How Much Air Conditioning Do You Actually Need? The Ultimate Guide to Aircon BTUs and Heat Gain in Your Home

HDB Floormaps and their heat loads

Your body is a furnace right now.

who’s a lil lightbulb

In this moment, 30 trillion of your cells are metabolising, transforming nutrients into energy. This happens even when you sleep, and keeps us alive.

As your cells metabolise, they release heat!

more activity + bigger body = more metabolism = more heat

Fun Biology Fact But a Bit Too Much Information

This heat is an inevitable byproduct of the chemical breakdown of ATP (Adenosine Triphosphate), a compound that is your body’s ‘currency of energy’. It’s needed to drive your muscle contractions, move your cells, circulate blood and even get your nerve impulses going!

In the world of aircon, one of the popular ways to measure this heat is with the BTU, The British Thermal Unit.

yum, energy

An indoor aircon unit with 18000 BTU capacity is able to remove 18000 BTU of heat (and humidity).

How much heat needs removing from your home?

Let’s start with the internal heat sources. These typically mean energy-consuming things, like appliances, lights and people.

1: Identify the heat sources inside your home

The first major heat source in your home is you!

That’s right – when you sleep, your body emanates about 18 satays of heat energy!

And as you read this, little oranges of heat are radiating from your body. (The healthy choice)

This heat leaves your body by convection and conduction from your skin to the air, which is only possible when the air is colder than your skin. This is usually the case!

Here’s a screenshot of my skin temperature ranging between 33.4 and 33.8°C , taken with this sensor I have!

My core temp at the time was 38, which was more than my battery level!

During a heat wave when the surrounding air is hotter than your skin, the body actually gains heat from conduction and convection – here it can only cool itself down by the evaporation of sweat. Because humidity limits this evaporation, heat loss becomes super difficult! This is why hot, humid climates (like Singapore) are considered much less comfortable than hot climates which are dry. (Like UAE, or certain parts of Australia!)

Other than humans, electrical and cooking equipment are a source of heat gain too. Studies from ASHRAE have been done to determine the recommended heat gain for a variety of these!

The list is long.

But it’s much simpler to assume that 100% of your appliances eventually convert electricity into heat gain.

Fun Facts about Entropy – Why All Your Electricity Becomes Heat

You might think that the light energy, the sound, and the processing power that appliances produce refutes this assumption. But light bounces around your walls until its radiation is absorbed by all surfaces in a room (some escapes out the window). Sound reverberates through the air and surfaces of your house, agitating the molecules which exert friction on each other as heat! In computers, the computation performed in CPUs are simply resistance to the circuit. They perform no energy storage and do no work – simply producing heat as electricity cascades through the billions of transistors to perform instructions.

For the laptop I’m typing this post on, that means 65W!

That means my laptop is emanating about 221.8 BTU/hour, or two plain pratas of heat during the day. Yum.

What about your entire home?

Looking at EMA’s stats on Average Monthly Household Electricity Consumption, the overall average Singapore home consumes about 470kWh of electricity a month!

That comes down to a heat generation about 470000 ÷ 30 ÷ 24 = 652.7 Watts.

Which is 2227 BTU/hour!

Plan ahead!

Because the average kWh consumption of 470kWh is quite high for smaller flats, I stratified the data like this!

Almost there!

Equally important are the sources of heat outside your walls.

2: Identify the heat sources outside your home

Even a closed, empty home heats up! Before cooling you and your family, heat enters from the hot, humid outdoor air and solar radiation outside your walls.

This happens even if you had no windows!

The amount of heat is proportional to your flat’s outer surface area, which will increase depending on your floor area:

This heat travels by conduction through your window glass and the solid concrete of your walls – when one side has a higher temperature, heat will inevitably transfer to the other side!

This heat (Q) is proportional to the wall material, the surface area of the walls (A) , their wall thickness (L) and the temperature difference (T1-T2) between the inside and outside!

