Sizing an AC why we use Manual J , writesoft or simmilar

Summary

This script discusses the complexities of air conditioning unit sizing, emphasizing the importance of heat load calculations over the outdated method of square footage per ton. It highlights how modern construction variations, such as different window types, wall materials, and insulation, necessitate precise calculations for efficient and cost-effective cooling. The speaker warns against the common mistake of over-sizing AC units, which can lead to premature compressor failure and poor dehumidification, advocating for a heat load calculation to ensure optimal performance and energy savings.

Takeaways

• 🏠 Sizing an AC unit is crucial for ensuring the correct rate of heat removal from a house.
• 📊 Traditionally, a 'heat load calculation' was used to size AC units, which involved considering various factors like wall types, windows, doors, and insulation.
• 🔍 Modern methods for sizing AC units include using computer programs like 'Manual J' and 'Write Soft', which simplify the calculation process.
• 🏡 The variety of building materials and designs today, such as different types of windows, walls, and doors, makes the heat load calculation more complex but also more precise.
• 🌡️ Over-sizing an AC unit can lead to poor performance, reduced dehumidification, and increased wear and tear on the system.
• ⏱️ An oversized AC unit may not run long enough to allow for proper oil return and refrigerant cycling, which can damage the compressor.
• 💡 Under-sizing an AC unit can actually be beneficial as it runs longer, dehumidifies better, and can lead to more energy-efficient operation.
• 🌡️ It's important to size an AC unit not for the hottest day of the year but for the typical conditions to ensure comfort and efficiency.
• 💼 The speaker emphasizes the importance of a professional heat load calculation over the outdated 'square footage per ton' method.
• 💡 A real-life example is provided where a homeowner experienced improved comfort, reduced energy bills, and a longer-lasting AC system after correctly sizing the unit based on a heat load calculation.

Q & A

Why is it important to correctly size an AC unit for a house?

Correctly sizing an AC unit is crucial to ensure it effectively removes heat from the house at the right rate, providing comfort and energy efficiency.

What factors contribute to the complexity of modern AC unit sizing compared to the past?

Modern AC unit sizing is more complex due to a variety of factors including different types of windows, wall materials, ceiling heights, door types, insulation, and various other construction elements that affect heat load.

What is a heat load calculation and why is it important in AC unit sizing?

A heat load calculation is a detailed assessment of the heat generated within a building and the amount of cooling required to maintain comfort. It's important for accurately sizing an AC unit to ensure it can handle the cooling demand of the space.

What are some of the old methods mentioned for sizing an AC unit, and why are they considered outdated?

Old methods included using a simple square footage to tonnage ratio, which is outdated because it doesn't account for the numerous variables in modern construction that affect heat load.

Why is it not advisable to size an AC unit based solely on the hottest day of the year?

Sizing an AC unit only for the hottest day of the year can lead to inefficiency and higher energy costs, as the unit may be oversized for the majority of the time and not run optimally.

What are the consequences of installing an oversized AC unit in a home?

An oversized AC unit can lead to poor dehumidification, increased wear and tear due to frequent cycling, higher electricity consumption, and reduced comfort levels in the home.

How can modern tools and software, like Manual J, assist in the process of heat load calculation for AC unit sizing?

Modern tools and software streamline the heat load calculation process by guiding users through a series of questions and automatically calculating the necessary AC size based on the inputted data.

What is the significance of considering the direction of windows (north, south, east, west) in heat load calculations?

The direction of windows affects how sunlight enters the house and thus influences the heat load. Windows on the east and west sides can cause more heat gain due to morning and evening sun, respectively.

Why is it incorrect to size an AC unit based on the number of 'thumbs' that can cover the house from a distance?

Sizing an AC unit by the number of 'thumbs' covering the house is a humorously inaccurate method because it does not take into account the many variables that affect heat load and cooling requirements.

What is the impact of an undersized AC unit compared to an oversized one?

An undersized AC unit may not be able to cool the house effectively, but it is generally better than an oversized unit, which can lead to more significant issues like poor dehumidification, increased energy consumption, and premature equipment failure.

