Proper Applications & Sequences for Constant Volume Pressure Dependent Zoning Systems. History

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1 Proper Applications & Sequences for Constant Volume Pressure Dependent Zoning Systems Ryan R. Hoger, LEED AP History VAV systems came into favor for mid and large size facilities in the 1960s and 1970s Save energy Improve comfort ake advantage of building diversity Cooling needed year round for true interior core zones Sequence Main AHU provides morning warm-up heat until RA setpoint is satisfied all zones at 100% design airflow AHU switches to 55 F discharge air controlled cooling zones modulate CFM to controls space temp No AHU heat remainder of day individual zone reheat or baseboard as needed 1

Cooling needed year round for true interior core zones Sequence Main AHU provides morning warm-up heat until RA setpoint is satisfied all zones at 100% design

2 History (con t) What about the small buildings? IGVs and refrigerant capacity controls Not available on packaged RUs AHUs - too expensive Expensive zone level CFM/pressure measurement Lack of consistent cooling load for interior zones he Name Game Constant Volume Zoning Refers to primary air source (RU, AHU, etc.) Pressure Dependent Zoning Zone CFM is dependent upon system pressure Auto-changeover VAV Unlike standard VAV, RU/AHU switches from cooling to heating during the day Bypass VAV No IGV or VFD Shut-off VAV Variable Volume and emperature (VV) Parker 2

of consistent cooling load for interior zones he Name Game Constant Volume Zoning Refers to primary air source (RU, AHU, etc.

3 Variable Volume and emperature VV is called is called variable volume because it delivers a variable volume of air to each zone, as load dictates VV is called variable temperature because the temperature of the air supplied by the central unit varies with time General Application Several zones per system (RU/AHU) Small to medium zone 1/4-2 1/2 tons per zone CFM per zone ypically 3 to 15 zones per system (most manufacturers limit at 32) 3 to 25 tons per system Buildings up to 40,000 sq. ft. 3

varies with time General Application Several zones per system (RU/AHU) Small to medium zone 1/4-2 1/2 tons per zone 100-1000

4 Conceptual Layout ROOFOP HEAING AND COOLING UNI ROOF PS CEILING PLENUM REURN SUPPLEMENAL REHEA REURN HROUGH CEILING PLENUM ZONE 1 ZONE 2 ZONE 3 ZONE 4 VV System Design Steps Figure block cooling/heating loads Do preliminary equipment selection Determine control zones Figure zone cooling/heating loads and CFM requirements Select and position diffusers Some say oversize by 25% to reduce noise Some say size as normal to insure adequate throw Select and position dampers Size to handle zone peak CFM at FPM 4

control zones Figure zone cooling/heating loads and CFM requirements Select and position diffusers Some say oversize by 25% to

5 VV System Design Steps (con t) Layout bypass system Position thermostats Size ductwork Main supply and return = unit CFM Branch = zone peak CFM Select supplementary heaters Final equipment selection Do not oversize equipment! Define control wiring requirements and routing Control riser wiring drawings ypical Layout DH-3 AC1 M W L 52/18 52/18 DG /14 20/14 10"Ø 16/14 YP. 8" YP. 10" YPICAL HO WAER SUPPLEMENARY HEAER YP. 10" AH-2 AC2 20/14 20/14 16/ YP. 8" DG-3 DG-3 YP. 10" 7 16/14 5 DH-3 DH-3 YP. 10" 6 YP. 8" 5

Define control wiring requirements and routing Control riser wiring drawings ypical Layout DH-3 AC1 M W L 52/18 52/18 DG-3 4 3

6 Bypass - System Pressure Control Maintains system static pressure to insure adequate airflow into the zones and avoids over pressurization Size bypass adequately Bypass CFM = unit CFM - smallest zone CFM Minimum of 75% of unit CFM Select at 1500 FPM Avoid short-circuiting Facilitate mixing of bypass air with return air Plenum return preferred method VFD is acceptable if air source has hydronic heating and cooling ONLY Return Air Path and Bypass Plenum return design provides better mix of return air with supply air Ducted return provides better latent temperature control in humid environment Can cause nuisance equipment trips resulting in loss of comfort Static Pressure ubing RU Bypass Damper Do not place bypass directly beneath unit RU Bypass Damper Back Draft Damper Static Pressure ubing 6

heating and cooling ONLY Return Air Path and Bypass Plenum return design provides better mix of return air with supply air Ducted return provides better latent temperature control in humid

7 Ceiling Plenum Return Layout SAIC PRESSURE SENSOR & BYPASS DAMPER ACUAOR ROOFOP UNI BYPASS DAMPER WIH SHOR DUC SUPPOR PROPERLY SAIC PRESSURE UBING AIM BYPASS DAMPER DISCHARGE AWAY FROM REURN INLE AVOID REURN GRILLES IN CLOSE PROXIMIY O BYPASS DISCHARGE AIR PAH SAIC PRESSURE PICKUP LOCAE PICKUP IN AREA OF LEAS URBULENCE, 5 DUC DIAMEERS DOWNSREAM OF BYPASS AKEOFF BU UPSREAM OF FIRS ZONE AKEOFF OR MAJOR JUNCION AVOID ELBOWS AND EES Ducted Return Layout REURN BACKDRAF DAMPER LOCAE REURN/BYPASS JUNCION A MINIMUM OF 15 F. FROM UNI INLE BYPASS DAMPER ROOFOP UNI AVOID HE EMPAION O INSALL A SHOR-CIRCUI BYPASS HERE. I WILL CAUSE NUISANCE RIPS WIH ZONE CAPACIY INERRUPION SAIC PRESSURE SENSOR & BYPASS DAMPER ACUAOR SAIC PRESSURE UBING SAIC PRESSURE PICKUP LOCAE PICKUP IN AREA OF LEAS URBULENCE, 5 DUC DIAMEERS DOWNSREAM OF BYPASS AKEOFF BU UPSREAM OF FIRS ZONE AKEOFF OR MAJOR JUNCION AVOID ELBOWS AND EES 7

OR MAJOR JUNCION AVOID ELBOWS AND EES Ducted Return Layout REURN BACKDRAF DAMPER LOCAE REURN/BYPASS JUNCION A MINIMUM OF 15 F.