A simple way to calculate the total heat gain through your walls and windows is to use the BCA’s Residence Envelope Transmittance Value (RETV).

(Sidenote: RETVs can be reduced with better insulation and materials! This can be a point of pride for residential buildings. To be eligible for a Green Mark Platinum, you need an RETV of 20 W/sqm or lower.)

Let’s take the maximum RETV – 25 W/sqm.

This leads us to the final table of internal and external loads!

I’m assuming that the floor area of a condo is about the same as a 4-roomer, gasp! As we all know, they’re going down in size.

The story doesnt end here!

The heat your house expends today may change over time, which would be wise to consider.

3. Changes over Time

Consider the changes to the number (and size) of people in your home over time.

If you want to minimize the number of times you upgrade/change air conditioning units, it’s a good idea to size for the future. Most air conditioning units last 15-20 years!

Within this time horizon, how will the loads in your house change? Should you size for the largest heat load in the next 20 years? Or the load your aircon serves 80-90% of the time? It might be tempting to just buy the biggest air conditioner you can, but over-sizing your unit can be tremendously wasteful depending on the part-load efficiency.

We’ll cover that… next semester!

I hope this post helped you understand what BTUs are and how the inside and outside of your house matters when you are looking for the right size of air conditioning!

Cheers.

The Heart of Air-Con: The Artist’s Guide to Water-cooled Chiller Plants in Singapore

For the engineers and techs in the energy & sustainability sector, I am here for you.

This is your bread and butter!

And I hope to draw it for you with uncommon beauty.

What is a Chiller Plant?

So.. air conditioning takes up about 50% of energy consumption in our commercial buildings.

The cold is costly!

The energy which powers Air Conditioning simply moves machines that throw human heat outside of a building.

Liddat

This sounds simple, but actually involves a long chain of machines, passing the heat to each other.

Woah.

This magical process works mainly because of one principle:

Hot things transfer heat to cold things.

In a building, this happens a few times:

  1. Your muscles and organs (37°C) heat your skin (36°C) in your body.
  2. Your skin (36°C) heats the supply air (18°C) from your air-conditioning, making return air (28°C).
  3. The return air (28°C) heats a chilled water supply (7°C) in the aircon unit to a chilled water return (12°C) .
  4. The chilled water (12°C) heats a very cold refrigerant (5°C) in the chiller’s evaporator, to 6°C.
  5. The refrigerant is compressed (6°C -> 50°C) into a high pressure vapor in the chiller’s compressor.
  6. The hot refrigerant (50°C) heats condenser water (30°C) in the chiller’s condenser to 35°C.
  7. The condenser water (35°C) heats the ambient air (29°C) in the cooling tower…
  8. … which is where all our heat goes! The ambient. The sky. The outside.

Is this bad for the environment?

Technically, without air conditioning, we would walk around heating the air anyway.

What these machines do is essentially increasing the gradient between hot and cold.

That’s no problem, right?

The thing is, not all machines are efficient – they produce their own heat while working.

Due to inefficiency!

And the energy they consume from power plants.. requires more heat to generate too! Ideally, 100% of the electricity we supply to machines is converted into the useful work we use the machines for. However, some of this heat is inevitably converted to heat and sound produced by friction between mechanical parts and electrical resistance.

The more machinery we run to operate an air-conditioning system, the more heat is generated in the world. Sounds kinda funny, but we don’t really feel the effects of this when we’re chilling indoors!

On to the machines themselves!