Outlines

00:00

🏠 The Complexity of AC Sizing

The paragraph discusses the intricacies involved in correctly sizing an air conditioning (AC) unit for a home. It highlights how the process has evolved from simpler times with fewer construction options to the present, where a multitude of factors such as window types, wall materials, ceiling heights, door types, and insulation levels must be considered. The speaker emphasizes the importance of a heat load calculation over the outdated and oversimplified method of sizing AC units based on square footage alone. The paragraph also touches on the advancements in technology that have made the calculation process more efficient, such as computer programs and laser measurement tools.

05:00

📊 Evolution of Heat Load Calculations

This paragraph delves into the historical context of AC unit sizing, contrasting the old methods with modern approaches. It points out that in the past, when homes were more uniform, a simple rule of thumb based on square footage was sufficient. However, with the advent of more diverse construction materials and designs, this method became outdated. The speaker advocates for the use of computer programs like Manual J and WriteSoft, which facilitate accurate heat load calculations by asking detailed questions and considering various factors about a home's construction and usage. The paragraph also humorously critiques the outdated practice of sizing AC units based on square footage, suggesting it's as reliable as guessing the size with one's thumb.

10:04

❄️ The Impact of Oversized AC Units

The speaker in this paragraph explains the negative consequences of using oversized AC units. They describe how an oversized unit can lead to rapid cooling but fails to dehumidify effectively, resulting in higher energy consumption and reduced comfort. The paragraph also discusses the technical aspects of how an AC unit operates, emphasizing the importance of allowing sufficient runtime for the refrigeration cycle and oil return to the compressor. The speaker uses the analogy of a car engine to illustrate the inefficiency and potential damage caused by an oversized AC unit, which cycles on and off too frequently without reaching optimal operating conditions.

15:04

🌡️ Correct Sizing for Efficiency and Comfort

In the final paragraph, the speaker reinforces the message that AC units should be correctly sized through heat load calculations to ensure energy efficiency and comfort. They share a personal anecdote about a friend whose AC compressor failed due to an oversized unit, which led to insufficient oil return and premature compressor death. After downsizing to the correctly calculated size, the friend experienced improved cooling, reduced energy bills, and a more comfortable home environment. The speaker concludes by advising against the old square footage method and encourages the use of modern calculation tools for accurate AC sizing.

Keywords

💡Heat Load Calculation

Heat load calculation is a process used to determine the appropriate size of an air conditioning (AC) unit for a specific space. It takes into account various factors such as the size of the space, insulation, window types, and local climate to calculate the amount of heat that needs to be removed to maintain a comfortable temperature. In the video, the speaker emphasizes the importance of heat load calculations over the outdated method of sizing AC units based on square footage alone, illustrating how modern homes with diverse construction materials and designs require a more precise approach.

💡Insulation

Insulation refers to materials used to reduce the flow of heat in or out of a building. It plays a crucial role in the energy efficiency of a home and affects how an AC unit should be sized. The script mentions that insulation can vary in thickness and type, impacting the heat load calculation. For instance, a house with poor insulation would require a larger AC unit to compensate for the heat that penetrates through the walls.

💡Windows

Windows are a significant factor in heat load calculations due to their impact on a home's energy efficiency. The video discusses how different types of windows, such as double pane, triple pane, or those with low-E glass, can affect the amount of heat that enters a home. The orientation of windows (north, south, east, or west) also matters because it influences how much sunlight and heat they receive at different times of the day.

💡Ceiling Height

Ceiling height is an important consideration in heat load calculations because it affects the volume of air that needs to be cooled in a room. The script mentions various ceiling heights, from standard to vaulted or loft ceilings, each of which would require a different amount of cooling capacity. A room with a higher ceiling would need a larger AC unit to effectively cool the space.

💡Doors

Doors, like windows, can influence the heat load of a home. The script discusses different types of doors, such as solid wood, metal, or insulated doors, and how they can impact the efficiency of an AC unit. For example, a poorly insulated door can allow more heat to enter a home, necessitating a larger AC unit to maintain a comfortable temperature.

