sensor.PID control of supply air temperature, reset from space. Reset curve endpoints and room sensor authority adjustable from local terminal. |
| • | PID control of free cooling economizer, mixing to 13ºC operator-adjustable setpoint. |
| • | Economizer dry bulb override to minimum position when outside air temperature is above 20ºC. |
| • | Scheduled seasonal lockout for electric baseboard heat. |
| • | Holiday scheduling. |
| • | Night purge during cooling season, when nighttime outside temperature allows. |
| • | Auxiliary output for scheduling associated exhaust fans. |
| • | Auxiliary output for scheduling outdoor security lights. |
| • | Auxiliary output for scheduling domestic hot water recirculation pump. |
| • | Text alarm messages displayed at local terminal. |
(For Multiple Boiler Heating Plant)
| • | Indoor / outdoor reset of supply water temperature, with sample room temperature adjustment. |
| • | Operator adjustment of reset curve endpoints and room sensor authority. |
| • | Night setback of sampled space temperature or supply water temperature and optimized morning warmup. |
| • | Weekly lead / lag rotation of boilers. |
| • | Heating pump rotation. |
| • | Summer shutdown of boilers and pumps, with daily pump exercise to prevent seizing. |
| • | Holiday scheduling. |
| • | Auxiliary output for scheduling associated exhaust fans. |
| • | Auxiliary output for scheduling outdoor security lights. |
| • | Auxiliary output for scheduling domestic hot water recirculation pump. |
| • | Text alarm messages displayed at local terminal. |
Issues and Concerns
References
Analysis
((Example from CBC Windsor))
AHU |
Situation |
Discharge cfm |
Outside Air % |
Outside Air cfm |
Annual Hours OA Useage |
OA Heating Btu |
Heating Plant Efficiency |
Heating m3 |
OA Cooling Btu |
Cooling Plant COP |
Sensible Heat % |
Cooling and Dehumidification kWh |
HVAC-1 |
Existing |
1,900 |
20% |
380 |
8,760 |
60,066,062 |
65% |
2,624 |
16,487,196 |
1.5 |
50% |
6,441 |
HVAC-1 |
BAS Ventilation Setback |
1,900 |
20% |
380 |
4,380 |
30,033,031 |
65% |
1,312 |
8,243,598 |
1.5 |
50% |
3,220 |
HVAC-1 |
Savings |
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1,312 |
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3,220 |
HDD |
3,388 |
CDD |
930 |
The OA Heating Btu is calculated by:
1.08 x Outside Air CFM x (HDD x 9/5) x 24 x (Annual Hours OA Usage ÷ 8760) = Annual OA Heating BTU
The OA Cooling Btu (Sensible Heat) is calculated by:
1.08 x Outside Air CFM x (CDD x 9/5) x 24 x (Annual Hours OA Usage ÷ 8760) = Annual OA Cooling BTU
The Latent heat is included in the Cooling and Dehumidification kWh by:
=OA Cooling Btu ÷ (3413 x Cooling Plant COP x Sensible Heat %)
*To calculate cooling and dehumidification directly, the formula is:
4.5 x CFM x dh
dh = Delta Enthalpy (Btuh per pound of dry air)
The Psychrometric Chart illustrates these values.