1. The Air Cycle (Air Handling Units)

  • Humans do stuff. Their muscles and organs get warm, and this heat is transferred to their skin, which is transferred to the air around their skin.
  • This hot membrane of air transfers heat all over the air! Hotter air particles have more kinetic energy, and jiggle faster than their cold neighbouring particles. These hotter particles rise above their inactive neighbours who remain relatively still (AKA Meritocracy). At the ceiling of a room, a fan sucks in these hotties, blowing them past a very cold chilled water coil inside an Air Handling Unit (AHU). This coil’s water is at about 7°C. That’s cold!
  • The hot jiggly particles collide against this coil, losing their jiggliness to the coil surface. The cold water inside the coil takes gets heated from 7°C to 12°C. Meanwhile, the air is cooled from ~28°C to about 18°C. The resulting average room temperature is somewhere around 24°C, which is the temperature your thermostat tries to maintain.
  • The cycle repeats. Cold air hits human, human heats air, hot air heats water, hot air becomes cold. Ugga bugga.

2. The Water Loop

  • Chilled water just took some heat, and needs to drop it quickly. It flows through the Chilled Water Return pipes to the chiller plant, where it will be cooled back to 7°C again, by the chiller.
  • Chillers have a simple function – Make chilled water cold again.
  • They do this by passing the 12°C water through super-cold refrigerant fluid, which is about 5°C in the evaporator.
  • After the 12°C water transfers its heat to the refrigerant, it leaves the chiller at 7°C, on its merry way back to the AHUs.

3. The Refrigerant Loop

  • Air passed heat to water. Water passed heat to refrigerant. Refrigerants are fluids with ideal properties for containing and releasing energy rapidly, but I’ll be skipping those details for now (low boiling temperature! Rapid phase-change material!),but in summary is a fluid that can be very cold at room temperature. This enables it to be the ‘colder thing’ which the already-very-cold 12°C water can give its heat to.
  • Once the refrigerant takes this heat, it is compressed into a hot, high-pressure vapor, which enables it to now be the ‘hot thing’ to transfer heat to another water loop, the condensor water loop.

The whole operation of a chiller looks like this:

Which I hope makes sense of this!

4. The Condenser Water Loop – Throwing it all out

  • In the chiller’s condenser, hot refrigerant now passes its heat to water (Yes, a separate circuit). This water goes to a cooling tower, those huge grilled-boxes you see on top of many buildings in Singapore.
cooling tower vs. chiller – cooling towers on roof
Source: waterchillers.com
  • Cooling towers do exactly what you do to cool soup – blow air over it. The hot water is trickled down the serrated walls of metal, and air is sucked through these walls by a huge fan in the centre of the box’s ceiling.
  • The water that collects at the bottom is at about outdoor temperature, where it is pumped back to the chiller to be heated again.
  • This stage is called Heat Rejection, the final stage of any air conditioning cycle. It is where the heat of hundreds of warm humans is amalgamated and tossed back out into the air, where it is more easily forgotten.

Is this all necessary?

We’ve all suffered the heat here – air-con definitely makes it feel better. While I don’t have air-conditioning at home, I seem to survive quite well with fans. Even a cool breeze outdoors on a sunny day makes me feel comfortable enough to forget the humidity.

I’m not so sure what the best way is – what do you think?

Is it too much for some comfort?

How Much Floor Area Do You Need?

HDB Floorplans

We all face Choice Overload. In Singapore, house options have thousands of sizes and styles and prices – which one do you choose?

On top of the ~80,000 houses available, 1600+ renovators are available. There are hundreds of millions of possibilities.

How to decide sial.

I find it helpful to list your minimum requirements. Specifically, the things you need a house for.

If I lived alone, my house would be for:

  • Reading/Drawing/Tablework
  • Exercise
  • Cooking/Baking
  • Sleeping

For this bare-bones existence, I’d need a…

  • Desk+Chair
  • Empty space
  • Oven
  • Fridge
  • Bed
  • Wardrobe
  • Washroom

And that would look like:

I added a window. I need.

This box is about 12 square meters, or 130 square feet.