💡Orientation

Orientation in the context of the video refers to the direction a building or its components (like windows) face. It's important for heat load calculations because it determines the amount of sunlight and heat a home receives. The video explains how east- or west-facing windows might receive more direct sunlight and thus contribute more to the heat load than those on the north or south sides.

💡Oversizing AC Units

Oversizing an AC unit is a common mistake mentioned in the video. It occurs when an AC unit is too large for the space it's cooling. This can lead to inefficiency, as the unit cools the space too quickly and then cycles off before the refrigerant and oil can circulate properly. The video warns against this practice, explaining that it can lead to higher energy costs, reduced comfort, and a shorter lifespan for the AC unit.

💡Dehumidification

Dehumidification is the process of removing excess moisture from the air, which is an important function of an AC unit. The video explains that an oversized AC unit may not run long enough to effectively dehumidify a space, leading to discomfort and potential health issues due to high indoor humidity. Properly sized AC units can maintain both temperature and humidity at comfortable levels.

💡Energy Efficiency

Energy efficiency is a measure of how well a system uses energy to perform a task, such as cooling a home. The video emphasizes the importance of energy efficiency in AC units, particularly in the context of heat load calculations. A properly sized AC unit will be more energy efficient, saving on electricity costs and reducing the environmental impact of cooling a home.

💡Climate

Climate refers to the average weather conditions of a region over a long period. In the context of the video, climate is a critical factor in heat load calculations because it influences the amount of heat an AC unit must remove to maintain a comfortable indoor temperature. The video suggests that homes in hotter climates may require different AC sizing considerations than those in cooler climates.

💡Square Footage Per Ton

Square footage per ton is an outdated method of sizing AC units based on the assumption that a certain number of square feet requires one ton of cooling capacity. The video argues against this method, stating that it's too simplistic and doesn't account for the many variables that affect a home's heat load. Instead, the speaker advocates for heat load calculations that consider factors like insulation, window types, and local climate.

Highlights

Sizing an AC unit is crucial for ensuring the correct rate of heat removal from a house.

In the 50s and 60s, houses had limited variations in construction materials, simplifying the AC sizing process.

Heat load calculation was a method used to size AC units in the past, taking into account various factors of a house's construction.

Modern houses have a wide variety of construction materials, such as different types of windows, walls, and doors, complicating AC sizing.

Windows now come in various types, including double, triple, or quadruple pane, with different gases and coatings, affecting heat transfer.

Wall coverings, ceiling heights, and door types have diversified, impacting the heat load on a house.

The number of people, kitchens, and bathrooms in a house, as well as their sizes, affect the heat load and AC sizing.

Computer programs and tools like Manual J and Write Soft have simplified the heat load calculation process.

Laser distance measures and computer programs can now perform a heat load calculation in minutes, compared to hours in the past.

The old rule of 'square footage per ton' is outdated and can lead to incorrect AC sizing.

Oversizing an AC unit can lead to poor performance, lack of dehumidification, and increased wear on the system.

An oversized AC unit may cool the air quickly but fails to dehumidify and maintain comfort at high outdoor temperatures.

Underestimating the size of an AC unit can be better as it runs longer, dehumidifies more effectively, and is more energy-efficient.

AC units should be sized to handle the hottest days of the year, not just occasional peak temperatures.

A heat load calculation is essential for proper AC sizing and can lead to significant energy savings and improved comfort.

A personal account of a homeowner who experienced压缩机 failure due to an oversized AC unit, and the benefits of downsizing to the correct size.

Emphasizing the importance of not relying on outdated methods like 'square footage per ton' for AC sizing.

