Air Side Economizers and Energy Recovery - Improvements and New Regulations. Richard Lord

Transcription

1 Air Side Economizers and Energy Recovery - Improvements and New Regulations Richard Lord

2 Introduction For commercial buildings the use of outside air for cooling and ventilation is an important consideration in the operation and overall system efficiency ASHRAE 62.1 defines the ventilation requirements for occupied spaces and is one of the primary methods to control indoor air quality Energy Standards like ASHRAE 90.1, Title 24 and the IECC define requirements for the use of outside air to provide free cooling to the space ASHRAE 90.1 also defines when energy recovery is required to recovery energy from high amount of ventilation and exhaust air Economizers and Energy Recovery are not factored into the standard ratings like EER, IEER, and SEER for HVAC products but are an import factor in the overall annualized efficiency of the system. Typically the outside air for ventilation and economizer free cooling are handled thru outside air and return dampers. There have been several studies that have shown significant problems with the dampers and related controls 2

3 Agenda Airside Economizers Airside Economizer Technology Review of economizer and damper control problems Review of commercial building load profiles Benefits of Economizers Improvements in Economizers New economizer regulations Energy Recovery Energy Recovery Technology New Energy Recovery Products Benefits of Energy recovery Combined Efficiency Rating Procedures New Regulations for Energy Recovery 3

4 Airside Economizers 4

5 Airside Economizer Technology Shown is a typical packaged rooftop with an airside economizer 5

6 Economizer Problems Several field studies have been conducted and the following problems have been found with economizers Damper Linkage Failure Economizer damper motor not functioning Economizer disconnected Minimum ventilation position not properly set Changeover sensor inaccuracy and failure Solar impact on changeover temperature sensor failure Supply temperature sensor failure and inaccuracy Integrated Economizer controls and operational issues Building pressurization (improper exhaust/relief) Exhaust air recirculation Damper blade leakage (outside and return) Lack of Maintenance Lack of and improper commissioning 6

7 Economizer Problems Damper Linkage Problems Damper Leakage Problems Economizer Hoods and Maintenance Problems Sensor and Actuator Problems High Limit Controls and Sensor Accuracy Integrated Economizer and Controls Problems 7

8 Typical Commercial Building Load Profile Economizer only Operation 1322 hrs Integrated Economizer Comp + Economizer 1316 hrs Mechanical Cooling No Economizer 73 hrs 8

9 USA Weather Zones Fairbanks 8 Duluth 7A Helena 6B Chicago 5A Burlington 6A Salem 4C Boise 5B Baltimore 4A San Francisco 3C Phoenix 2B Albuquereque 4B El Paso 3B Houston 2A Memphis 3A Miami 1A 9

10 Economizer Operating Hrs The following chart shows the operating hr profiles for a small office building in each of the ASHRAE climate zones and benchmark cities Economizer Only Integrated Mechanial Only 8 - Fairbanks 7 - Duluth 6B - Helena 6A - Burlington 5C - Vancouver 5B - Boise 5A - Chicago 4C - Salem 4B - Albuquerque 4A - Baltimore 3C - San Francisco 3B - El Paso 3A - Memphis 2B - Phoenix 2A - Houston 1B - Riyadh 1A - Miami Annual hrs 10

11 Economizer Annual Energy Savings The following chart shows the energy savings for an integrated economizer vs. a small rooftop unit without an economizer on a small office building 8 - Fairbanks 7 - Duluth 41.97% 44.73% 6B - Helena 37.96% 6A - Burlington 31.99% 5C - Vancouver 41.05% 5B - Boise 37.13% 5A - Chicago 29.41% 4C - Salem 4B - Albuquerque 37.24% 35.69% 4A - Baltimore 30.70% 3C - San Francisco 39.71% 3B - El Paso 26.93% 3A - Memphis 13.28% 2B - Phoenix 2A - Houston 17.19% 15.77% 1B - Riyadh 11.37% 1A - Miami 4.95% 0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00% 35.00% 40.00% 45.00% 50.00% 11

12 Economizer Improvements The benefits of the use of economizers are significant but prior studies have shown actual savings in the field were not being obtained due to problems previously mentioned. So the industry has been working to improve the economizers and their performance Some of the things the industry has implemented are; New drive configurations using gears New digital economizer with electronic feedback Low leak dampers on outdoor and return air New sensors with digital signals and error detection New control logic for integrated control Reliability Cycle Testing Factory run testing Outdoor cfm sensors New micropressor based controllers Integrated displays and error detection 2 speed Economizers for reduced energy use Integration with energy recovery 12

