Eli5: How does a hotel always have hot water for every occupant?
In: 1975
Giant industrial boilers that create large amounts of hot water… these are much larger than home hot water heaters and can keep a steady flow of lots of hot water available.
Multiple water heaters, tankless water heaters, and much bigger water heaters than you would expect.
Note hotels don’t *always* have hot water for every occupant. I used to occasionally travel to Toronto for business, and one of the hotels I stayed in was pretty nice, but if I wanted an early-morning shower it could take 10 minutes or longer for hot water to make it up to my floor.
Some have really larger boilers and storage tanks. Others have multiple smaller instant boilers around the building.
Essentially the system is designed to handle the load.
Residential systems are often under powered or “right sized” for the owner that installed it, but that doesn’t mean that sizing works right for everyone.
Unlike your home hot water heater, hotels have one giant hot water heater for the entire building – not just for guests, but also for the kitchens, laundry facilities etc. And when you’re talking about a boiler for a hotel, you’re talking thousands of liters and massive amounts of BTUs. No single person or use, even if they left the water on continuously would even put a dent in the supply from one of these things.
The key to having hot water in a hotel is recirculating hot water. In your house, when you turn off the tap the water stops moving, and starts to cool off. Later, to get hot water, you have to run the tap to flush out the cold water in the pipe and get to the hot water.
This is very inefficient, it wastes water and the energy that went into making it hot.
Recirculating hot water uses a small pipe to allow the water in the hot pipes ot continue moving when all the taps are off. A tiny, very energy efficient pump, slowly moves the water back to the hot water heater’s tank. That way the water in the hot pipe is always hot, and when you turn the tap the water is hot right away.
I had this feature in several houses, and it’s super convenient.
Travel to a third world country, and then revisit your use of ‘always’ and ‘every’. Sweeping generalizations are almost always incorrect.
Lots of answers here, which is great. But trunking efficiency has not been mentioned. There’s unit of measure called and erlang [https://en.wikipedia.org/wiki/Erlang_(unit)](https://en.wikipedia.org/wiki/Erlang_(unit)) that tries to encapsulate some this concept.
Works like this: Assume average human needs 50L of hot water per day, but that figure varies by +/- 10%. How many litres of hot water would you need for a 100 person population to have a less than 1% chance of running out?
About 5050L. Because all the + and – 5L of each of the 100 people actually smooths out. For each person who is having a heavy usage day, someone else was in the pool, or left early for their flight, etc.
An Erlang is the measure of trunking efficacy for long distance telephone (back when we didn’t have gobs and gobs of internet bandwidth to carry it all). You didn’t need 1 connection for every customer, and the more customers you had the fewer per-customer capacity you needed to plan for.
Same applies to internet bandwidth. Because not everyone’s usage at any give time period (second, minute, hour, day) is the same and it’ll all spread out.
Right now I’m working on a high rise with apartments and they don’t have hot water tanks, they have steam heat exchangers. Basically the water is on a circulation loop and is constantly flowing through a radiator that is meshed with another radiator filled with medium pressure steam (230°-250°)
That steam is constantly keeping the domestic hot water at an extremely high temperature (180ish°), then flows to a mixing valve to temper it with cold water down to like 100ish° depending on the person setting it. That tempered water is what goes to your shower mixing valve and you fine tune the heat some more. This is common for hospitals, dorms, hotels etc that have a steam system, my city has municipal steam provided to the larger high rises paid as a utility like gas and electric.
Other systems will have large water heaters that do something very similar but don’t need a heat exchanger. They just feed high quantities of very hot water to the mixing valve that as needed all automated with thermostats so it just kicks on whenever the water line drops below the threshold. This can be done with or without a storage tank.
It is actually much easier for a hotel than for a home. The average hot water need for a family of five is probably one shower + one sink + one appliance (dishwasher or laundry) in a 1 hr stretch. Of course, sometimes three people might be in the shower, with two sinks running, and two appliances running, all within an hour. So the hot water needs to be sized for that brief peak demand, which might be 275% of average.
In a hotel, the peak demand is much closer to the average demand. Say a hotel of 300 guests averages 25 showers per hour during morning/evening rush (say 6-10am + 4-10pm). Even if 1/3 of the hotel needs to shower after an early concert (100 ppl from 8-10pm) that’s only an extra 25 people/hour = 200% of average.
In operations theory, this is called “pooled capacity.”
Of course, the larger scale also enables more efficient hot water production and storage.
Also, the hotel isn’t always full so often runs below peak.
You don’t always have hot water at home? Even in apartment complexes? That’s certainly a very normal thing in Switzerland to just have hot water everywhere at any time.
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