HVAC Energy Flow in Buildings Charles H. Culp, P.E., Ph.D., FASHRAE, - - PowerPoint PPT Presentation

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HVAC Energy Flow in Buildings Charles H. Culp, P.E., Ph.D., FASHRAE, - - PowerPoint PPT Presentation

Sep 04, 2022 15 likes •455 views

HVAC Energy Flow in Buildings Charles H. Culp, P.E., Ph.D., FASHRAE, LEED-AP Professor, Department of Architecture Associate Director, Energy Systems Lab Texas A&M University Goals View a buildings energy flow Differences

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SLIDE 1

HVAC Energy Flow in Buildings

Charles H. Culp, P.E., Ph.D., FASHRAE, LEED-AP

Professor, Department of Architecture Associate Director, Energy Systems Lab

Texas A&M University

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SLIDE 2

Goals

  • View a building’s energy flow
  • Differences between commercial and residential buildings
  • Building HVAC equipment
  • Comfort considerations
  • Health considerations
  • Limits of building efficiency
  • Advances in new buildings
  • Advances in improving existing buildings
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SLIDE 3

Conduction

Convection Evaporation if wet Radiation Infiltration Ground Conduction Exfiltration and Exhaust Solar

QClimateSensitive = QSolar + QWeather + QOutsideAir+ QGround The Climate Sensitive load is the sum of:

AC

Weather Temperature RH … Outside Air Ventilation

Building Energy Flow

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SLIDE 4

Conduction

Convection Evaporation if wet Infiltration Ground Conduction Exfiltration and Exhaust

QInternal = QPeople + QLights + QPlug The Internal load is the sum of:

Solar

AC

Weather Temperature RH … Outside Air Ventilation

Building Energy Flow

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SLIDE 5

Conduction

Convection Evaporation if wet Infiltration Ground Conduction Exfiltration and Exhaust

QTotal = QClimateSensitive + QInternal The Total load is the sum of:

Solar

AC

Weather Temperature RH … Outside Air Ventilation

Building Energy Flow

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SLIDE 6

Conduction

Convection Evaporation if wet Infiltration Ground Conduction Exfiltration and Exhaust

QTotal = QClimateSensitive + QInternal The Total load is the sum of:

Solar Weather Temperature RH … Outside Air Ventilation

Building Energy Flow

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SLIDE 7

Conduction Convection Evaporation if wet Radiation Ground Conduction Exhale / Inhale Solar

The Climate Sensitive heat load is the sum of: QClimateSensitive = QSolar + QWeather + QOutsideAir+ QGround

Weather Temperature RH … Outside Air Ventilation

Personal Energy Flow

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SLIDE 8

Conduction Convection Evaporation if wet Radiation Ground Conduction Exhale / Inhale Solar

The Internal heat load is the sum of: QInternal = QSensible + QLatent

Sensible Latent

Weather Temperature RH …

Personal Energy Flow

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SLIDE 9

Conduction Convection Evaporation if wet Radiation Ground Conduction Exhale / Inhale Solar

The Total heat load is the sum of:

Sensible Latent

QTotal = QClimateSensitive + QInternal

Personal Energy Flow

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SLIDE 10

Heat Flow

  • HVAC changes heat flows
  • Move heat to outside in summer

Outdoor Unit

basc.pnnl.gov

Heat Pump – Summer Cooling

Indoor Unit Suction Line Liquid Line

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SLIDE 11

Heat Flow

  • HVAC changes heat flows
  • Move cold to outside in winter

Outdoor Unit

basc.pnnl.gov

Heat Pump – Winter Heating

Indoor Unit Suction Line Liquid Line

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SLIDE 12
  • A Residential Systems Contains
  • Recycles indoor air (where does fresh air come from?)
  • Cooling
  • Compressor
  • Evaporator
  • Condenser
  • Expansion device
  • Fan
  • Ducts and registers
  • Filter(s)
  • Heating
  • Above +
  • Burner
  • Heat exchanger

HVAC - Residential

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SLIDE 13

Psychrometric Chart

  • Variables of Interest
  • Temperature
  • Impacts comfort
  • Influences condensation
  • Relative Humidity
  • Can calculate dew point from relative humidity/temperature
  • Want inside temperature higher than dew point of outside air
  • Humidity Ratio
  • Ratio of lbs of H2O to lbs of dry air
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SLIDE 14

Temperature 40 50 60 70 80 90 100 110 ºF

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SLIDE 15

Relative Humidity 40% 20% 60% 80% 100% 50%

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SLIDE 16

Humidity Ratio 0.009 0.006 0.003 0.018 0.015 0.012 0.027 0.024 0.021

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SLIDE 17

Temperature Humidity Ratio Relative Humidity 0.009 0.006 0.003 0.018 0.015 0.012 0.027 0.024 0.021 40 20 60 80 100 50 40 50 60 70 80 90 100 110 ºF

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SLIDE 18

Health Indoors - Residential

  • Asthma
  • Incidence1,2
  • 2008 – 2.8%
  • 1996 – 0.6%
  • 1980 – 0.25%
  • Other refs indicate growth from 2% of the population to

10.6%.