8 Leaving Air emperature Protection As more air bypasses, the RU/AHU discharge temperature will continue to drop (cooling mode) or rise (heating mode) System should stage down mechanical equipment regardless of zone temperatures being satisfied Cool - 2 nd stage at 50ºF and 1 st stage at 45ºF Heat - 2 nd stage at ºF and 1 st stage at ºF System Mode Selection One (adj.) or more zones must be calling to start heating or cooling usually 25% of total # of zones All zones must satisfy to clear mode Allow auto changeover from heating/cooling if opposite mode has greater demand for 30 (adj.) minutes Bypass damper at 100% open/bypass until duct temp increases above 65ºF (heat) or decreases below 80ºF (cool) Allows supply air to be preconditioned before delivery to zones Minimum heat and cool run time 3 minutes acceptable for most HVAC equipment Heat pumps should be 5 minutes 8

) or more zones must be calling to start heating or cooling usually 25% of total # of zones All zones must satisfy to clear mode Allow auto changeover from heating/cooling if opposite mode has

9 Zone Ventilation Control Allows damper to modulate to provide ventilation airflow when: When system not in heat or cool mode Zone does not have demand Supply air temp is neutral (between 65 F and 80 F) Damper must be allowed to fully shut when RU/AHU is operating in an undesired mode Do not implement minimum zone damper positions CO2-based Demand Controlled Ventilation (DCV) Like a VAV, VV should be zone level DCV RA CO2 not acceptable for zoned systems A wall-mounted CO2 sensor can cover up to 5,000 ft 2 of open space Zone should first open zone damper to satisfy CO2 setpoint utilizing air already in the duct system OA damper should respond to the zone with the largest deviation from zone CO2 setpoint 9

Controlled Ventilation (DCV) Like a VAV, VV should be zone level DCV RA CO2 not acceptable for zoned systems A wall-mounted CO2 sensor can cover up to 5,000 ft 2 of open space

10 Supplemental Heat Ducted and non-ducted heat types include: 2 position (open/closed) hot water heat 1 to 3 stages of electric heat Modulating hot water heat Modulating electric heat Solid State Relays (SSR) Combination 2 position baseboard w/ ducted staged heat Zone should call for supplemental heat before calling for RU/AHU heat Lockout based on OA Overhead heating - size reheat for 90ºF discharge Fan Powered Boxes Not common on VV type systems Can be used for perimeter or other zones with heating loads Sequence same as when used on VAV Series fans run continuously Downsize AHU supply fan selection Parallel fans run as the 1 st stage of zone heat and use warm plenum air 10

Lockout based on OA Overhead heating - size reheat for 90ºF discharge Fan Powered Boxes Not common on VV type systems Can be used for perimeter or other zones with

11 Internet Accessible View and modify data Perform system diagnostics Send alarm messages Dedicated PC for BAS not required around the world! Air Balancing Please see the supplemental document. Use in conjunction with industry standard balancing guidelines, as published by ABB or other reputable balancing organizations. Command the bypass damper closed and VV dampers open Adjust supply fan to achieve the desired system CFM Adjust the maximum damper position to provide the required design maximum airflow to each zone start with zones closest to RU/AHU Set the fan speed setting for each box (fan powered boxes only) Calibrate the duct static pressure transducer for the bypass Calibrate the building static pressure transducer for the exhaust fans (if applicable) 11

Command the bypass damper closed and VV dampers open Adjust supply fan to achieve the desired system CFM Adjust the maximum damper position to provide the required design maximum airflow to

12 Air Balancing (con t) Set the OA minimum position for the RU/AHU Set the duct static pressure setpoint for the bypass controller Set the building static pressure setpoint for the exhaust fans (if applicable) Set the damper position for reheat (if applicable) for each box Route a courtesy copy of the balancing report to controls contractor so any setting changes can be preserved during future service calls. Do s and Don ts Don t apply to HVAC units over 20 tons Don t reduce the quantity of RU/AHUs as compared to single zone constant volume system Don t oversize RU/AHU Do install a XV Don t mix core interior zones on the same system as exterior zones Same rule for mixing exposures (east and west on the same unit, etc.) Exception: If you install and run supplemental heat in all of the perimeter zones Don t install the bypass damper too close to the HVAC unit Don t locate the bypass discharge near plenum return grills Do specify the complete scope of air balancing And the most common problem. Don t specify or implement minimum damper positions 12

13 Ryan R. Hoger, LEED AP hanks to: 13

NEBB STANDARDS SECTION-8 AIR SYSTEM TAB PROCEDURES

NEBB STANDARDS SECTION-8 AIR SYSTEM TAB PROCEDURES 8.1 INTRODUCTION Testing, adjusting, and balancing of HVAC systems can best be accomplished by following a series of systematic procedures. The NEBB TAB