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 Big List of DBS Rewards Points – How Much Are DBS Points Worth? (June 2021)

I chose my credit card for the miles.

(Note: this post is not sponsored, chill please!)

DBS Bank Cards - Credit Cards, Debit Cards and More! | DBS Singapore
Photo Credits: DBS

Naturally, I never bothered to check how many points I have.

Have you?

How much are these worth anyway?

Just like Grab, DBS has a huge list of rewards which make it hard for me to say what the best bang for my buck is. Check out this old interface!

oldsku

What I want to know is the highest dollars I can redeem per point.

Or, the lowest number of points needed to redeem $1.

Let’s get to it!

Naturally, the best points/dollar were from the exclusives category – naturally DBS would incentivise you to purchase one of their cards!

These aside, I’m glad to say that the KrisFlyer Miles were one of the better items at 53 points to redeem a dollar! Justifies the whole card.

Also kudos to these three sites I used as a reference to evaluate the Qantas, Krisflyer and Asia Miles.

On average, the it takes 60 points to redeem a dollar. This means each DBS point is worth about 1.6 cents.

Which means my 25891 points are worth $431.52.

I guess it’s time to use em!

I hope you found this helpful. Let me know in the comments if you want to see more posts like this.

Cheers.

The Big List of GrabPoints 2 – How Much Are Grab Rewards Worth? (Updated June 2021)

Got too many Grabrewards points?

Aiyo.

If you’ve been buying grabdeliveries during the COVID-19 Heightened Alert, or work somewhere really far from home, it might be worth checking the rewards in your Grab account!

It’s a real pain to decide what to use them on, though. Way too many options to scroll through on a phone.

I don’t want to view them on a small rectange!

Like any Singaporean, I’m looking for the best bang for my buck.

And like any engineer, I made a big excel sheet for it.

But of course.

The list is huge! Some interesting facts:

  • The largest categories were Shopping (63 items), Food & Beverage (31 items) and Services (21 items).
  • The average points/$ was 355.6 points per $. In other words, every 10,000 points would be worth about $28.
  • The most worthwhile item (ignoring lucky draws and free lounge passes) were the 70% off Spa Rael reward for 5000 points.

Check out the tables below for the top 5 Rewards for each category. I sorted them by Points per SGD – the fewer points/SGD needed, the more value you can squeeze out of your Grabrewards points!

Kudos to this post from milelion! I used his 1.8c/mile to evaluate the KrisFlyer miles.

I hope you found this helpful.

You can download the sheet here!

Cheers.

How to See the Future: All about Asset classes and the economic cycle!

Where do you park your money? Do you shift your investments during booms, recessions and slowdowns?

If you just own cash (and your CPF), that’s alright. Savings accounts may grow slowly, but they’re one of the safest investments to keep your earnings safe from market fluctuations.

However, inflation risks the erosion of your savings over time, if it grows faster than the interest rate of your bank account.

Whether you only keep savings or already deep-dive into risky stonks, you’re already making a decision about the best place to park your money!

But did you choose the best parking lot?

These parking spaces for your money are known as Asset Classes, and there are about 7 of them:

  • Cash (Savings accounts, hard cash)
  • Stocks / Equities / Shares (Includes ETFs and Index funds)
  • Commodities (Gold, Crude oil, Wheat, Live Cattle)
  • Real Estate (REITs, property, dat HDB)
  • Fixed Income (Bonds, Fixed Deposits, CPF)
  • Cryptocurrencies (Not a stock hor! Crypto is poorly correlated to other asset classes, and given the diverse sub-categories within crypto, I think it’s fair to give them a class of their own.)
  • Investing in yourself (kidding) (not really) (do it)

People shift their dough between asset classes all the time.

In economic recessions, safe slowmoving assets like cash and fixed deposits make more sense. In optimistic booms, you would wish that your money was in stonky stocks for higher growth.

Recognising where we are in the economic cycle can help you predict the future.

wooOOoOoo

Put less magically, you’ll be able to recognise the best times to shift your money from one family of assets to another.

Like a farmer waiting for ripe spring soils before planting, it helps to know the seasons!

The economic cycle has four stages: Expansion, Slowdown, Recession, Recovery.

Many things affect this cycle! Consumer optimism, changing interest rates and government policies influence how much money people are willing to fling out there, and how much they want to keep in their pockets.

