Heat Pump Sizing Using ACCA Manual J8 It s s a Building Code Requirement Size the Equipment BEFORE You Build The bitterness of poor quality is remembered long after the sweetness of low price is forgotten!
HVAC Heating, Ventilation and Air Conditioning Provides comfort for people Allows humans to exist under adverse conditions.
WHY CARE ABOUT THE HVAC EQUIPMENT? Human Comfort Zone (After All, it s s Humans We re Experimenting With)
HEAT PUMP SIZING FSEC Study (1996 489 HVAC contractors) Rules of thumb prevail Intentionally oversize Tons per square foot (350-700) Whatever s on sale CFM per square foot Manual J (33%)
COMFORT Comfort is primary intent of HVAC systems. Productivity Building Durability Health Mold
HVAC BUZZWORDS BTU = British Thermal Unit energy to heat 1 pound of water from 39 F to 40 F 1 Ton = 12,000 BTUh Dry Bulb Temperature = air temperature Wet Bulb Temperature = temperature of adiabatic saturation psychrometer or a piece of cloth on a thermometer, temp it evaporates less than dry bulb Dew Point = Temperature were air is saturated and condensation starts Relative Humidity = Amount of water vapor in the air CFM = Cubic Feet per Minute, air volume FPM = Feet Per Minute, air velocity Pascal Pa = Pressure (1 Pa =.000145 Psi) ~ 250 Pa = 1 wc Sensible Load = reduces the temperature Latent Load = reduces the moisture Sensible Heat Ratio (SHR) = ratio between the sensible and total load Grains for moisture = indicate amount of water vapor per pound of air Manual J = method for estimating the loads Manual D = method for designing & sizing the duct work from the Manual J Psychrometrics = the measurement of the heat and water vapor properties of air Enthalpy = a measure of the total energy of a thermodynamic system
HEAT PUMPS Heat pumps remove heat from the house in the summer and dump it outside cooling season Heat pumps remove heat from the outside air in the winter and dump inside heating season Cooling Degree Days (CDD) & Heating Degree Days (HDD) typical outside base 65 F (example Avg temp for the day is 80 F 65 F= 15 CDD for one month 450 CDD North Florida Climate Zone 2 design for the cooling season
HEAT FLOW Conduction Convection Radiation
SOLAR HEAT GAIN COEFFICIENT (SHGC) The amount of solar heat energy allowed to pass through a window Example: SHGC = 0.40 Allows 40% through and turns 60% away
ENERGY EFFICIENCY LOW-E WINDOWS AND COMFORT Mean Radiant Temperature (MRT) has 40% more impact than ambient temperature 76 0 F Ambient/45% RH 70 0 F Ambient/65% RH 77 0 F 77 0 F 90 0 F 90 0 F More Comfort Less Comfort
CONTROLLING AIR FLOW: RULE #1 Where there is a driving force, Where there is a air will take the path of least resistance through largest hole. air
CONTROLLING AIR FLOW: RULE #2 Driving Forces always move in predictable directions: More Pressure More Moisture More Hot (air and moisture) Less Pressure Less Moisture Less Hot
CONTROLLING AIR FLOW: RULE #3 One Out = One In
HVAC SYSTEM DESIGN Importance of Design Undersized systems = discomfort Oversized systems = wear & tear on equipment, discomfort (cooling), unnecessary expense, higher initial cost Duct design can affect efficiency and system s ability to heat/cool evenly The RIGHT SIZED equipment is critical for performance. 95% of problems related to over sizing, duct leakage, poor duct design
OBTAIN A GOOD SYSTEM DESIGN AND INSTALLATION The HVAC equipment, duct layout, and ductwork are the heart, veins & arteries of the house. Find a contractor that will take the time to design and install it right Create specifications for contractors Ensure specifications are followed Seek out Best Value this is a cost avoidance issue - cheap doesn t work unless you want lots of call backs.
STEPS to a COMFORTABLE HOMEOWNER Manual J8 Load Analysis Manual D Duct system design & sizing Manual S Equipment selection Installation duct sealing/insulation, thermostat location Commissioning Compressor and AHU checks Ducts verify CFM/FPM and balance system
MANUAL J8 Procedure used to estimate the heat loss and gain of conventional residential structures for the purpose of HVAC sizing Determine room-by-room loads Manual J examines: Enclosure elements Air leakage System losses / gains Sun position Latent and internal gains
HEAT LOSS
HEAT GAIN
HEAT TRANSFER Resistance (R-Value) U = 1 / R Example R30 = U.033 ~ R11 = U.09 Measuring Heat Loss Q = U x A x T Q = heat flow (BTUH) U = thermal conductivity (U=1/R) A = surface area (square feet) T = temperature difference across component ( F) U-Value is the rate of heat flow in Btu/h through a one ft 2 area when one side is 1 o F warmer
HOW MANUAL J WORKS BTUH heat loss or gain through an assembly Example Q BTUH = U x A x T 500 sq. ft. of wall insulated to R-19 Interior temp at 75 and exterior at 89 U-value = 1/R value: 1/19 =.053 Delta T is the difference in temperature across a building component that governs heat loss or gain: 89-75 = 14.053 x 500 x 14 = 371 BTUH
OBJECTIVES OF MANUAL J8 LOAD CALCULATION To determine the proper sizing of HVAC equipment for a structure (Block Load) To determine the heating & cooling requirements for individual rooms ( Room by Room load) Determine Proper Duct Design Why Bother Sizing? Obviously don t want one to small Avoid Callbacks So just make it real big
HIGH PERFORMANCE HOUSES So what is the cause for concern? Improved thermal envelope leads to reduced heating and cooling loads which results in smaller HVAC equipment Used to use 400 sqft / ton as an estimation of size Now 600 and up to 1000 sqft / ton Reduced amount of airflow in the system Standard to oversize ducts result in lower velocities Lower velocities at diffusers reduce throw and mixing Impact of duct leakage is amplified
WHY USE MJ8 The heating and cooling load estimates affect every aspect of the system design procedure Type of system (variable volume/capacity) Equipment selection Placement and selection of air distribution hardware Duct routing and airway sizing or pipe layout and sizing Because of this the load calculation must be as accurate as possible
DESIGN CONDITIONS ONLY OCCUR FOR A FEW DOZEN HOURS PER SEASON
RADIANT LOADS CAN HAVE THE LARGEST IMPACT EAST Elevation WEST Elevation
WATCH the INPUTS
LOAD VS TOTAL CAPACITY The total system capacity ~ example: 3 TONS (36,000 Btuh) is required only about 3-4% 3 of the time.
