Whyyy y Doesn’t My HVAC System...

Why Doesn’t My HVAC System y y yWork?

Defining “Not Working”Defining Not Working

Too hot and humid in the SummerToo hot and humid in the Summer--Maybe the whole house orwhole house, or just certain roomsrooms.

Too cold in the Winter

Goldilocks and the three b blbears problem--

S t h tSome rooms too hot,Some rooms to cold,N “j t i ht”No room “just right”.

Cold and Sweaty in the SummerCold and sweaty!Low air temperatureAnd high indoor relative humidity

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

Give me Shelter.. ComfortMick ain’t singing “give me shelter” any more.

He, and everybody else demands yearelse, demands year around comfort.

Making the HVAC workInsure that house is built rightInsure that house is built right

Insulation installed so that it worksHouse is tight Appropriate windows are chosen

Size the system rightSize the system rightRoom by Room Manual JUse the Manual S (selection process)

Making HVAC system work g y(continued)

Install right, Correct airflowCorrect airflowCorrect chargeCorrect gas pressure

Making the HVAC system workg y

Keep the conditioned air hot or cool Ducts insideAirtight, well insulated, minimize surface area

Delivering and returning the correct airflow to each g gzone

Manual J and Manual D

Mix the AirRegister and Grille Selection

What is comfort?

Thermal ComfortThermal Comfort

“…is that condition of mind in whichsatisfaction is expressed with the thermalsatisfaction is expressed with the thermalenvironment.”

--2001 ASHRAE Handbook2001 ASHRAE Handbook of Fundamentals

Thermal Comfort is determined byThermal Comfort is determined by many factors

Comfort is a factor of:air temperaturerelative humidityrelative humidityair speedsurface temperatureoccupant activityoccupant clothing

Mean Radiant TemperatureCold surfaces produce down draftsdrafts.Cold surfaces decreasedecrease comfort due to a lower mean radiant temperature.

The Limits of Comfort

EQUIPMENT SIZING

One Size Does Not Fit All!

Bigger is Not Always Better!

Wh i T f “C l h”?What is a Ton of “Coolth”?T f R f i ti t f i lt d 24 h i dTon 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 t 12 000 BTU/h1 ton =12,000 BTU/hr.

The goal of sizing is to deliver the “ice” at the right time in the right amountright amount.

Over Sizing = Lower Efficiency

Right Sizing BenefitsGreater Comfort

Better air mixingLess thermal stratificationFewer cold spotsLower sound levels

Lower initial costsBetter efficiencyLonger equipment lifeg q p

Manual J is one of Several ACCA Manuals

Manual J is for heat loss and heat gainM l S i fManual S is for equipment selectionManual D is for duct d idesignManual H is for heat pumpsManual T is for register and grille selection

Th F M l JThe Facts on Manual J

Created and supported by ACCA(a contractors’ association)(a contractors association)Typically oversizes by 15% to 20% (no need to add your own bump)(no need to add your own bump)Field tested

What Goes into a Manual J Load W at Goes to a a ua J oadCalculation?

Conduction heat gain or loss through building surfacesConduction heat gain or loss through building surfacesRadiation from the sun (windows)Heat and moisture given off by equipment and appliancesHeat and moisture given off by peopleHeat and moisture given off by peopleHeat and moisture gained or lost by infiltrationHeat 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 PEAKTHE SIZE OF THE AC UNIT IS EQUAL TO THE PEAK HEAT GAIN

Manual J is Like a Cheap Stereo…Tweak some knobs, and a lot happens

Crank other knobs, and not much happensnot much happens

This class will focus onThis class will focus on the knobs that make things happeng pp

The knobs that really matter once the yhouse is insulated--

WindowsDuct gains and losses (especially in hot and bothered climates)Air exchange (especially in hot and g ( p ybothered climates)Picking the right weather stationPicking the right weather station

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 Differenceq

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

SQ Ft f B ildi S f R i d t C t 1 T f C li L dSQ Ft of Building Surface Required to Create 1 Ton of Cooling Load

13000140001500016000

900010000110001200013000

40005000600070008000

01000200030004000

North S

P w indow

thU=.65

SHGC =.65

thU=.65

SHGC =.40

h U=.35 SHGC =.33E&W SP w indow

WU=.65

SHGC =.65

WU=.65

SHGC =.40

WU=.35

SHGC =.33

South SP w indow

thU=.65

SHGC =.65

thU=.65

SHGC =.40

thU=.35

SHGC =.33 R 0 wallR 11 w

allR 19 w

allR 11 a

t ticR 19 a

t ticR 38 A

tticR 49 A

ttic

North

North

Norh

E&W E&W E&W

South

South

South

SLC SQ Ft To Create 1 Ton of Gain Corpus Christi SQ Ft To Create 1 Ton of Gain

Manual J Cooling Assumptions1. Glass area is 10% to 25% of

the floor area2. Solar gains and transmission

loads are averaged. Not peak loads. All rooms do not peak simultaneously.

