Why Doesn t My HVAC System Work?

Transcription

1 Why Doesn t My HVAC System y y y Work?

2 Defining Not Working Too hot and humid in the Summer-- Maybe the whole house, or just certain rooms.

3 Too cold in the Winter Goldilocks and the three bears problem-- Some rooms too hot, Some rooms to cold, No room just right.

4 Cold and Sweaty in the Summer Cold and sweaty! Low air temperature And high indoor relative humidity

5 Too Expensive to Operate--$$$$ Comfort is a part of the Energy Efficiency Equation.

6 Give me Shelter.. Comfort Mick ain t singing give me shelter any more. He, and everybody else, demands year around comfort.

7 Making the HVAC work Insure that house is built right Insulation installed so that it works House is tight Appropriate windows are chosen Size the system right Size the system right Room by Room Manual J Use the Manual S (selection process)

8 Making HVAC system work (continued) Install right, Correct airflow Correct charge Correct gas pressure

9 Making the HVAC system work Keep the conditioned air hot or cool Ducts inside Airtight, well insulated, minimize surface area Delivering and returning the correct airflow to each zone Manual J and Manual D Mix the Air Register and Grille Selection

10 What is comfort?

11 Thermal Comfort is that condition of mind in which satisfaction is expressed with the thermal environment ASHRAE Handbook 2001 ASHRAE Handbook of Fundamentals

12 Thermal Comfort is determined by many factors Comfort is a factor of: air temperature relative humidity air speed surface temperature occupant activity occupant clothing

13 Mean Radiant Temperature Cold surfaces produce down drafts. Cold surfaces decrease comfort due to a lower mean radiant temperature.

14 The Limits of Comfort

15 EQUIPMENT SIZING

16 One Size Does Not Fit All!

17 Bigger is Not Always Better!

18 What is a Ton of Coolth? Ton of Refrigeration: one ton of ice melted over a 24 hr. period would absorb 288,000 BTUs of heat. The latent heat of melting ice is 144 Btu/lb. Thus 2000 lb x 144 Btu/lb= 288,000 BTU/24 hr. Refrigeration equipment is rated by its ability to remove heat per hour: 288,000 Btu/24 hr x 24hr/day = 12,000 Btu/hr. 1 ton =12,000 BTU/hr. The goal of sizing is to deliver the ice at the right time in the right amount.

19 Over Sizing = Lower Efficiency

20 Right Sizing Benefits Greater Comfort Better air mixing Less thermal stratification Fewer cold spots Lower sound levels Lower initial costs Better efficiency Longer equipment life

21 Manual J is one of Several ACCA Manuals Manual J is for heat loss and heat gain Manual S is for equipment selection Manual D is for duct design Manual H is for heat pumps Manual T is for register and grille selection

22 The Facts on Manual J Created and supported by ACCA (a contractors association) Typically oversizes by 15% to 20% (no need to add your own bump) Field tested

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25 What Goes into a Manual J Load Calculation? Conduction heat gain or loss through building surfaces Radiation from the sun (windows) Heat and moisture given off by equipment and appliances Heat and moisture given off by people Heat and moisture gained or lost by infiltration Heat gain or duct loss through duct system (if in attic) THE SIZE OF THE HEATING SYSTEM IS EQUAL TO THE PEAK HEAT LOSS THE SIZE OF THE AC UNIT IS EQUAL TO THE PEAK THE SIZE OF THE AC UNIT IS EQUAL TO THE PEAK HEAT GAIN

26 Manual J is Like a Cheap Stereo Tweak some knobs, and a lot happens Crank other knobs, and not much happens This class will focus on the knobs that make things happen

27 The knobs that really matter once the house is insulated-- Windows Duct gains and losses (especially in hot and bothered climates) Air exchange (especially in hot and bothered climates) Picking the right weather station

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31 Once a house has insulation, its size has a small impact on sizing-- Boise 1000 sq ft attic Corpus Christi 1000 sq ft attic Boise 3000 sq ft attic Corpus Christi 3000 sq ft attic Boise Difference Corpus Christi Difference Sensible Load 1,407 1,500 4,221 4,500 2,814 3,000 Total Load 1,407 1,500 4,221 4,500 2,814 3,000