Transcripts

all right sizing an AC unit sizing a

student is it's really tricky because we

want to make sure we're taking the heat

out of the house with the correct rate

so we want to size an AC for the house

right so back in the like back in the

50s and actually so much more more like

the 60s when you buy houses then you

pretty much will had one option of walls

it pretty much one option to wall types

had pretty much one option for windows

you want windows we're not he had pretty

much one option for doors you'll want a

door or not you pretty much had one

ceiling height when the ceiling was

height he had one option for

installation do you want insulation or

not and it was it was pretty simple

there was a lot of choices was there but

even back then it that we call a heat

load calculation have some plans that my

grandfather had from when he was

building houses and they did what you

call a heat load calculation we sized AC

units for a heat load calculation

nowadays how do different types of

windows can you buy if you're gonna

build a house a lot like a new ones all

the time you have difference between how

many panes of glass there are you have

differences between what kind of gas

they put between the panes double pane

triple pane quadruple pane how well the

gas is sealed is the art on gas or co2

gas or whatever the kind of gas and then

you have the type of metal they use the

steel the glass and then they have the

type of coating to put in the outside

what kind of rate radiant heat that

they're blocking on that you have on top

of that low E glass it's could you put a

little that radiant heat out and then

you have the ones that automatically tip

now you can press the button and it

tense it to keep the all of these

different types of glass how many

different types of walls do you have now

on wall coverings in the outside you can

have insulated siding you could have

regular siding you have reflective

siding silver siding brick siding wood

siding fake log cabin siding you can

have 2 by 4 walls 2 by 6 wolves to buy

10 wolves the insulation in the wall is

have are six or eight are 12 you

can have the foamed walls that seal

everything

ceiling heights

how many different types of ceiling

heights we have now oh man you got six

foot you got seven foot eight foot nine

foot 10 foot you got the ones that are

the the vaulted ceilings now they got

the rounded Half Dome ceilings you got

loft ceilings you get all different

sizes of ceiling heights what different

types of doors do we have now

gosh doors ellonija you want a solid

wood door what a partial wood door what

a fix wood door yo a wood door doors and

glass little metal doors metal insulated

doors what kind of door frame you have

the walls inside of the walls inside

insulated not insulated the roof there's

gonna be a metal roof that reflects Heat

a white roof a black roof of black

shingle roof that absorbs a massive

amount of heat which is crazily popular

here that which should never be here

what kind of floor D have is a concrete

floors and insulated concrete floors

that appear in beam floors that appear

in beam insulated floor is it stilts

what kind of flooring is that we have

Plus how many people's of it in house

you know some houses they only got a few

people living there some houses have

extended families living in there's lots

of people lots of body heat how many

kitchens are there in the house how many

bathrooms are there in the house of

those bathrooms what kind of what's the

size of those bathrooms and what's the

size are they full bathrooms partial

bathrooms what kind of showers they have

what kind of ventilation set up in that

bathroom computers how many computers

are there going to be in that house

because computers put up a tremendous

amount of heat plus trees what kind of

trees on the outside is there overhang

where is this house located is it going

to be located in a cooler climate warmer

climate dry climate humid climate what

kind of ground covering integers is

there outside is there rocks is gonna

reflect heat into the side is going to

be grass out there that absorbs

something heat energy there's a lot that

goes into size again it oh and going

back to the windows real quick are the

windows on the north south east or west

side of the house or maybe they're north

east or north west or any combination

because if the sun is shining through

these windows in the morning as this

room going to be the same temperatures

the room on the other side or the other

ones and then an evening when the sun's

going down and it's shining through a

different set of windows is that going

to play a part in the heat load

calculation absolutely so a lot of

information goes into sizing at units so

when it comes to sizing unit you do what

you call a heat load calculation and my

day way what we call the short sheet and

it was a page an entire page of

calculations we had to measure the walls

facing each direction how much Wolf's

face was there what kind of

installations in the walls of those

walls how much that spaces windows how

many peoples in the house all this stuff

is called a short sheet it was an entire

page long and it was the shortcut

version it took a little bit of time to

do a heat load calculation now you got

it simpler now you got computer programs

you have what we call manual you get

write soft it's manual J there's a book

called manual J which all of its sides

done but there's a book called write