Here is how most investors rotate assets in each part of the cycle:

Recovery -> Expansion

Right after a recession, optimism starts to rise and interest rates are decreasing. people are willing to borrow and invest. Industries like tourism, retail, automobiles and technology start to accumulate demand. ETFs are a very popular way to take advantage of the higher return rate of equities while spreading your risk exposure in these high times. When it becomes clear that governments will raise their interest rates, this is the best time to sell bonds and increase exposure to inflation-sensitive commodities and real estate.

Expansion -> Slowdown

While business continues to do well, fears of a pending crash and all-time-high interest rates (aka governments trying to encourage less spending and inflation) often result in a sector rotation within stocks to safer, blue-chip dividend growth stocks (think Pepsico, 3M, P&G). As the expansion slows, it’s a good time to collect your earnings from past optimism and growth by selling higher-risk stocks, equities and shares at their all-time-highs and accumulating cash and fixed deposits before the next recession.

It’s hard to predict when the economy is in a slowdown or still in expansion. In times of doubt and uncertainty, Gold is a popular hedge which may still be volatile but never go to zero.

Slowdown -> Recession

If you’ve allocated your assets well, this is you in a recession!

Source: KC Green

When the market crashes, business optimism takes a hit and investment sell-offs trigger massive drops across the economy.

Schoolkids remain blur, generally insulated, and quite happy.

In a recession, pretty much all asset classes decline. Whatever the cause, crashes are often sudden! Here, the art of moneyparking becomes more about losing less than seeking growth. Once it’s clear that an economy is in decline, goverments reduce interest rates to ease the drop, making bonds and fixed assets more attractive investments to buy.

Recession -> Recovery

At the very bottom of the recession, it is a great time to buy resilient stocks which you think will last through the recession and return again (just like SG Airlines in the heart of COVID last year…) As the mothers say, “This one is by the government … won’t fail.”

Well, your mileage may vary. Source: Google

This is the part of the market where you “Be fearful when others are greedy. Be greedy when others are fearful.” (quote by Britney Spears)

Sentiment around the very bottom of a recession is awful – people are pessimistic, companies are doing very badly, and it can often slip one’s mind to tackle the market with an aggressive, optimistic portfolio. But that is the best time. Stocks perform best over the long term, and depending on your risk tolerance and needs, having some cash around to invest more during recessions can help you emerge with a better outcome.

Using the Economic Cycle for decisions

Knowing how money flows cyclically can help you in other choices too!

For example, if you were deciding whether to buy or rent a home, and wanted to know if real estate would be a better investment than having spare cash for stocks from renting your house, you might want to look at how the real estate market has historically reacted around big crunches like COVID!

savills singapore - EDGEPROP SINGAPORE

In fact if you took the remaining, er, $2000-3000 of cash you had and grew it at a faster rate than the property market, you might end up with more value than if you bought a property!

With new eyes, you see your cash and property as two different types of investments, subject to the economic cycle in different ways.

I hope this helps you see the variety of assets out there, and how they respond to the market!

There is much more to uncover, like the different types of crypto, how to tell which part of the cycle we’re in, and more! For another time 🙂

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

Happy planning, 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.

The Ultimate Singapore Kopi O Kosong Peng Comparison Table

I dislike bubble tea.

Haters gonna hate.

Coffee tho. I’m a coffee guy. There’s something about the taste of black kopi (o kosong peng) that gets diluted with milk n sugar. That strong, bitter taste is rocket fuel to start the day.

Rocket Fuel

In my last post, I showed you how saving $3.60 on coffee could save you $10,000 at 35. The list of coffee prices was rough, so I thought I would get more specific and list all the prices of Singapore’s popular coffee spots.

I make these things to budget my life better. I hope you find em useful too.

Let’s start with cold coffee!

Note: Coffee bean only has one cold brew size, compared to Starbucks’ three.

ALSO, you can see that the maximum savings you can get is $5.50 a day on cold, black (heartless) coffee. According to my calculator (you can download it here), that’d save me $15,467 at 35.

$15,467 saved!

I thought it would also be interesting to list the prices for hot black coffee, which would eventually show us the price of ice after a quick subtraction.