13 Economizer Improvements New Configurations Blade Seals Leakage Testing Gear Drive Economizers Life Testing 13

14 19:27:32 19:28:50 19:30:08 19:31:26 19:32:45 19:34:03 19:35:21 19:36:39 19:37:56 19:39:13 19:40:30 19:41:48 19:43:05 19:44:23 19:45:40 19:46:57 19:48:15 19:49:32 19:50:50 19:52:06 19:53:24 19:54:41 19:55:59 19:57:17 19:58:35 19:59:53 20:01:11 20:02:28 20:03:46 20:05:04 20:06:22 20:07:40 20:08:57 20:10:15 20:11:33 20:12:50 20:14:07 20:15:25 20:16:42 20:17:59 20:19:17 20:20:34 20:21:51 20:23:08 Economizer Improvements Advanced controllers With integrated diagnostics New digital sensors Many new smart economizer controllers : 57 ambient, free cooling, Y1 then Y2, B stayed off due to SAT Low Cool SAT Setpoint = 60 High Cool SAT Setpoint = 50 SAT Min High = 55 SAT Min Low = ECONOCMD ECONOPOS OA_TEMP SAT_DISP COMP_A COMP_B Y1 Y New high limit control concepts New integrated control logic to eliminate damper cycling 14

15 Economizer ASHRAE 90.1 Size Requirements ASHRAE 90.1 has expanded the requirements for economizers to additional zones and to smaller sizes Zone Benchmark City Volume Distribution Economizer Required Proposal 1A Miami 1.18% None None None 1B Riyadh 0% None None None 2A Houston 8.84% None 54,000 Btu/hr 54,000 Btu/hr 2B Phoenix 3.88% 135,000 Btu/hr 54,000 Btu/hr 36,000 Btu/hr 3A Memphis 8.74% None 54,000 Btu/hr 36,000 Btu/hr 3B El Paso 8.32% 65,000 Btu/hr 54,000 Btu/hr 36,000 Btu/hr 3C San Francisco 8.68% 65,000 Btu/hr 54,000 Btu/hr 36,000 Btu/hr 4A Baltimore 13.67% None 54,000 Btu/hr 36,000 Btu/hr 4B Albuquerque 1.44% 65,000 Btu/hr 54,000 Btu/hr 36,000 Btu/hr 4C Salem 2.15% 65,000 Btu/hr 54,000 Btu/hr 36,000 Btu/hr 5A Chicago 21.08% 135,000 Btu/hr 54,000 Btu/hr 36,000 Btu/hr 5B Boise 5.29% 65,000 Btu/hr 54,000 Btu/hr 36,000 Btu/hr 5C Vancouver 0% 65,000 Btu/hr 54,000 Btu/hr 36,000 Btu/hr 6A Burlington 10.43% 135,000 Btu/hr 54,000 Btu/hr 36,000 Btu/hr 6B Helena 2.54% 65,000 Btu/hr 54,000 Btu/hr 36,000 Btu/hr 7 Duluth 2.33% 135,000 Btu/hr 54,000 Btu/hr 36,000 Btu/hr 8 Fairbanks 1.42% 135,000 Btu/hr 54,000 Btu/hr 36,000 Btu/hr No change Improved 15

16 % Annual Tons with Economizer Economizer Size Impact Analysis The chart shows the impact of the size requirements and is the percent sales by total annual tons that would require an air economizer for Unitary Products 90.0% 80.0% 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% Annual Capacity with Economizers 85.3% 56.7% 22.8% ASHRAE 90.1 Standard 16

17 ASHRAE 90.1 Economizer Requirements Addition of a 2 speed fan requirement for units >65K which also requires a 2 speed economizer 110,000 Btu/hr effective 1/1/ ,000 Btu/hr effective 1/1/ ,000 Btu/hr effective 1/1/2016 DX units that control the capacity of the mechanical cooling directly based on occupied space temperature shall have a minimum of 2 stages of mechanical cooling capacity per the following effective dates: 75,000 Btu/h Rated Capacity Effective 1/1/ ,000 Btu/h Rated Capacity Effective 1/1/2016 For VAV units the following capacity staging is required Table DX Cooling Stage Requirements for Modulating Airflow Units Rating Capacity 65,000 Btu/h and <240,000 Btu/h Minimum Number of Minimum Compressor Mechanical Cooling Stages Displacement 1 3 stages 35% of full Load 240,000 Btu/h 4 stages 25% full load Also Required by Title 24 17

18 Standard Integrated Economizer Requirements Economizer systems shall be integrated with the mechanical cooling system and be capable of providing partial cooling even when additional mechanical cooling is required to meet the remainder of the cooling load. Controls shall not false load the mechanical cooling systems by limiting or disabling the economizer or any other means, such as hot gas bypass except at the lowest stage of mechanical cooling. Units that include an air economizer shall comply with the following: a. Unit controls shall have the mechanical cooling capacity control interlocked with the air economizer controls such that the economizer is at the 100% open position when mechanical cooling is on and the economizer does not begin to close until the leaving air temperature is less than 45 F. Also Required by Title 24 18