So now that I know I need 12sqm, browsing property sites is a little less scary. Looking at typical HDB sizes, even the humblest of flats is enough:

  • 1 Room / Studio: 36 sqm / 388sqft
  • 2 Room HDB: 45sqm / 484sqft
  • 3 Room HDB: 65sqm / 700sqft
  • 4 Room HDB: 95sqm / 1023sqft
  • 5 Room HDB: 115sqm / 1238sqft

What about couples? The budget life is hardly glamorous, but nonetheless the mental exercise of defining your minimum requirements (perhaps with a woke spouse) makes navigating the ocean of buy/rent options a little easier.

Budgetbox v2 is about 16 square meters, or 177 square feet. Amazingly, a 1-room HDB is still larger.

Knowing the minimum size for a liveable room gives us mental building blocks to imagine greater needs – how much space do you need if you wanted:

  • A child’s bedroom? (e.g. 16sqm + 12sqm = 24sqm) (< 1room HDB)
  • A livingroom? (e.g. 16sqm + 8sqm = 24sqm) (< 1room HDB)
  • Housing 3 children? (e.g. 16sqm + 12sqm + 12sqm + 12sqm = 52sqm) ( 2-3 room HDB)
  • etc.

Adding the building blocks is a simple guideline. However, with multiple people, amenities like kitchens, desks and washrooms can be shared for further economy.

You can add literal blocks to get a picture of the minimum floor space needed:

Nice big livingroom.
Kids room < Couples’ room size, of course.
These lucky kids get a room each.

Your mileage may vary – you might need a balcony, or decide you don’t need a big livingroom, or want some separate dining areas etc as a minimum. Nonetheless, here’s a summary of the experiments above for reference:

I personally would like some spoils in the house like a balcony, a garden, a rooftop view etc. But if I can’t find these spoils, at least I know what my minimum requirements are, and whether they’re met. I hope this experiment brings some comfort to your decisions too.

I’d love to hear your feedback! Do you think I:

  • Missed any points out?
  • Should do a clear explanation on any bits?
  • Could go deeper in certain areas?

You can let me know your feedback in the comments, I’d love to hear suggestions to make these mental tools more useful.

Happy house hunting, cheers.

The HIFAS Buy vs Rent Calculator

Buy vs Rent Calculator Panel

Figuring out loans is confusing!

I’m not a broker or in finance. Like everyone, I will be paying for a home at some point. I just want to know how much my purchase costs.

Luckily, I know excel.

There are some useful calculators online which I used as cross-references:

A key feature of this calculator is seeing how much your initial loan increases (e.g. 150% of its initial value) if you stretch it out over a longer period of time. For example, if you take a$800,000 loan at a 2% interest rate, paying it over…

  • 10 years: Total sum paid is $872,182 (110%) at $7,361 monthly
  • 20 years: Total sum paid is $956,748 (120%) at $4,047 monthly
  • 25 years: Total sum paid is $1,000,687 (130%) at $3,391 monthly
  • 30 years: Total sum paid is $1,045,684 (130%) at $2,957 monthly
  • 35 years: Total sum paid is $1,091,698 (140%) at $2,650 monthly!

See how the tradeoff works? You sacrifice liquidity every month for a lower total amount. In the long term, it may look like a good idea to pay off your loan quickly, but you really have to be able to give up that amount of monthly cash. This article covers both sides of the dilemma quite well I think!

If you’d like to play with it and add your own figures, you can download the calculator here:

Lemme know if you:

-Think I missed anything out

-Want a clear explanation of something

-Think of any improvements I can make

Would love to hear your feedback to make this a more useful calculator.

Cheers.

Buy or Rent? A Look Into The Multiple Timelines of Your Life

Imagine you died.

A timeline of years of life.
100 is #goals.

Looking back on your timeline, how many houses did you live in?

Most of us think of:

A timeline of houses lived within one life.
Just three homes!

If you live outside of Singapore, where houses are cheaper, maybe more of a:

I base these on countries like Canada or the States, where housing is a little cheaper than Singapore. Certainly helps to widen the variety of options in one lifespan.