32 R 49 Attic SQ Ft of Building Surface Required to Create 1 Ton of Cooling Load h U=.35 SHGC =.33 E&W SP window E&W U=.65 SHGC =.65 E&W U=.65 SHGC =.40 E&W U=.35 SHGC =.33 South SP window South U=.65 SHGC =.65 South U=.65 SHGC =.40 South U=.35 SHGC =.33 R 0 wall R 11 wall R 19 wall R 11 attic R 19 attic R 38 Attic SLC SQ Ft To Create 1 Ton of Gain Corpus Christi SQ Ft To Create 1 Ton of Gain North SP window th U=.65 SHGC =.65 North U=.65 SHGC =.40 Norh North

33 Manual J Cooling Assumptions 1. Glass area is 10% to 25% of the floor area 2. Solar gains and transmission loads are averaged. Not peak loads. All rooms do not peak simultaneously. 3. No provision for unusual loads (hot tubs)

34 The Big Mistakes Using wrong window data Using wrong duct multiplier Using incorrect ACH (air leakage) Using the results from Manual J to directly size heating and cooling equipment Failing to use or understand HVAC manufacturers tables

35 Manual J Short-Cut Lingo: Windows HTMs cooling : glass Based on the average heat gain through glass that t occurs in the warmest month over an hourly period that extends from mid-morning through late afternoon. Includes: conduction gain radiation gain

36 Getting Windows Right Windows dominate the cooling load in low humidity zones; Accurately describing the windows is critical to obtaining the correct cooling load.

37 Low SHGC = Lower Heat Gain

38 NFRC LABEL

39 Difference in BTU Gain Between Windows with 0.35 SHGC vs SHGC Orienta- tion Sq footage Boise SHGC=.35 Corpus Christi SHGC=.35 Boise SHGC=.65 Corpus Christi SHGC=.65 Boise Differ- ence Corpus Christi Difference North ,000 1, East & West 180 6,804 6,874 13,264 13,406 6,460 6,532 South 60 1, ,386 1,699 1, Total 280 8,561 8,295 16,649 16,132 8,088 7,836

40 Duct Loss Multipliers li This is a big knob! Can be applied on a room by room basis Duct runs inside vs. duct runs outside the envelope The envelope is both the thermal barrier and the air barrier If ducts are outside, the best we can do is 20% The worst is huge--50% to 70% Average between 25% to 45% Manual J (Version 8) has high duct gains even when insulated and extremely tight Well-insulated l duct systems with leakage at less than 5% of conditioned floor area have a 20-25% duct loss multiplier

41 Duct Loss Multipliers A 25% duct gain on a house with 30,000 BTU/hr of peak gain would add another 7,500 Btu/hr of sensible gain Leaky ducts in hot humid climates add to the latent load and the sensible load Leaky return ducts in hot and dry climates lower the latent load

42 Duct loss is both leakage and g conduction

43 Design ACH Should use a separate winter and summer ACH Manual J will let you use blower door data (good option) Manual J will let you try a prescriptive approach (worst option) Manual J will let you enter your own educated input (best option)

44 Total Cooling Load: Sensible and dlatent Sensible cooling load. That part of the cooling load that involves lowering the dry bulb temperature. Latent cooling load. That part of the cooling load the involves removing water vapor from the air (dehumidification). In most of the West, almost all the cooling load is sensible.

45 Psychrometric Definitions Wet Bulb Temperature The wet bulb temperature is measured with a wetted thermometer in rapidly moving air

46 Infiltration Loads 0.35 ACH vs. 1 ACH Boise =.35 Corpus Christi =.35 Boise ACH =1 Corpus Christi ACH=1 Boise Difference Corpus Christi Difference Latent Load 0 4, , ,014 Sensible Load ,110 2,375 6,029 6,773 3,919 4,398 Total Load 2,110 6,690 6,029 19,102 3,919 12,412

47 Manual S: Cooling Equipment Tables: What they tell you for a given set of conditions-- o Total Capacity BTUH Sensible Capacity BTUH Latent Capacity BTUH

48 Manual S Equipment Tables--What you need to know-- Outside dry bulb Entering (return) wet bulb Entering dry bulb CFM of fan (at real operating pressures)

49 Remember! The capacity of the air conditioner is not the same as the load calculated by Manual J You must match the load of the house at design conditions to the capacity of the AC unit at design conditions

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51 AC Capacity Rating Table

52 Manual J and Manual S Proctor Engineering has proven that in the field, Manual J-- Over-estimates cooling loads by about 20% to 25%. The process really works. Don t add your own bump.

