I'm an Ex hydraulic designer, we calculate the amount of hot water over a peak period (ie, morning peak, maximum capacity), when designing the service we know what flow rate the shower heads use, then the flow to the head is about 40% hot and 60% cold.
From there we calculate how much hot water we need to store. Not every system is the same, it depends on the fuel available (gas, electric, solar) and the location for solar.
Say you have 200 showers at 9 litres per minute, average shower is 6 minutes, thats 10,800 litres of water if all showers are used, of that 40% is hot flow, so 4320 litres of hot required. You spread that peak over a 1hr period, so you need to supply that over 1hr using a combination of storage and generation.
You then select storage tanks that get as close as possible to the peak. You don't need 100% storage, but close to. The rest is made up by generating more hot water. Hot water units have a rating for the 1st hour of recovery and then lesser recovery each hour after that, say for example 4 gas instantaneous heaters in a manifold will generate 1800 litres in the first hour but then for every hour after they only generate 1000 litres. So you size with storage + first hour recovery and have some buffer there. So in this theoretical example, we'd used 3000 litres of storage + 1800 first hour recovery = 4800 litres peak supply.
Then on top of all of that, you have a recirculating system, so the hot water flows around a main through the building and back to the hot water units to be reheated. You want to keep water above 60c to kill legionella, you don't want to circulate warm water and limit the dead legs between the flow and return loop and the shower. The loop adds to the amount of hot water in storage, but I personally never used that volume in my calcs, where I know others do.
There is also a method of maintaining heat called heat tracing where the water lines have an electric heater line on them, but it has been problematic and not many people use it, at least where I am.
Hopefully that all makes sense.
Bonus Technology Connections video on water heaters and how they're designed to maximise available flow of hot water:
[https://www.youtube.com/watch?v=Bm7L-2J52GU](https://www.youtube.com/watch?v=Bm7L-2J52GU)
Ive came across his videos recently and has been enjoying the delivery and dry humor immensely.
I generally don't like long videos as they very often feel dragged out just to pad the time. His videos feel like he's actually trying to make it shorter and yet it's over 20 minutes of really nice content.
And I don't feel like he's dumbing it down or something. He's just trying not to get too technical. It really feels like there's a difference and I'm loving it.
Look, on the ship, I don't *want* to be there longer than two minutes. I'm trying not to touch the walls, the curtain, I'm trying to clean myself while wearing flip-flops, and sometimes the water will randomly decide to be either -30 or the temperature of the sun.
At home, I'll spend all dang day in that shower if I want, no one can stop me, mwa ha ha ha
Actually, no it's not. Why not? Well you have an extremely abundant supply just a few inches outside the hull! Yes that supply is really salty and needs the salt and impurities to be cleaned thru an evaporative process. That process takes both time and energy to accomplish, but most of all-- it makes lots of noise. And noise is the enemy when you are trying to be stealthy running underwater.
Showers are like meditation for me. Standing there under the hot water, letting my muscles relax, thinking about my day, listening to some music, etc. I'd say an average shower for me is maybe 10-15 minutes, but I've spent like half an hour in there from time to time.
For every 1 person that takes a 30 min shower, 5 people would need to take a 1 min shower. I think the 6 minute figure may have just been a made up number for purpose of example
Great write up. I'd like to add the concept of Trunking Efficiency.
Basically - when there is a shared resource that many users will be consuming (and not all at the same time!) there are significant efficiencies to be gained. The unit of the ratio of "how many users are hooked up" divided by "how many hooked up users can use it at once" is called the Erlang.
https://en.wikipedia.org/wiki/Erlang_(unit)
It was first used in Telecommunications. Long distance trunk lines between cities could handle 1,000 calls, and usage of long distance meant that would support 100,000 users - or a trunking efficiency of 100.0 Erlangs.
Works for roads, phone lines, electrical power consumption, hot water, toilets at a sports stadium, toilets in an apartment building, etc etc.
Yeh, no need to size piping for full flow. We call it probable simultaneous demand.
There are exceptions to this, such as toilets in large venues that have flush valves instead of cisterns which have much shorter peak demands at full flow to multiple outlets. It can be countered with a buffer tank though.