  • Costs2
  • About $3,300 per person per year

1Asthma incidence: data from the Nat. Health Interview Survey,

http://www.ncbi.nlm.nih.gov/pubmed/17365207

2American Academy of Allergy Asthma and Immunology,

http://www.aaaai.org/about-the-aaaai/newsroom/asthma-statistics.aspx

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SLIDE 19

Health Indoors - Residential

SA (Supply Air) IA (Inside Air)

C C

Filter

Attic ducts leak Negative pressure inside Inside 75°F 50% RH Summer 95°F 59% RH ~78°F Dew Point

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SLIDE 20

Health Indoors - Residential

Summer 95°F 59% RH ~78°F Dew Point

SA (Supply Air) IA (Inside Air)

C C

Filter

Attic ducts leak Negative pressure inside Inside 75°F 50% RH 95°F 85°F 78°F

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SLIDE 21

Health Indoors - Residential

  • Negative Pressure
  • Positive Pressure

Inside 75°F Inside 75°F Outside 95°F 59% RH Outside 95°F 59% RH Inside 75°F 50% RH 85°F 85°F Inside 75°F 50% RH

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SLIDE 22

Bad

Inside 75°F Inside 75°F 50% RH 85°F Outside 95°F 50% RH 95°F

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SLIDE 23

Good

Inside 75°F Outside 95°F 50% RH 85°F Inside 75°F 50% RH

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SLIDE 24

Health Indoors - Residential

SA (Supply Air) IA (Inside Air)

C C

Filter

Attic ducts leak Adjustable pressure inside Inside 75°F 50% RH Summer 95°F 59% RH ~78°F Dew Point

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SLIDE 25

Health Indoors - Commercial

  • Generally positively pressurized
  • Maintenance is an issue

AHU – Air Handler Unit

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SLIDE 26

ASHRAE Standard 90.1-2013

  • For commercial buildings
  • Specifies efficiency

requirements for:

  • Insulation
  • HVAC
  • Lighting
  • Power
  • Title: Thermal Environmental Conditions for

Human Occupancy

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SLIDE 27

ASHRAE Standard 62.1-2013

  • For commercial buildings
  • Specifies minimum outside

air

  • Ventilation Rate Procedure
  • People contamination
  • Building materials

contamination

  • OA is the Outside Air

required

  • Title: Ventilation and Acceptable Indoor Air

Quality in Low-Rise Residential Buildings

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SLIDE 28

ASHRAE Standard 62.1-2013

  • For commercial buildings
  • Specifies minimum outside

air

  • Title: Ventilation and Acceptable Indoor Air

Quality in Low-Rise Residential Buildings

#

  • 2

2

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SLIDE 29

ASHRAE Standard 55-2013

  • Title: Thermal Environmental Conditions for

Human Occupancy

  • Specifies commercial

building comfort requirements

  • Provides an evaluation

procedure for existing buildings

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SLIDE 30

Personal Comfort

  • Balance temperature / moisture
  • Keep body core temperature at a comfortable level
  • Sedentary comfort
  • Sensible: ~250 Btu/hr
  • Latent: ~200 Btu/hr
  • Active comfort
  • Sensible: Ranges from 300 to 800+ Btu/hr
  • Latent: ~250 to 700+ Btu/hr
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SLIDE 31

Personal Comfort

  • From “Thermal Comfort under Transient

Metabolic and Dynamic Localized Airflow Conditions”

  • A. Ugursal, PhD Thesis
  • Background
  • Occupant productivity

Seppanen et al. (2004)

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SLIDE 32

Personal Comfort

  • Three groups of body parts based on

contribution to overall thermal sensation1:

  • Highest:

back, chest, pelvis

  • Moderately: face, neck, breathing, head, arms, legs
  • Least:

hands, feet

  • Measurements

1Zhang (2003)

1: Forehead 2: Cheek 3: Neck 4: Chest 5: Abdomen 6: Upper Back 7: Lower Back 8: Upper Arm 9: Lower Arm 10: Hand 11: Anterior Thigh 12: Anterio-medial Thigh 13: Anterior Calf 14: Posterior Calf 15: Instep

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SLIDE 33

Personal Comfort

  • Results
  • People demand more air even when they feel cool
  • Pulsed air increased perception of thermal comfort
  • Draught rating of our test (5%) was significantly lower than the

Standard 55 prediction (16%) Experimental Chamber

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SLIDE 34

Limits of Building Efficiency

  • Study done by Claridge and Tanskyi at the ESL
  • Assumptions
  • Comply with ASHRAE energy efficiency, comfort and

ventilation standards

  • Calibrated building energy use to actual use

ESL Building – 25 kft2 Bullitt Cascadia Center – 52 kft2

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SLIDE 35

Limits of Building Efficiency

  • Use – kBtu/ft2-yr
  • Normal Building:

82 kBtu/ft2-yr

  • ESL Building:

