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Direct Digital Controls (DDC)
The Direct Digital Control (DDC) measure would mandate DDC systems for certain building applications that are currently not required. By expanding the scope of applications requiring DDC, energy management data would be more readily available allowing for more efficient systems operations and the implementation of effective energy efficiency strategies. The measure would also specify the minimum capability of such mandated DDCs to ensure the full benefit of DDC for energy management.
Existing 2013 Title 24 does not have any requirements for Direct Digital Controls. It does define Direct Digital Controls as:
DIRECT DIGITAL CONTROL (DDC) is a type of control where controlled and monitored analog or binary data, such as temperature and contact closures, are converted to digital format for manipulation and calculations by a digital computer or microprocessor, then converted back to analog or binary form to control mechanical devices.
This measure would add DDC requirements to Section 120.2 – Required Controls for Space-Conditioning Systems. The requirement of DDCs will apply to both new buildings and retrofits (alterations and additions) with HVAC systems of a set minimum size, see proposed Table 120.2-A DDC Applications and Qualifications below.
|New building||Air-handling system and all zones served by the system||Individual systems supplying more than three zones and with fan system bhp of 10 hp (7.45 kW) and larger|
|New building||Chilled-water plant and all coils and terminal units served by the system||Individual plants supplying more than three zones and with design cooling capacity of 300,000 Btu/h (87.9 kW) and larger|
|New building||Hot-water plant and all coils and terminal units served by the system||Individual plants supplying more than three zones and with design heating capacity of 300,000 Btu/h (87.9 kW) and larger|
|Alteration or addition||Zone terminal unit such as VAV box||Where existing zones served by the same air-handling, chilled-water, or hot-water system have DDC|
|Alteration or addition||Air-handling system or fan coil||Where existing air-handling system(s) and fan-coil(s) served by the same chilled- or hot- water plant have DDC|
|Alteration or addition||New air-handling system and all new zones served by the system||Individual systems with fan system bhp of 10 hp (7.45 kW) and larger and supplying more than three zones and more than 75% of zones are new|
|Alteration or addition||New or upgraded chilled-water plant||Where all chillers are new and plant design cooling capacity is 300,000 Btu/h (87.9 kW) and larger|
|Alteration or addition||New or upgraded hot-water plant||Where all boilers are new and plant design heating capacity is 300,000 Btu/h (87.9 kW) and larger|
The DDC systems that are mandated by proposed Table 120.2-A, above, shall have the following capabilities but not limited to:
- Monitor zone and system demand for fan pressure, pump pressure, heating, and cooling.
- Transfer zone and system demand information from zones to air distribution system controllers and from air distribution systems to heating and cooling plant controllers.
- Automatically detect those zones and systems that may be excessively driving the reset logic and generate an alarm or other indication to the system operator.
- Readily allow operator removal of zone(s) from the reset algorithm.
- For new buildings, the DDC system shall be capable of trending and graphically displaying input and output points.
Note that buildings with mandated DDC systems will trigger another section of Title 24, Section 120.2(h), requiring Automatic Demand Response (ADR) capabilities, therefore the DDC system will have to have to incorporate ADR capabilities as specified in Title 24, Section 120.2(h).
The fan efficiency measure will propose using a new metric known as the Fan Efficiency grade (FEG), a metric adopted by ASHRAE and created by the Air Movement and Control Association (AMCA). The fan efficiency measure will require a minimum FEG of 67, and the total efficiency of the fan at the design point of operation shall be within 15 percentage points of the maximum total efficiency of the fan.
This will be a prescriptive measure that will apply to all fans minus the following exceptions:
- Single fans with a motor nameplate horsepower 5 hp (4 kW) or less.
- Multiple fans in series or parallel (e.g., fan arrays) that have a combined motor nameplate horsepower of 5 hp (4 kW) or less and are operated as the functional equivalent of a single fan.
- Fans that are part of equipment listed under Section 220.127.116.11 “Minimum Equipment Efficiencies – Listed Equipment – Standard Rating and Operating Conditions.”
- Fans included in equipment bearing a third-party-certified seal for air or energy performance of the equipment package.
- Powered wall/roof ventilators (PRV)
- Fans outside the scope of AMCA 205
- Fans that are intended to only operate during emergency conditions
The proposed Elevator Lighting and Ventilation measure is to meet ASHRAE 90.1 2013 section 10.4.3. The Lighting in the cab (not including signals and displays) shall not have an efficacy less than 35 lumens per Watt. Cab ventilation fans for elevators without air conditioning shall not consume over 0.33 Watt per cfm at maximum speed. After being unoccupied at rest with the doors shut for over 15 minutes, cab interior lighting and ventilation shall be de-energized until required for operation.
The escalator and moving walkway speed control measure would require escalators and moving walkways to automatically slow down to the minimum permitted speed in accordance with ASME A17.1/CSA B44, or applicable local code, when not conveying passengers. This measure would conserve energy when these motorized walkways are not in use. There are no existing Title 24 requirement for escalators and moving walkways.
ASME A17.1/CSA B44 v.2010 lists the requirements for escalators and moving walkways with variable speeds:
- Acceleration and deceleration shall not exceed 1.0 ft/sec2
- Rated Speed (100 ft/min) is not exceeded
- Minimum speed not less than 10 ft/min
- Passenger Detection provided at both landings
- Deceleration does not occur until 3x time for passenger transfer between landings
- Means to detect failure of passenger detection.
- If failure is detected, run at full rated speed only