53 Low Air Flow Per Ton Without the correct airflow, a 13 SEER 3 ton air conditioner might be an 8 SEER 2 ton Air conditioner. Studies repeat show that 60% to 85% of all AC systems have less than adequate airflow

54 Low Air Flow = Decrease in Capacity CFM/TON Percent of Ideal Air Flow Percent Deviation from Ideal Air Flow AC Capacity Reduction of Capacity % 100% 48, % 11% 44,640-3, % 22% 43,200-4, % 33% 41,760-6,240 Off the chart 55% 44% 38,400-9,600

55 Low Air Flow = Decrease in Efficiency AC Efficiency vs. Air Flow Full Cap pacity (F Fraction of Rating at Air Flow Deviation From Full Air Flow

56 Impact of Installation Factors on RFA] Field Adjuste ed SEER [SEE Field Ad Adjusted SEER [SE SEERFA] Central A/C and Typical linstallation 6 Typical Installation Rated SEER Rated 12 SEER Rated SEER Courtesy of Advanced Energy

57 Many Causes of flow Airflow

58 Courtesy of Advanced Energy

59 Courtesy of Advanced Energy

60 Courtesy of Advanced Energy

61 Courtesy of Courtesy of Advanced Energy

62 Courtesy of Advanced Energy

63 Courtesy of Advanced Energy

64 The Kinked Hose Syndrome

65 Why do we hang ducts in attics?

66 Sizing i Duct Work Sizing duct work Bigger means less restriction, ti more airflow Too big to individual rooms means not enough mixing power

67 What Creates Resistance? Friction of air moving through ducts The faster the air is moving (velocity), the greater the friction Devices (ACCA s words for objects placed in the air stream) including: Evaporator coils Filters Registers and grilles

68 External Static Pressure Typical Fan Curve ESP CFM

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72 Undersized Returns System should operate quietly (Fast air = noise)

73 Sizing Returns A general rule is one net square foot of return grille per ton-- A 20 x 20 inch grill = 400 sq. in. 400 x.75 = 300 sq. in. NFA 300 sq. in. / 144 sq. in. = 2.08 sq. ft. Just enough for a two ton system. Returns can not be oversized.

74 Quick Rules for Duct Sizing For every 1,000 Btus of furnace input there should be 2 sq. inches of duct on both the return and the supply side Example: 60,000 Btu input furnace would need 120 sq. inches of return and supply

75 Quick Rules for Gas Furnaces With Air Conditioner Coil Added An ideal situation to maximize the performance of the AC unit is to have 6 sq. inches of duct on the supply side and return side for every 1,000 Btus of air conditioning Example: A 2 ton AC (24,000 Btus) would need 144 sq. inches of return p (, ) q and supply duct

76 The Rules Applied

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78 Return and Return Grille Sizing AC SIZE CFM Minimum Size Square Minimum Square Grille Minimum Rough Sq in Tons Sheet Metal Inches Flex Duct Inches Size (NFA) Inches NFA , , , , , ,

79 Where is my 3 ton fan? 40K BTU 2 Ton 60K BTU 3 Ton 80 K BTU 3.5 Ton 100 K BTU 4 Ton 120K BTU 5 Ton

80 ECMs to the Rescue? CFM VS Static Pressure (CFM) Airflow( PSC ECM Static Pressure (IW)

81 ECMs are not magic Watts VS Static Pressure Wa tts PSC ECM Static Pressure

82 Why Duct Sealing is Important Heating Efficiencies Homes with Furnace and All Ducts Exterior Base Sample System Efficiency Homes with Furnace and All Ducts Interior Inside Vs Outside Greater effect on efficiency i than 10 to 13 SEER or 80 to 90% AFUE

83 Ducts on the Inside Getting ducts on the inside of the conditioned space is best-- But if you can t: Seal them air tight Maximize the R-value Keep them as short as possible

84 Ducts on the Inside Inside ducts don t always look like this but the effect is the same. Duct losses are regained by the house.