MJ8 ROOM by ROOM
AIR INFILTRATION Blower Door Test Measures how much air leaks in/out of a home s envelope by studying how much air must be removed from the home to reach a certain pressure level (50 Pascal reference), thus testing the efficiency of the building envelope. Directly influences the size of the equipment because it affects the latent and sensible loads.
DUCT LEAKAGE Influences how the building reacts in terms of health, safety, durability, comfort, and energy efficiency. Can be estimated with a high degree of accuracy. Can be tested with a high degree of accuracy. Can be eliminated.
HEAT PUMP EFFICIENCY Heating Mode Measured by HSPF ENERGY STAR at HSPF 8.2 Cooling Mode Cooling efficiency measured by SEER Federal minimum SEER 13 ENERGY STAR criterion SEER 14
ENERGY EFFICIENCY EQUIPMENT RIGHT-SIZING Benefits: Lower Cost Increased Efficiency Longer Lifetime Better Moisture Control Improved Comfort Reduced Callbacks SEER 14 13 12 11 10 9 8 7
NEW CONSTRUCTION MISTAKES The Infiltration always is a guess!!! Using the wrong Infiltration rate Actually just assume leaky construction Assuming Duct & Envelope Leakage Equivalent Same plan is used for multiple subdivisions Looking at worst case scenarios Not Evaluating Overhangs & Benefits Add some for parties What s on sale All of this can lead to improper sizing of HVAC Equipment
THE SCIENCE BEHIND THE VALUE CONTROLLING AIR FLOW: INSULATION Resists Heat Flow Air Flow need Air Barrier
THE SCIENCE BEHIND THE VALUE WHY CONTROL AIR FLOW? Warm Air Gets Cold Loses Moisture Impact: All action happens at surfaces where warm air can condensate on cold surfaces. Air flow must be controlled to avoid moisture problems.
THE SCIENCE BEHIND THE VALUE WHY CONTROL AIR FLOW Without Insulation: Outside: 30 o F 34 55 o F Inside: 70 o F, 45 0 F Dew Pt. Impact: Insulated walls create cold surfaces. Insulated homes must be sealed tight to avoid moisture problems.
THE SCIENCE BEHIND THE VALUE CONTROLLING MOISTURE FLOW Hot-Humid Humid Climate: Outside: 85 o F, Inside: 70 o F Driving Force Vapor Barrier faced insulation, faced sheathing, unfaced insulation. 72 o F
ENERGY EFFICIENCY INSULATION: VALUE KILLERS Incomplete Air Barrier Misalignment with Air Barrier Gaps Voids Compression Wind Intrusion
ENERGY EFFICIENCY ALIGN AIR AND THERMAL BARRIERS Continuous Full contact with interior air barrier (e.g., sheet rock) Fully enclose conditioned space
ENERGY EFFICIENCY AIR BARRIER ALIGNMENT: BONUS ROOM Solution: align insulation add air barriers 125 o F Thermal Bypass Bonus 110 o F Room 110 o F 100 o F Garage Thermal Bypass
Solution: ENERGY EFFICIENCY AIR BARRIER ALIGNMENT: CANTILEVER align insulation add air barriers Cantilever Thermal Bypass Thermal Bypass
ENERGY EFFICIENCY TIGHT CONSTRUCTION: WHY? Eliminate unwanted heat loss/gain Eliminate potential moisture problems by avoiding humid air flow through construction assemblies Eliminate outdoor pollutants (e.g., humidity, dust, pollen)
ENERGY EFFICIENCY TIGHT CONSTRUCTION: HOW? Seal Un-designed Holes Cracks Holes Shafts Control Air Flow with Designed Holes Mechanical Ventilation Exhaust Fans Pressure Balancing
ENERGY EFFICIENCY TIGHT CONSTRUCTION: HOLES/CRACKS
ENERGY EFFICIENCY ENERGY EFFICIENT DUCTS Ducts Sized with ACCA Manual D Seal With Mastic Insulate Avoid Using Building Cavities as Ducts Get it Inside if Possible
ENERGY EFFICIENCY SEALING DUCTS: PROBLEMS
ENERGY EFFICIENCY SEALING DUCTS WITH MASTIC
Heating: ENERGY EFFICIENCY ENERGY EFFICIENT EQUIPMENT Super Efficiency: 90+ AFUE HSPF 8.2 Cooling: 14 SEER Multi-Speed Air Handler: Variable Speed Blower Motor Air-Tight Cabinet
SUMMARY ENERGY EFFICIENCY PERFORMANCE ADVANTAGE Unless you re prepared to break the laws of physics, energy efficiency delivers: Lower Utility Costs More Comfort More Durability Improved Indoor Air Quality Environmental Protection Less call backs Happy Homeowner more sales
FOR MORE INFORMATION Visit us on the Web: http://www.usahers.com Or call Tim @ 904-571-9955 Henry @ 904-233-7299