The most you could save here is a comparable $5.3. Of course, a kopi o kosong is not the same as a Large from Coffee Bean. You might have to drink a little less coffee a day to make those savings. Ask yourself how much caffeine you really need.

Thought it would help to compile em all in a big graph too:

An awesome graph of coffee prices in Singapore.
Boomz.

Aaaand ice price!

Interesting to see the increase in markup on ice for smaller vendors. That extra 20c-$1.30 would amount to an extra $562 – $3,656 at 35.

I hope you found these tables and charts useful. I’ll be adding more coffee prices here as I see them, and the next topic will be on something close to heart – cookies.

<3

If you want updates for new posts, you can subscribe here:

Cheers!

The Lifetime Savings Calculator: Which kopi will save you $10,000 at 35?

I love iced black coffee! (sans the sugar.)

Living a short walk from the local shopping mall and hawker centre, my mornings could involve a kopi o kosong peng or an iced americano. Sometimes I grind & press coffee beans at home, so… aiyoh, daily trilemma. But alas, variety is the spice of life.

Being a me, I had to list the options.

  • Kopi O Kosong Peng: $1.40
  • Kopi O Kosong Peng (Marked up): $3.00
  • Iced Americano: $5.00
  • Cold Brew: $5.80
  • Homemade: $2.00

Note on the Homemade: This will depend on your beans; I use 35g of beans a cup, so a 250g bag at $14 = seven cups at $1.96 each.

Look at the difference between an americano ($5) and kopi o kosong peng – you could be saving $3.60 a day!

What would this mean in a year? Or 5 years?

The answer is complicated – interest rates, inflation and options to invest need consideration.

Luckily for you,

Excel kung fu strong.

So before we get into the sheet [free download at the end of this post] let me unpack these basics:

Interest Rates

For money saved in the bank, interest rates determine how much your saved money grows over time, or the amount that banks pay you to keep your money in their account. They would then use your money to lend borrowers and charge them that interest.

Moneysmart’s already compiled a nice, updated list of Singapore interest rates to refer to, but for the sake of this post I’ll assume a value of 1%. This means my saved money today would grow by 1% per annum over the years.

Inflation Rates

Eroder of savings. Eater of worlds. Inflation is probably the number 1 reason to invest your money, and also why my iced kopi costs $1.40 instead of $0.90 like it used to back in school.

Inflation is the rate of increase of prices of stuff (goods and services la) over time. Inflation has many causes – higher costs of stuff-production, higher wages of stuff-makers (shame on your payraise), higher demand for stuff (e.g. when people in developing citiers can afford higher standards of living) and government policies are the usual suspects.

What’s Singapore’s inflation rate? Most sources use the Consumer Price Index (CPI), which tracks the change in price of commonly purchased goods and services, including housing and transportation.

For this post, however, I’ll be using the MAS Core Inflation, which excludes fluctuations in housing and transport. More info here!

Source: mti.gov.sg

To be a little conservative, let’s go with a fixed inflation rate of 2% per annum.

Investment

A popular topic – this could bloat up a post real quick. However, it’ll be good to illustrate just what can happen without investment, so I’m going to assume an investment growth rate of 0%. Keke.

Here we go.

Savings between Iced Americano ($5.00) to Kopi O Kosong peng ($1.40) = $3.60

Saving $3.60 a day means $1,310 a year! That may not look like much, and indeed $1,310 saved in the bank (earning interest) will only have the spending power of $1,221 in 7 years.

Summing up the accumulated years of savings, 7 years of disciplined cheap coffee drinking would result in an extra $10,124 in my bank account.

If I invested those savings, say, in CPF top-ups with a guaranteed rate of 4%…

$1,310 saved this year would no longer be worth less next year, but more. Specifically, the growth percentage would look like this:

Growth of Savings = Interest Rate – Inflation + Investment Growth

= 1% – 2% + 4%

= 2%

Measly. But much better than the -1% you would be “earning” if you let your money lose to inflation in the bank.

I hope you enjoyed this breakdown of savings – let me know if there’s any

-Improvements I can make

-Clear explanations you’d like for certain pointers

-Other stuff you think I missed out

I’d love to hear them! You can post in the comments if you like.

Download of the sheet used above:

Have fun!

P.S. If you want updates on these posts, let me know by subscribing below. Cheersies.