Question of the Day - 02 November 2023

This question and answer stimulated our curiosity and research moxie, but definitely challenged our deciphering of large-scale commercial-plumbing systems. So if any engineers out there can clarify or enhance this answer, please feel free to do so.

Hotels use a central boiler system to heat the water for the whole facility.

It used to be that the water was distributed directly from the boilers to the guest rooms and other areas of the property, kitchens and laundries in particular. The largest hotels had eight or even 10 boilers, which can be as big as a tractor-trailer. 

In the old days, that was a "hope-for-the-best" system that was perpetually in danger of running out of hot water at peak-demand times. We experienced it many times in our peregrinations; we're sure you did too.

Nowadays, the newer technology includes heat exchangers, pressure- and temperature-regulated variable-speed pumps, dedicated zone-and-loop systems, and risers (recirculation pipes through which the hot water continuously moves, so it never cools down), all computer-controlled, of course.  

These systems not only provide near-instant hot water and in as much quantity as necessary, but are much more energy efficient than the old boiler-to-shower process. The older boilers themselves have been replaced with newer models that use less gas, but still produce the same amount of heat.

We don't know for sure if they all have backup systems and built-in redundancies, but we wouldn't be at all surprised. After all, a 4,000-rom hotel like Excalibur needs to pump upwards of 200,000 gallons of hot water to meet demand, at least according to estimates we saw in researching this answer, to service all its guest rooms during peak demand from 6:30 to 9 a.m. for average nine-minute showers at two and a half gallons per minute.  

The "loop" returns the unused hot water back to the boilers to repeat the cycle. This is required, because not all rooms are rented every night and the water would become stagnant or even rusty after a while. The loop allows the hot water to be used on demand. Say you have a floor with 50 rooms and only one room is rented. That room, if occupied by a hot-water hog, will be permitted to use all the hot water allocated to all of that floor's rooms. Meanwhile, the loop keeps replenishing the allocation. The return lines send the piped water through the big loop back to the boilers; otherwise it would get cold sitting in the lines of a big empty hotel.

There are no doubt other features of these massive plumbing systems, but we hope this explains it well enough.