For the lucky bunch of us who need less variety and pretty much know what they want, the options are simpler:

#buyitforlife

In these fantasies, the first house you buy is the last house you buy.

gasp

Assuming you can confidently live by yourself/yourselves, you know what house you (and your spouse) want to live in, age in, kidz in, retire in and expire in.

If you can’t afford a loan yet, rentals might be a waste of the savings+investments you’re building to afford buying this One Home.

So in conclusion…

If you crave less variety and have researched enough to have high certainty in the house you want, save up to buy.

Of course, if you have the luxury of being in a multi-generational flat, and are comfortable living with parents, you may not have to worry about buying at all. This might seem outlandish if you subscribe to the idea of independent living, but 3Gen flats are still a thing here.

I’ve met adults with children who live in the same flat as their parents, who have no intention to move out. It’s not for everyone, and it’s not for me, but I can see how 3Gen flats are a supremely convenient, secure and frugal choice.

Sound boring?

To some, staying in the same box for 10-20 years gnaws at the soul. Comfortable routines and neighbours may be valuable to some, but life can look short. The world, your oyster, is ever ripe for the picking (well, opening). (tasting?)

What tempers variety is children and affordability.

Children

Children of parents who travel a lot don’t recount a great experience (Check out this Reddit and this Quora). While moving is exciting and makes your kids super-adaptors, it’s hard to build lasting relationships with friends who you’re ripped away from after years of bonding. LDRs are hard enough.

Super Adaptor

My advice to variety seekers who also want kids is to go forth and move to a new setting/view/style, but relocate near the same schools and amenities to help your children grow some deeper social roots in a community. Most friendships take years to form, developing the ability to maintain long relationships later in life. See the Reddit and Quora links above for more perspectives about this!

For readers who don’t want kids, its a lot easier to move houses frequently, as long as it makes economic sense to you. Which brings us to…

Affordability

Looking long term and buying a dream home for your 60-year old self can be tough for your cash!

If you’re looking to buy, say, a landed property for your retirement higher than 1000sqft (approximately a 4-room HDB flat, or 27 king-sized mattresses), most of those will cost you upwards of $800,000 SGD.

Click here to see how many mattresses you can fit into other HDB-sized floorplans.

Take this scenario:

Comparison of Rent and Taking a Loan

If you took an $800,000 loan for 35 years at a fixed interest of 2.6% (rates are lower now but it’s a good average), your future selves woulda paid $1,183,692 in total – 150% more than the initial loan amount. Renting 5 increasingly expensive different places over the same 35 years could save you $108,492.

$100,000+ That might look measly in a conversation about real estate prices, but if you put that sum to investments you could be saving much more than you think!

So buy or rent?

My personal opinion is that if you haven’t tried living in your own place yet, the experience is absolutely worth it (The woke salaryman covered this pretty well). If you are just trying things out first, go for a rental and go low until you learn what you really want. Renting provides the flexibility of GTFO-ing when you’ve had enough of one place.

The kueh lapis strategy. Try a lot, learn, then decide.

Otherwise, jumping into a multi-year commitment to pay a monthly mortgage can be stressful if you:

  • Are unsure of what house you want for the next 30 years
  • Don’t have career stability (mortgage payments are harder to get out of than rents)
  • Don’t have enough savings to bolster 6-12 months of expenses on a rainy day!

However, once you’ve figured out what you want, and can afford a loan to get it, and have enough savings to buffer a year of low/no revenue, I think that buying is a legit option.

I approach the Buy vs Rent question like a buffet.

A Buffet.
A Buffet.

At a buffet, I’m faced with 20 options at the table.

In plate 1, I sample a small part of each food on the menu.

Some food sucks. I take note and avoid it in plate 2.

Some food is not bad. I will add it to plate 2 just to double-check if I love it or not.

Some food is MUST HAVE. Smoked salmon. Eclairs. The good stuff. These go in plate 1, 2, 3, 4 and probably be part of my last bite.