3. No provision for unusual loads (hot tubs)

The Big MistakesThe Big Mistakes

Using wrong window data Using wrong duct multiplier Using incorrect ACH (air leakage) Using the results from Manual J to directlyUsing the results from Manual J to directly size heating and cooling equipmentFailing to use or understand HVACFailing to use or understand HVAC manufacturers’ tables

Manual J Short-Cut Lingo: gWindows

HTMs cooling : glassBased on the average heat gain through glass th t i th t th h lthat occurs in the warmest month over an hourly period that extends from mid-morning through late afternoon.late afternoon.

Includes:conduction gainconduction gainradiation gain

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

Low SHGC = Lower Heat Gain

NFRC LABEL

Difference in BTU Gain Between Windows with 0.35 SHGC vs. 0.65 SHGC

Orienta-tion

Sqfootage

Boise SHGC=

35

Corpus Christi SHGC=

35

Boise SHGC=

65

Corpus Christi SHGC=

65

Boise Differ-ence

Corpus Christi

Differencetion footage .35 .35 .65 .65 ence Difference

North 40 523 536 1,000 1,026 477 490East & West 180 6,804 6,874 13,264 13,406 6,460 6,532

South 60 1,234 886 2,386 1,699 1,151 814

Total 280 8,561 8,295 16,649 16,132 8,088 7,836

D t L M lti liDuct Loss MultipliersThis is a big knob!This is a big knob!Can be applied on a room by room basis

Duct runs inside vs. duct runs outside the envelopeThe envelope is both the thermal barrier and the air barrierThe envelope is both the thermal barrier and the air barrierIf ducts are outside, the best we can do is 20%The worst is huge--50% to 70%Average between 25% to 45%g

Manual J (Version 8) has high duct gains even when insulated and extremely tightW ll i l t d d t t ith l k t l th 5% fWell-insulated duct systems with leakage at less than 5% of conditioned floor area have a 20-25% duct loss multiplier

Duct Loss MultipliersA 25% duct gain on a house with 30,000 BTU/hr of peak gain would add another 7,500 Btu/hr of sensible gainLeaky ducts in hot humid climates add to the ylatent load and the sensible loadLeaky return ducts in hot and dry climates y ylower the latent load

Duct loss is both leakage and gconduction

Design ACHShould use a separate winter and summer ACHManual J will let you use blower door data (good option)(g p )Manual J will let you try a prescriptive approach (worst option)pp ( p )Manual J will let you enter your own educated input (best option)educated input (best option)

Total Cooling Load: Sensible d Land Latent

Sensible cooling load. That part of the cooling load that involves lowering the dry bulb g ytemperature.Latent cooling load. That part of the cooling load the involvesthe cooling load the involves removing water vapor from the air (dehumidification).In most of the West almost allIn most of the West, almost all the cooling load is sensible.

Psychrometric Definitions

Wet Bulb Temperature

The wet bulb temperature istemperature is measured with a wetted thermometerwetted thermometer in rapidly moving air

Infiltration Loads 0.35 ACH vs. 1 ACH

Boise=.35

Corpus Christi

=.35

Boise ACH

=1

Corpus Christi ACH=1

BoiseDiffer-

ence

CorpusChristi

Difference

Latent Load 0 4,315 0 12,329 0 8,014

Sensible Load 2 110 2 375 6 029 6 773 3 919 4 398Load 2,110 2,375 6,029 6,773 3,919 4,398

Total Load 2,110 6,690 6,029 19,102 3,919 12,412

Manual S: Cooling

Equipment Tables: What they tell you for a given set of conditions--g e se o co d o s

Total Capacity BTUHSensible Capacity BTUHp yLatent Capacity BTUH

Manual SEquipment Tables--What you need to know--

Outside dry bulbEntering (return) wet bulbEntering dry bulb CFM of fan (at real operating pressures)

Remember!

The capacity of the air conditioner is not the same as the load calculated by Manual JYou must match the load of theYou must match the load of the house at design conditions to the capacity of the AC unit at design p y gconditions

AC Capacity Rating Table

Manual J and Manual SManual 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 reall orks Don’t add o r o nThe process really works. Don’t add your own “bump”.

