Energy needed for himan survival in urban scenario

How much energy needed to survive in central European climate with very low income?

Depends on location and time of the year.

Let's assume mild winter case scenario. November to February, -0C. Area for living 50m2.

1. Keeping warm temperature inside the house at 16-17C: Compressor heat pump 5A, 220AC=1.1KW with duty cycle 50% is around 500W, or Close to 10KW per day.

2. 1-3KW for cooking, lights and washing machine. Actually for assorted needs it may vary up or down drastically. I'm taking it as an average.

For example having 3 times a day tea or coffee: about 200W already. 1 g of water by 1 degree Celcius or (1 Kelvin) equals 1 calorie. Thus 1 Liter from 20C to 100C boiling stage is 334 720 Joules (335KJ) or 93 Wh, but raising that temperature within say 3 minutes it is 1860W instant power, BUT for 3 min only. It is still the same 93W. Please note: in reality, no way to heat water with 93W source as heat will escape faster then water temperature rise to boiling temperature. Realistically with 80% efficiency it is more like 120Wh.

When we talk about some sort of action like heating water or compressor or electric motor, it is always in Watt hours this signifies for how long that action took place. Because energy used in watts has to be calculate in the account time.

I on purposely use electrical terminology Watts because in most of urban survival we going to use  electricity.

If you would try to burn wood to heat 1L of water, it will be in theory if we have around 50% efficiency as during burning lots of head goes to atmosphere and with an average dry wood. At this point we will skip the boring calculations and give you the result: around 0.1Kg or 100g.

But how often can you see people using wood to boil or cook in modern world?

Cooking 3kg or 3L pot meal will be 5 times as much as for boiling 3l water. Thus it is around 1500W of electrical power to cook an average dish for 3 people. Please do not use watt hours the same a just watts. I use it very loosely because I can keep tracking of which is which, but inexperienced reader might insanty come to erronies conclusion by using W and Wh at the same time. I keep thinking as Watts needs to be accumulative during the day and thus 10KW for heat pump + cooking 1 meal +

Also we are not taking in assumption the transportation. It is assumed the "survival" modality and human will travel by his own power.

Also we assuming food is given, which is very bad assumption. But to simplify case for calculation we need to start somewhere and move to more complex scenario. Also this is NOT post apocalyptic scenario but rather low or no income person a a family with very minimal means for their living. We will discuss other, more isolated/autonomous scenarios later but for now

Most likely 15KW per day or at most 700W per hour

2. Possible help by wood furnace. 1kg wood is about 2.6KW energy

1m2 wood is around 400kg, thus for 1 month in the -10C winter, house for a man requires: 30d x 11Kw=330Kw or 330/2.6=127kg of wood or 0.3m3.

As I was writing this, I got very doubtful. Most likely it is close to 2m3 of wood or 6m3 of branches.

This consumption has to be estimated very scrupulously because each particular usage case may vary 100 times.

For example: people always makes the same value for one light bulb on or a cup a tea boiled in an electric tea kettle. Not really...light bulb is 15W for very bright LED light and tea kettle is 700...2000 watts! Obviously left for 24hr 15W bulb will present 360 Watt and teakettle for 5 minutes with 1000 watt power is only 84W used in 5 min segment. But if it is only 2 hours of light, then it is only 30W

Another example is a small thief(or multiple thief) we always have in our houses: it is a charger for the cell phone or something left in the wall outlet constantly plugged. I may not believe, but some of them consume around 1W of energy per hour. Not much, but it is whole day and 360 days per year... thus it is 9000 watts per year! And imagine your whole house is full of those little or big things constantly left to be powered. It will add up rather quickly.

Let's assume we are very disciplined people and really really surviving.... So we only use energy to stay alive.

In this case the estimate is around 15KW per day if we don't use any extra sources of heat and around 5KW if we use wood/oil/gas heaters or some sort of extra heater to keep 17-18C

Please write your comments in the forum section. People will appreciate your real observation.

I will try to come up with simplified calculator for energy usage as we are all living in such a different circumstances and climates that my estimate can be way off chart from your case scenario.

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