On the back of an envelope

For some reason my mother was always concerned whether I drank enough, and of course by the time I was studying chemistry I was pretty certain I did, and that I probably could do with less.😁🍺 Water from metabolizing food My mother wasn't talking about beer of course, and while I was writing about saving tap water the other day, I was wondering how much of our recommend daily intake of water comes from eating rather than drinking. Because when we metabolize ("burn") our food, the reaction with oxygen not only produces carbon dioxide (\(CO_2\)), but also water (\(H_2O\)) in a roughly equal amount. Part of that water leaves our body as water vapour when we breath out, the rest follows the same path as the water we drink, i.e. we pee it out our lose it in the form of sweat. Calculations So how much water does an average person produce in a day when eating the recommended amount of food? The recommended daily intake of energy varies with age, weight, sex and perhaps...

Everybody  always tells us that saving rainwater is a good thing, and I guess it is from an environmental point of view. After all, producing good, clean and safe drinking water takes a lot of effort [Dutch] whereas rainwater is free. Also rainwater might actually be better for your plants too, if you live in an area with 'hard' water, and saving rainwater instead of draining it directly to the sewer system diminishes the load on the sewer treatment plants as well. So it makes sense to install a rainwater butt, a.k.a. a rain catcher or cistern, but what amount of rainwater can we expect to collect and what would be a sensible amount to store? After all, these containers cost money too. In this article we will collect some climate data, estimate some values on evaporation and combine these values with parameters like the volume of the rain container and the area of the roof we collect rain from, to simulate thousands of possible summers to see how much tap water we can save. ...

We live in a old converted farmhouse and as you can imagine for a building from the late 19th century, insulation was more or less non-existent. So ever when we moved in it has been and ongoing effort to insulate the building step by step. I started with the roof because with heat rising that should be the most effective first part you could tackle but a couple of years ago I decided to take on the wall between the residential area and the old stable. These sections together form a single building (we live in what in Dutch is called a 'langgevelboerderij', a long-façade farmhouse), but the stables are not heated at all, so the wall between the residential part and the stable is basically a large outside wall. Its surface area is about 25% of all outer walls of the residential area and it is for the most part a single stone brick wall. Now everybody (article in Dutch) always tells us that insulation is always a good investment, and with rising prices of energy that seems a n...

I have a confession to make: I am curious, but I am also a bit lazy, so the other day I wanted to know how many trucks per hour were driving along the highway near where I live. I could walk there of course, but that is quite a walk, but since I use that same highway when I drive to work, I was wondering if I could count those trucks while driving my car and still get the result I am looking for. If you were standing still near the road, it would be easy: just count every truck as it passes for five minutes, multiply by twelve, and voilá, you get the number of trucks per hour. But what if you were driving in the opposite direction at the same speed as the trucks? In Europe trucks have mandatory speed limiters restricting them to eighty kilometers per hour, so naturally they all drive at this maximum speed if they can. If you drive in the opposite direction at the same speed you would count double the number of trucks, because in the time it takes for a truck to travel any...

I am not a big drinker but I do like a good beer or whisky once in a while, so when I was considering a diet, I was a bit relieved that both my doctor and my dietitian did not try to ban alcohol all together. Even though a healthy diet ideally doesn't contain alcohol at all, one or two consumptions over the weekend is considered ok. However, recommendations are generally stated in 'units', roughly equivalent to a small glass of wine or a glass of beer. Now I don´t drink wine, but I do like both beer and whisky, so one of my friends suggested that a diet might benefit from staying with just beer, as 'hard liquor', or 'spirits', contains a lot more alcohol. Does this advice make sense? It may sound like it does, but let's look at a small list of alcoholic beverages, both beers [see note 1] and hard liquor. Brand Type ABV % Heineken Pilsener lager 5.0% Lagunitas IPA IPA 6.2% Chouffe blond 8.0% Rochefort 8 dubbel 9.2% Westm...

We’ve all been there: standing in the kitchen, smelling that heavenly aroma of a fresh loaf, and wondering—is this actually saving me money, or am I just paying for a very delicious hobby? I decided to do a quick "back of the envelope" calculation to see if my bread machine is a financial hero or just a countertop ornament. The Baseline: The Supermarket Loaf Let’s look at a budget supermarket staple: a nice, full-size Waldkorn (whole grain) loaf . Weight: 800g (approx. 500g of "solid matter", see notes at end). Price: €2.49 The Home-Baked Contender In my bread machine, I make a slightly smaller loaf (375g of dry ingredients) using organic ingredients from a local mill. Here is how the grocery list breaks down (buying in 5kg quantities, prices rounded up to nearest cent): 175g Waldkorn Mix: €1.12 200g Regular Flour: €0.32 7g Yeast: €0.10 Ingredient Subtotal: €1.54 The "Honesty" Tax: Power & Equipment To be fair, we have to account...

Hi, the idea of this blog is to verify day to day assumptions with simple back of an envelope calculations. Those assumptions could be anything from "I save a lot of money collecting rainwater in a butt", to "Isolating the outside wall of my kitchen reduces my gas bill". We might also tackle some not-so-straight-forward questions like "How to count vehicles per hour passing a point" based on counting vehicles coming towards you while driving a car. So yeah, it could go anywhere really 😀 Any calculations will be presented in a manner that is easy to understand, and I will link to sources so you can check my calculations. Be aware that I am based in the Netherlands so when I talk about prices they may be completely different for you (and will be in Euros)! So don't assume that any conclusion I might draw from my back of the envelope calculations equally apply to you. Verify, and draw your own conclusions is probably the best bit of advice I can give. An...