L Ai Fl P TLow Air Flow Per Ton

Without the correct airflow, a 13 SEER 3 t i diti i htSEER 3 ton air conditioner might be an 8 SEER 2 ton Air conditionerconditioner.Studies repeat show that 60% to 85% of all AC systems have less85% of all AC systems have less than adequate airflow

Low Air Flow = Decrease in Capacity

Percent of Ideal Air

Percent Deviation from Ideal Reduction of

CFM/TONIdeal Air

Flowfrom Ideal Air Flow AC Capacity

Reduction of Capacity

400 100% 100% 48,000 0

350 88% 11% 44,640 -3,360

300 77% 22% 43,200 -4,800

250 66% 33% 41,760 -6,240

Off the chart 55% 44% 38,400 -9,600

Low Air Flow = Decrease in Efficiency

AC Efficiency vs Air FlowAC Efficiency vs. Air Flow

1.10

Full

0.80

0.90

1.00

paci

tyR

atin

g at

Fl

ow

0.60

0.70

0.80

Cap

Frac

tion

of

Air

0.50-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0

Deviation From Full Air Flow

(F

Impact of Installation Factors on

141414R

FA]

14

pCentral A/C

11

12

13

12

13

SEER

FA]

and12

13

14

R [S

EE

12

13

14

EER

FA]

9

10

11

9

10

11

SEER

[S and10

11

ed S

EER

10

11

12

SEER

[SE

7

8

T i l I ll i7

8

9

Adj

uste

d

7

8

9

Adj

uste

7

8

9

djus

ted

S

5

6

10 11 12 13 14

Typical Installation

5

6

7

Fiel

d A

Typical Installation

5

6

7

Fiel

d A

Typical Installation

5

6

7

Fiel

d A

d

Typical Installation10 11 12 13 14

Rated SEER10 11 12 13 14Rated SEER

10 11 12 13 14Rated SEER

510 11 12 13 14

Rated SEER Courtesy of Advanced Energy

M C f L Ai flMany Causes of Low Airflow

Courtesy of Advanced Energy

Courtesy of Advanced Energy

Courtesy of Advanced Energy

Courtesy ofCourtesy of Advanced Energy

Courtesy of Advanced Energy

Courtesy of Advanced Energy

Th Ki k d H S dThe Kinked Hose Syndrome

Why do we hang ducts in attics?Why do we hang ducts in attics?

Si i D W kSizing Duct Work

Sizing duct workBigger means l t i tiless restriction, more airflowToo big toToo big to individual rooms means not enough “mixingenough mixing power”

What Creates Resistance?Friction of air moving through ducts

The faster the air is moving (velocity), the greater the frictionDevices (ACCA’s words for objects placed in the air stream) including:

Evaporator coilsFiltersRegisters and grillesg g

External Static Pressure

5

.55 .55

.5

Typical Fan Curve

ESP CFM

.3 900

.4 850

.5 800

.7 675

Undersized ReturnsSystem

should operateoperate quietly(Fast air =(Fast air =

noise)

Sizing ReturnsA l l i tA 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.

NFA300 sq. in. / 144 sq. in. = 2.08 sq. ft.Just enough for a two ton system.

R t t b oversizedReturns can not be oversized.

Quick Rules for Duct SizingFor every 1,000 Btus of furnace input there should be 2 sq. inches of duct on both the

t d th l idreturn and the supply side

Example:60,000 Btu input furnace would need 120 sq.

inches of return and supply

Quick Rules for Gas Furnaces QWith 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 ( , ) qand supply duct

The Rules Applied

Return and Return Grille Sizing

AC SIZE CFMMinimum

Size Square Minimum SquareGrille Mini-

mum Rough Sq

in Tons Sheet Metal Inches Flex Duct Inches Size (NFA) Inches NFA

1.5 638 13 133 14 154 216 288

2 850 15 177 16 201 288 384

2 5 1 063 17 227 18 254 360 4802.5 1,063 17 227 18 254 360 480

3 1,275 17 227 18 254 432 576

3.5 1,488 18 254 20 314 504 672

4 1,700 19 283 22 380 576 768

4.5 1,913 20 314 23 415 648 8645 2 125 21 346 24 452 720 9605 2,125 21 346 24 452 720 960

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

ECMs to the Rescue?CFM VS Static Pressure

1800

2000

1000

1200

1400

1600(C

FM)

PSC

400

600

800

1000

Airf

low

(

ECM

0

200

0 0.2 0.4 0.6 0.8 1 1.2

Static Pressure (IW)( )

ECMs are not magicWatts VS Static Pressure

800

900

500

600

700tt

s PSC

200

300

400Wa ECM

0

100

0 0.2 0.4 0.6 0.8 1 1.2

Static Pressure

Why Duct Sealing is Important

Inside Vs

Heating EfficienciesHomes with Furnaceand All Ducts Exterior Inside Vs

OutsideGreater effect on

ffi i th

Base Sample System Efficiency1 62.52 66.03 72.74 56.75 71.9

efficiency than 10 to 13 SEER or 80 to 90%

5 96 73.57 70.98 64.69 88.8

10 74.8

AFUEHomes with Furnaceand All Ducts Interior

11 99.012 96.7

Ducts on the Inside

Getting ducts on the inside of the conditioned space is best--conditioned space is best

But if you can’t:Seal them air tightSeal them air tightMaximize the R-valueKeep them as short as possible

Ducts on the InsideDucts on the Inside

Inside ducts don’t always look like this but the effect is the same. Duct losses are regained by the houseare regained by the house.