85 Ducts on the inside

86 Ducts Outside the House are Energy Wasters Attics and ventilated crawl spaces with insulated floors, are outside. Centre Georges Pompidou in Paris, France -- Air conditioning ducts are blue, water pipes are green and electricity lines are yellow. Escalators are red. White ducts are ventilation shafts for the underground areas.

87 Four Keys to Tighter Ducts Plug don t Paint--Mastic should be about the thickness of a nickel to seal properly Pre-mastic as many yparts as possible Use parts that don t leak (when possible) Test!

88 Mastic Used, But Still a Leak

89 Ducts Must Be Permanently Tight Pay attention to gores This Means: Tape can cover poor workmanship, mastic can t Sealed with Mastic Tape is neither a fastener nor a permanent sealant.

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91 The Duct Leakage Test Testing is an integral part of installing tight ducts

92 Heat Pump Control Requirements (auxiliary heat) Install outdoor thermostat or equivalent control and set at 35 F Note this means using a balance point of 30º F or lower is critical

93 Advanced Heat Pump Controls

94 Rt Return Air or Return Rt Error? Impact upon infiltration of closing interior doors with unit running ur Air C hang es/ho Doors open Doors closed Two doors closed FAN ON Four doors closed All doors closed

95 Transfer Duct for Reduction of Pressure and Transfer Duct for Reduction of Pressure and Free Flow of Heated and Air Conditioned Air

96 Creating Return Paths for Balanced Flow and Pressure Sizing transfer grilles and ducts.75 sq. in. Rough opening between the room and the main body of the house for every cfm delivered to the room Design the duct at.03 WC, with a velocity of 350 to 400 FPM

97 ACH: Forced air interactions Leaky ducts are a major driver of infiltration Homes with single zone returns have significantly larger ACHs when the doors are closed Leaky ducts and closed doors are real losers

98 Fan Flow Measurement is with Flow Plate Recommended CFM/Ton is 400 to 450/ton

99 Correct Refrigerant Charge Sub-cooling: The removal of sensible heat from a liquid after the refrigerant has changed into liquid. id This takes place in the condenser. Superheat: The addition of sensible heat to a refrigerant after it has changed to 100% vapor. This takes place in the evaporator.

100 Performance testing of heat pumps and AC units Refrigeration units must have their charge checked by using superheat or sub cool measurements.

101 The problem, more house, less load, same fan, less mixing Courtesy of Ibacos

102 Courtesy of Ibacos

103 Performance of Various Supply Registers Courtesy of Ibacos

104 Air mixing in a zone Pi Primary air induces or set in motion the air surrounding it Secondary air is 10 to 20 times the volume of the primary air Hence 80 cfm of primary air sets 800 to 1600 cfm of secondary air into motion

105 Register Throw Throw is the distance the air travels before it reaches some specific value (usually 50 feet per minute).

106 Spread refers to how wide the jet of primary becomes Spread decreases as throw increases Register Spread

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108 Courtesy of Ibacos

109 High efficiency gas fireplaces and stoves No ducts! Zone Control Radiant Heat source Plus convective heat source AFUE of 80%

110 Ductless Mini Split Heat Pump Most of the???? does not move air, they move refrigerant

111 Ductless Heat Pumps No ducts! Zone Control Inverter technology allows heat pump to maintain capacity down to 0 F Moves refrigerant, not air One outdoor unit can serve multiple indoor units

112 This is a supply outlet

113 Can you find the heat pump?

114 Engineered Size Vs. Installed Size Installed Vs actual tonnage TEST!! The Disappearing Ton Cooling Capacity loss in BTUs in Boise Idaho with two ton 10SEER unit Cooling load of house 16,900 Difference Full capacity 19,600 2,700 12% low flow ,720 20% undercharged ,935 30% duct Loss ,125 All refrigerant based heating and cooling systems must be tested to assure capacity and efficiency. Without testing, a four ton might be a two ton. Added load from duct induced infiltration ,225

115 The Comfort Recipe Equipment sizing i (the baby b bear every time) Duct sizing (delivering the right amount of air to each room) Duct installation (keeping the just paid for conditioned air in the house) Installation (making sure the system operates at the efficiency and capacity that it is designed for) Making sure the insulation company did their job Mixing the air within the conditioned zone