soft and it's a computer program bring

your laptop in and you go through and

you size everything up you put all the

numbers in and ask you questions and it

builds you a blueprint and then it tells

you the size of it and now you get the

laser things

laser distance but deep but you can get

the hole size of this room like that and

you just put those numbers in you can do

a Hilo calculation like 30 minutes now

or before it took us a few hours to

really get a good heat load calculation

and it's going to size what size the air

conditioner is on top that it sizes how

much CF film you need in each room so

they have the proper air flow free room

it's a heat loop calculation it's

beautiful it's awesome it's great it's

simple but back in the 60s and 50s when

they would do these old-fashioned

calculations you had everything was the

same all the walls are the same the

windows everything was the same so one

guy figured out you know it really works

out to square footage because everything

was the same when he did it everything

was the same so he said there was so

many square foot per ton and it it

really it worked all through the 60s 50s

70s even the 80s has started to get a

little rough but it worked so well

because in the 80s you started having

more options and then 90s that was gone

I think of it in 90's we think with you

guys y'all you probably think Oh a 90s

house is old

that's a new house right and then you

have then the house built in 2000 how

many options were there in types of

doors windows and walls in a house in

2000 you think it goes the same as that

was back in the 60s no even in the six

of the heat load calculations so what

you have is people that heard this old

rule from long time ago my old rule from

a long time ago and it's simple and we

love simple and so what they started

doing was saying oh so many square foot

per ton that's what's that's what house

that's what size you need so we have a

saying nowadays to help the sticks of

people remember it square foot per ton

proves you're done

square foot per ton proves you're dumb

you should never size a house off square

footage if you want the size went off of

square footage is it easier way what you

do is you go ten paces from the house

which is usually right about the curb

and you count how many thumbs cover the

house and each thumb was a ton of

cooling works just as well in that

ridiculous

it wouldn't be ridiculous the size the

house with your thumbs oh cemani my

thumbs cover the house yep well it took

four thumbs that's a 4 ton unit Oh your

house when it took 2 thumbs if I have

this face in the other direction Oh nope

only two thumbs I'm on the curb

two thumbs you're good you're good to go

it's insane right absolutely insane

people are sizing units off of square

footage still today still today turtle

oh yeah sweet a square foot yeah you're

you're good now it may give you an idea

of if you're in a ballpark or not but

it's it will not give you any way

possible the size of the unit for that

house though worst thing you can do is

oversized that a/c never over sized an

a/c in America wants think bigger matter

yeah right so the problem that oversized

a/c

is everything about how the a/c works it

takes about 15 minutes those

refrigeration cycle to get up and

running when this refrigeration cycles

up and running I have to bring in low

pressure

or pump out high-pressure vapor get this

pressure built up get that pressure drop

get the airflow moving get everything

balanced out I need oil returned and the

oil flows with the refrigerant to get

back to my compressor right it takes a

bit of time if I if I let it run for

less time and the unit shuts off that

oil may start building up in the

evaporator or building up over here in

this other line and the oil doesn't make

its way back to the compressor and then

the compressor starts up without oil so

you want that compressor to have a

certain amount of run time to D humidify

the air I need the move air across this

evaporator at a certain rate if I move

the air across this vibrator for a

certain amount of time and a certain

rate

I can D humidify it but if I only pull

it across for a little bit and shut it

off I don't get to pull that moisture

out Plus that of a critical it stays

moist and a lot of that air is

evaporating right back into that

moisture is evaporating right back into

the air so when we have a unit that's

oversize what it does is it comes on and

it cools the air very fast air is light

by the way if you guys knew that so it's

way easier to cool air than it is to

cool water because air changes

temperature very very quickly and very

easily so as I move the air through this

evaporator coil I can go boom quickly

take the heat out of that air and I'm

blowing that cool air into the room and

when I drop the temperature of that room

very very quickly I drop the temperature

that room quickly the air is the other

thing that's really changing but what

else is in this room tables moisture

tables people walls floors everything so

the air very quickly heats back up and

the unit comes back on and very quickly

cools it back off and then it heats up

very quickly and it's on off on off on

off on off on off before we get the

refrigerant cycling through before I get

the oil return and this unit wears out

plus the amount of electricity it takes

to start this compressor is significant

and it wears the unit out and uses way

more electricity and it's fun is