Ducts on the inside

Ducts Outside the House are Energy gyWasters

Attics and ventilated crawlventilated 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.

F K t Ti ht D tFour Keys to Tighter Ducts

Plug don’t Paint--Mastic should be about the thickness of a nickel to seal properlyPre-mastic as many parts as y ppossibleUse parts that don’t leak (when p (possible)Test!Test!

Mastic Used, But Still a Leak

D cts M st Be Permanentl TightDucts Must Be Permanently Tight

This Means:Tape can cover poor p pworkmanship, mastic can’tSealed with MasticTape is neither a fastener nor a permanent sealant.

Pay attention to goresy g

The Duct Leakage Test

Testing is an integral partintegral part of installing tight ductstight ducts

Heat Pump Control Requirements p q(auxiliary heat)

Install outdoor thermostat orthermostat or equivalent control and set at 35°F

Note this means using a balance point of 30º F or lower is30º F or lower is critical

Advanced Heat Pump Controls…

R t Ai R t E ?Return Air or Return Error?

Impact upon infiltration of closing interior doors with unit running

0.94

1.15

1

1.2

ur

0 16

0.42

0.62

0.4

0.6

0.8

1

Cha

nges

/ho

0.16

0

0.2Air

C

Doors open Doors closed Two doorsclosed

Four doorsclosed

All doors closedFAN ONON

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

Creating Return Paths for Balanced Flow andCreating Return Paths for Balanced Flow and Pressure

Sizing transfer grilles and ducts

75 sq in Rough opening between the.75 sq. in. Rough opening between the room and the main body of the house for every cfm delivered to the roomevery cfm delivered to the roomDesign the duct at .03 WC, with a velocity

f 350 t 400 FPMof 350 to 400 FPM

ACH: Forced air interactionsACH: Forced air interactions

Leaky ducts are a major driver of infiltrationHomes with single zone returns have significantly larger ACHs when the g y gdoors are closedLeaky ducts and closed doors are real ylosers

F Fl M t i ith Fl Pl tFan Flow Measurement is with Flow Plate

Recommended CFM/Ton is 400 to 450/ton

C R f i ChCorrect Refrigerant Charge

Sub-cooling: The removal of sensible heat from a liquid after the refrigerant h h d i t li id Thi t khas changed into liquid. 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.

Performance testing of heat pumps and AC units

Refrigeration units must have their charge checked bycharge checked by using superheat or sub cool measurements.

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

Courtesy of Ibacosy

Performance of Various Supply pp yRegisters

Courtesy of IbacosCourtesy of Ibacos

Air mixing in a zoneP i i i dPrimary air induces or set in motion the air surrounding itgSecondary air is 10 to 20 times the volume of the primary airof the primary airHence 80 cfm of primary air sets 800 to p y1600 cfm of secondary air into motionmotion

Register Throw

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

Register SpreadSpread refers to how wide the jet of primary becomesbecomesSpread decreases as throw increasesthrow increases

Courtesy of Ibacosy

High efficiency gas fireplaces and g y g pstoves

No ducts!Zone ControlRadiant Heat sourcePlus convective heat sourceheat sourceAFUE of 80%

Ductless Mini Split Heat PumpMost of the ???? does not move air, they move refrigerantmove refrigerant

Ductless Heat PumpsNo ducts!Zone ControlInverter technology allows heat pump to maintain capacity down to 0° Fp yMoves refrigerant, not airOne outdoor unit can serve multipleOne outdoor unit can serve multiple indoor units

This is a supply outlet

Can you find the heat pump?

Engineered Size Vs Installed SizeEngineered Size Vs. Installed Size

Installed Vs actual tonnage TEST!!

The Disappearing TonCooling Capacity loss in BTUs in Boise Idaho with two ton 10SEER unit All refrigerant based Cooling Capacity loss in BTUs in Boise Idaho with two ton 10SEER unit

Cooling load of house 16,900

Difference

gheating and cooling systems must be tested to assure capacity andDifference

Full capacity 19,600 2,70012% low flow 0.05 18620 1,72020% undercharged 0.25 13965 -2,93530% d L 0 3 977 7 12

capacity and efficiency. Without testing, a four ton might be a two ton.

30% duct Loss 0.3 9775.5 -7,125

Added load from duct induced infiltration3100 10,225

g

The Comfort RecipeThe Comfort Recipe

E i t i i (th b b b ti )Equipment sizing (the baby bear every time)Duct sizing (delivering the right amount of air to each room)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 jobMaking sure the insulation company did their jobMixing the air within the conditioned zone