50 kBtu/ft2-yr

  • Bullitt Cascadia Center: 16 kBtu/ft2-yr (planned)
  • “Carnot Limit” Building:

0.73 kBtu/ft2-yr ESL Building – 25 kft2 Bullitt Cascadia Center – 52 kft2

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SLIDE 36

Limits of Building Efficiency

  • Demand – kBtu/ft2-yr
  • ESL Building:

138 kW summer 178 kW winter

  • “Carnot Limit” Building: 2.2 kW summer

1.6 kW winter ESL Building – 25 kft2

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SLIDE 37

Improving Residential

  • Today’s residential buildings
  • Get outside air through envelope leakage
  • Stick built, poor sealing
  • Lack control
  • Typically control on/off to temperature only
  • Tomorrow’s residential buildings
  • Tighter and better insulated
  • Sprayed foam is becoming more common
  • Still 2-times the cost of fiberglass
  • Tightness REQUIRES outside air be provided
  • Higher performance HVAC
  • Enthalpy recovery ventilators (ERVs, HRVs) available
  • New very-high efficiency AC in the lab today
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SLIDE 38

Improving Residential

  • Enthalpy recovery ventilators (ERVs, HRVs)

available

  • Existing commercial HRVs deliver 69% or so

effectiveness

  • HRV in lab delivers 90% effectiveness, ~85%

efficiency

Straight Airfoils Airfoils Available Channel Hgt. 0.25” 0.4” 0.5”

  • Effectiveness

91% ±5% 95% ±5% 81% ±5% 69% ±5% ∆P (in-H2O) 0.16 ±0.01 0.11 ±0.01 0.09 ±.01 0.40 ±.01

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SLIDE 39

Improving Residential - Summer

  • Application of HRVs – 90% Effective
  • At 90% effectiveness
  • At 69% effectiveness

Fresh air to space Stale air to outside Outside air Exhaust air

Stale Air Out Outside Air Fresh Air Exhaust Air Winter 72°F 42°F 69°F 45°F Summer 78°F 98°F 80°F 96°F Stale Air Out Outside Air Fresh Air Exhaust Air Winter 72°F 42°F 63°F 51°F Summer 78°F 98°F 84°F 92°F

78°F 96°F

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SLIDE 40

Improving Residential - Winter

  • Application of HRVs – 90% Effective
  • At 90% effectiveness
  • At 69% effectiveness

Fresh air to space Stale air to outside Outside air Exhaust air

Stale Air Out Outside Air Fresh Air Exhaust Air Winter 72°F 42°F 69°F 45°F Summer 78°F 98°F 80°F 96°F Stale Air Out Outside Air Fresh Air Exhaust Air Winter 72°F 42°F 63°F 51°F Summer 78°F 98°F 84°F 92°F

72°F 45°F

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SLIDE 41

Improving Residential

  • Higher performance HVAC – ARPA-E, Navy
  • New very-high efficiency AC in the lab today
  • Benefits
  • Theoretical 60+ SEER with 40+ practical
  • No refrigerants
  • Generates clean H2O
  • Healthier
  • Also works with commercial buildings
  • Lab unit is working

Type System COP First Cost 3 Ton Unit Comfort Operating Cost Refrigerant ~ 3 to 5 $5K to $8K Med High Desiccant ~ 4 to 5 $7K to $14K High Very High Membrane- Evaporative ~ 5 to 18 Initial: $9K to $16K Mature: $4K to 8K High Low

Technology

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SLIDE 42

Improving Commercial

  • Today’s commercial buildings
  • Typically built to minimum standards
  • Energy use ranges 40 to 120 kBtu/ft2-yr
  • Poorly trained operators
  • Tomorrow’s commercial buildings
  • Codes are increasingly stringent
  • Will drive better materials, less “all-glass”
  • Higher performance HVAC
  • Enthalpy recovery ventilators (ERVs, HRVs) will be required
  • Several HVAC improvements moving to marketplace
  • Energy and enthalpy wheels, refrigerant compressors,

variable flow refrigerant systems, etc.

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SLIDE 43

Improving Commercial

  • Major opportunity in new and existing

buildings – Controls and Tuning

  • Existing building commissioning can achieve
  • 10% to 20% reduction in total energy use
  • Translates to a 20% to 40% reduction in HVAC energy use
  • 2 to 3 year payback
  • Healthier building since the controls will work correctly
  • $400,000
  • $200,000

$0 $200,000 $400,000 $600,000 $800,000 $1,000,000

Nov-08 Feb-09 May-09 Aug-09 Nov-09 Feb-10 May-10 Aug-10 Nov-10 Feb-11 May-11 Aug-11 Nov-11 Feb-12 Project Timeline

Net Cumulative Savings Cumulative Savings Cumulative Costs

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SLIDE 44

Summary

  • Residential buildings
  • Need to bring in outside air
  • Commercial buildings
  • Need to be operated well
  • Improve implementation of controls
  • Understand
  • Temperature
  • Moisture
  • Pressurization