comfortable and also it doesn't

dehumidified now that's not a problem

here with the humidification but in any

other

place you go you don't dehumidifies it's

a big issue you can have the humidity

inside the house way higher than the

humidity outside just because you don't

dehumidified so by running that system

oversized it wears it out faster it also

ends up making it uncomfortable and if

you live anywhere else it's a causes the

minification problems so if you have a

unit that's under sized and it'll

actually be better because it'll run

longer and not and it'll dehumidifier so

the other thing is you don't sigh as a

unit for the hottest day of the year

you don't Assizes it for that one time

you might need it when I go and buy a

car I don't buy a car rated for the

engine for that one time that I need to

pass somebody in a two-lane road I want

to get a crowd get around them as

quickly as possible I don't buy my

engine like that I don't buy a NASCAR

engine for that one time I may need to

pass somebody or that those very few

times a year I need to pass somebody to

get around right yes I saw your book

your okay so you want to make sure that

the system size properly the AC units is

occasionally going to need to run when

it's 115 degrees they eat when it's 115

degrees it's only there for an hour or

two a few times a year really and truly

we think 115 well it stays over a

hundred significantly for sick of a

significant amount of time here but you

can't get the whole entire year and how

many times it's actually at 115 how many

hours it is it's very seldom at 115 and

when the temperature outside is 115 the

air conditioner shouldn't be able or it

should be running past its maximum it

should be staying on constantly when

it's 115 degrees outside your air

conditioner should run non-stop to

maintain temperature non-stop which is

running as its most efficient by the way

should run non-stop continuously 115

degrees outside is in your air

conditioner cycle off

oversized oversized when it's 115

degrees outside

that unit should be maxed out it should

be on its own it's its whole way when

you're passing somebody on a two-lane

road you want to get around them you

have it floored right to get around them

it's like saying oh you know what I'm

gonna really need a really goose it to

get around this car I'm gonna give it

3/4 throttle here right that is an

oversized AC for sure so we want to make

sure we size it correctly for the house

maintain temperature humidity it's

called a heat load calculation a friend

of mine he had his AC and his compressor

went out really nice high-dollar trained

unit really nice unit and he comes to me

and he was talking about the compressor

and says man the compressor dies so we

got to find out why it died and he went

through everything and said man II

couldn't find anything about why it died

he was getting quotes for it and said

well it's sighs your house so he did a

heat load calculation and the unit was

one entire ton oversized an entire ton

oversized what was happening was the

units coming on off on off on off on off

no oil return and it burned out the

compressor so I said you need to put put

the right size unit in there and you're

gonna be okay he goes man it's it's

Vegas it's hot I really don't want to

put a smaller unit in like well did you

do a heat load calculation yeah yeah had

it done put that size in but you know

what if it's what if it's too small I

said did you do a heat load calculation

yeah I did then that's the size you put

in it will be okay but I'm just afraid

it's gonna be too small I was like why

you asking me I mean at this point so he

said okay I'm gonna trust you and he put

in an entire ton smaller than he was

supposed to have that or that he

originally had and he called me back a

few weeks later and he says his tie this

thing is cool like it's never cooled

before he goes it runs longer and it's

so much more comfortable in the house he

even keeps it at a higher temperature

because it just generally feels better

in the house at a higher temperature

and it runs smooth runs quieter

everything runs better

he called me back two months later and

says taya I've got my last two electric

bills they are way less money because I

will have this new air conditioner paid

for in just the savings of my electric

bill in about two years at this rate

that's a heck of a payback in two years

I tell you so yes we do size units we do

size with the heat load calculation

square feet per ton stay away from that

now if somebody says oh square feet

don't call them dumb all right and I'm

not saying that but I'm saying in your

mind you need to be going mmm screws

your dumb a lot of people just got hung

up on you know one of two things either

the old school way of doing it not

actually what appreciate it or doing a

heat load calculation is too complicated

they they're afraid of it they don't

know how to do it nobody's ever showed

them how to do it so they don't know and

it's just easier to say Oh 35 psi in the

tire I'll just just add till you get it

like 70 psi refrigerant for our 22 be

fine I'll just make sure this was not

over like a hot day like you know 325

you should be good right soft and then

also Manuel Jay Manuel Jay

have you seen my spelling that's fair I

don't know it's Google both of them that

Angus is a double you always wanted to

change my name to WI the righ T so it

could be mr. right all right any

questions no no questions