19 Economizer Improvements Additional changes are also being made to the high limit control options Some of the options like differential enthalpy are being eliminated Others are having the setpoints changes Tolerances have been added to the temperature sensors Accuracies are also being added for high limit sensors Drybulb Sensors = +/- 2 F Enthalpy Sensors = +/- 3 Btu/lbm 19

20 Title Economizer Diagnostics All air-cooled unitary direct-expansion units, equipped with an economizer and mechanical capacity at AHRI conditions of greater than or equal to 54,000 Btu/hr shall include a Fault Detection and Diagnostics (FDD) system The controller shall provide system status by indicating the following conditions Air temperature sensor failure/fault Not economizing when it should Economizing when it should not Damper not modulating Excessive outdoor air In addition the controller shall have a manual control test routine The standard also requires factory certified function testing or field commissioning testing per a defined test procedure 20

21 Energy Recovery 21

22 What is Energy Recovery Energy Recovery uses the exhaust air to partially condition the incoming outdoor air before additional conditioning (cooling or heating) is provided by an HVAC units. It can be used to cool and dehumidify the outdoor air in warm seasons and heat and humidify the outdoor air in cool seasons. There are several types of Energy recovery devices as shown Desiccant heat wheel device Plate Heat Exchanger Device Exhaust Air Return Air Ventilation Air Supply Air Fan 22

23 Typical Packaged ERV Rooftop Package Rooftop Unit Indoor Fan RTU Heating Section Evaporator Mixed Air = RA2 + Outdoor Air Pre-cooled, dehumidified and/or heated Ventilation Air ERV module Enthalpy wheel Outdoor Air Exhaust Air Supply Air Return Air / Exhaust Air Diverter Dampers Return Air Replaceable Filters Airflow Sensing Module 23

24 Typical ERV Section Integral Filters Economizer Bypass Damper Booster Fans Serviceable Energy Recovery Wheel Cleanable Wheels 24

25 Typical Building Outside Air Rates An important factor in the use of energy recovery is the amount of outside air required for building ventilation rates Shown below is a summary of ventilation rates as required by ASHAE 62.1 for typical commercial buildings Venitlation Air Requirements Building %OA Large Office 16.01% Medium Office 13.37% Small Office 23.10% Warehouse 25.76% Retail 65.06% Strip Mall 62.08% Prim. School 75.27% Sec. School 69.17% Grocery 21.57% Fast Food 33.67% Restaurant 36.24% Hospital 54.69% Outpatient Health Care 49.86% Motel 20.38% Hotel 23.25% 25

26 Industry Rating and Certification Standards There are several standards and certification programs that apply to the components used in a packaged unit equipped with energy recovery AHRI 210/ w/addendum 2 <65,000 Btu/hr Packaged and Split Systems AHRI 340/ w/addendum 2 >65,000 Btu/hr Rooftops AHRI 1060 (I-P)-2011 Air to Air Energy Recovery AHRI Guideline V (I-P)-2011 ESIA - Energy Independence and Security Act of 2007 Motor Efficiencies 26

27 AAHX Example Combined Efficiency Hybrid Unit Exhaust Blower Return Air Plenum Balance of Unitary Air Conditioner ERV Unitary Air Conditioner ERV Recovered Energy Efficiency Ratio RTU Energy Efficiency Ratio RER Net conditioningrecovered by ERV Total electricalpower consumedby ERV RER Net conditioningcapacity of RTU Office Code Document Code 0 EER Total electric power by RTU EER CEF = Combined Efficiency Factor Example: 48HC-24 + EnergyX = System CEF (30 ton system) EER & RER = CEF 12.0 & = System EER for a 30 ton total system 27

28 EER or CEF Efficiency Comparison (ERV Example) Example shows how over the operating range a hybrid unit like an ERV/Rooftop can have further improvements at non standard rating conditions Base Rooftop Unit EnergyX Model: 48PGDC12-A-6 48PGDC12-A-6-T Location: Tampa, FL Tampa, FL Altitude (ft) 0.0 ft 0.0 ft CFM Ext static press: 0.75" 0.75" Ventilation Air: 50% or less (economizer) 50% OA (1750 cfm) CEF vs Application EER Combined Rating Improvement Base Unit Application EER EnergyX System CEF Full load Rating Point Outdoor Air Temp (deg F) 28

29 ERV Load Shift Concept Without ERV 10,000 Cfm ERV 0 Ton Rooftop 100 Ton With ERV 10,000 Cfm 18 Ton 82 Ton 29

30 Efficiency Regulations (ASHRAE 90.1) ASHRAE include some requirements for energy recover, but it was limited to 75% or greater outside air and more than 5,000 supply cfm (14 tons) In the 2010 release the requirements were expanded per the following table. For ASHRAE 2013 the table will be expanded to lower % Outdoor air 30

31 Questions 31