By plate 3 or 4, I already have my faves down, and don’t bother with the weak options which were in plate 1. For the notbads, I’ve decided whether or not they should be dontneeds or musthaves. Applying this to housing choices, it’s like knowing what your core wants are over time, and what things are just fluff. (Do you really need that lawn?)

Before I pick a home I gotta payfor+stayin for 30 years, I sample the whole menu to figure out what I like and don’t like, lowering the risk that my eventual choice is one I grow tired of after 15 years.

I can’t speak for what the 70-year old me might want, as tastes change, but I intend to make his decisions easier by properly planning how I spend my money today.

I hope this post helps you in your own path. Let me know if there’s..

-Anything I missed out

-Any clear explanations you like

-Anything I coulda covered better

I’d love to hear your feedback! You can post in the comments to let me know. Cheers.

Choosing Your House by Floor Area – What does a Sqft and a Sqm Look like?

I’m the typical 20+ year old nearing my thirties – checking out housing options in Singapore, itching to move out of home. Inspired by talks with peers and this post from The Woke Salaryman, it’s now a habit to check out Propertyguru, 99.co and SRX from time to time get a sense of the real estate here.

Photos give me a clear picture of what living in the place will be like.

Price tells me how much I’d be sacrificing monthly on a mortgage or rent.

Floor Area … doesn’t ring any intuitive bells. I can’t ‘feel’ what a 45sqm studio or a 700sqft HDB flat looks like.

So I thought it would be helpful to feed my intuition by starting with relatable lego blocks, then scaling them up to fit some common floorplans in Singapore. Hopefully this helps you too!

The Basics

A Square Meter (sqm) is a unit of area (Length x Width) defined as the area of a 1m x 1m square.

In imperial units, the same square would be 10.76sqft.

1m = 3.28ft

1sqm = 1m x 1m = 3.28ft x 3.28ft = 10.76sqft

Intuitive lego block 1: mattresses!

Queen size is veh lucky.

In a nutshell,

  • Super Single beds ≈ 2sqm
  • Queens ≈ 3sqm
  • Kings ≈ 3.5sqm

On to the houses!

Singapore’s housing sizes change over time, so I used the amazing Teoalida’s research to narrow down a rough floor area size for 5 types of flat:

  • 1 Room / Studio: 36 sqm / 388sqft
  • 2 Room HDB: 45sqm / 484sqft
  • 3 Room HDB: 65sqm / 700sqft
  • 4 Room HDB: 95sqm / 1023sqft
  • 5 Room HDB: 115sqm / 1238sqft

Immediately, before going into pictures, we can divide these by mattresses to get a rough sense of their size:

  • 1 Room / Studios: ~10 Kings + 1 Super Single (36.6sqm/394sqft)
  • 2 Room HDB: ~13 Kings (44.95sqm/483.9sqft)
  • 3 Room HDB: ~18 Kings + 1 Queen (65.13sqm/701.1sqft)
  • 4 Room HDB: ~27 Kings + 1 Super Single (93.95sqm/1011.3sqft)
  • 5 Room HDB: ~33 Kings + 2 Super Singles (115.29sqm/1240.9sqft)

And now, some graphics.

For this one, I think it helps to simply think of 35 sqm as 10 king sized beds.

Roughly 3 more kingbeds equate to 9 more sqm!

Things start to get huge for the 3-rooms, the main difference being the twinning of the bathrooms and the bedrooms. Here, its easiest to think of it as 65sqm ≃ 700sqft ≃ 18 King beds.

With an additional bedroom and extension of the livingroom space, the 4-roomer is about 1000sqft, which is roughly 27 king-sized beds.

For the luxurious 5-room flat, the living room gets an extra space in this project, which is roughly 115sqm, about 33 King beds plus 2 Super Singles.

Hope the pictures above and the lists help you visualise floor areas for your own home searching! if you have suggestions or comments to make this more helpful, type them to me in the comments or contact page. Cheers!