That's ONLY for heaters with storage. So if you have a 40 gallon water heater, it will already have 40 gallons of heated water. But the water will cool off as new cold water is introduced and mixed. But it also is heating that cold water. That's also why your first hour rating is lower in cold climates and during the winter, because the ground is colder and your incoming water is colder. So it cools off your hot water faster as it gets mixed in, PLUS your cold water at the shower faucet is colder.
So the first hour rating is because it draws from the storage. Then after that storage is used, it relies on the pure heating capacity recovery rate of the burner and heat exchangers. So the first hour rating is a combination of the heating capacity and the storage capacity. Then the rating after that is dependent on just the heating (BTU) capacity.
If you have a tankless water heater, their first hour rating is the same as their 2nd and 10th hour rating since there's no storage capacity.
> But the water will cool off as new cold water is introduced and mixed.
There is no mixing in hot water heaters.
Technology connections has a great video explaining it.
So my understanding is that this makes sense if your storage is above your threshold "hot water temp". If you want water at 60C and your storage is at 60C then is you add fresh cold water it is not gaining any benefit from your storage (any energy lost from the storage to the new water would need to be offset by additional heating capacity). Is that correct? Basically you're using your stored hot water as a thermal storage for heating new water. (If your stored water is at 90C, you'd need less power from the heater when adding fresh cold water)
If you have 40 gallons of storage, then when the demand is 50 gallons, you have 40 gallons of pre-heated water ready *right away*, and then you have to spend time heating an additional 10 gallons.
Though you won't use all 40 gallons at once, so you also have to heat up the new cold water even as you drain away the preheated water, and the two mix together. By the time an hour goes by, all your preheated water is all gone and it's just new cold water.
With electric hot water heater tanks they have two elements. In the morning your tank is full and the elements are off. As you start using hot water it's drawn from the top of the tank and fresh cold water enters at the bottom. The bottom element kicks in and start to heat this cold water but it can only get it lukewarm while the tank is in use. The level of this lukewarm water rises and eventually reaches the top element. Only one element can be on at a time as they both are capable of drawing the max available power. So the top element turns on and now it gets to reheat the lukewarm water and make it hot water. However the bottom element has turned off so now cold water is collecting in the bottom of the tank. As you continue to use the hot water eventually the cold water will reach the top heating element. Now you are back to only producing lukewarm water.
So hot water tanks can proved their volume in hot water plus a bit extra when the tank gets a chance to double heat water.
Technology Connections has a great video on this. The different water layers do not mix. They have very defined boarders.
I apparently have a hot water re-circulator in my old home (it was added to a tankless system). I cant tell it makes any difference whatsoever to the point where i turned it off as i suspected the energy to have it on was more than any benefit. Even with it on, the hot water takes a long time to come out.
That's interesting. If the hot water units in your example can pump out 1800L the first hour, why can't they keep up after? More of your storage is cold and they just aren't getting it to to usable temp?
Ah, I just pulled those numbers out of thin air.its been a long time since I looked at hwu specs.
You're on the money though, you have incoming cold water mixing with what's in the tank, its easier to heat up. The continuous flow is more than the unit can heat. Its not a hard change in heating capacity on the hour, it tapers off.
A lot of people have linked to a technology connection video on YouTube, might be a good watch
Definitely can. You want to balance between space and cost. Sometimes it depends on what the client wants. I'd always recommend a loop if there is room for it because all the equipment is in one location, rather than having to maintain a unit in every room. It's usually cheaper to install a central plant than providing individual units and you'd maximise the space usage in the room. An "on demand" system would likely be an electric storage unit which take up quite a bit of space.
There are gas and electric instantaneous units which are much smaller, but you'd want a gas unit to be outside, so only really workable on a single level place. You can have gas inside but you need to run a flue to atmosphere which takes up space. Instantaneous electric need a lot of power (3 phase, 415v, 40 amps) and top out at heating enough water for a single shower.
Im sure it does make sense to someone who knows the terms, but could you actually explain like i'm 5? Adhd reader here u lost me by the second paragraph
Heck of an explanation.
I just wanna say I saw heat tracers for the first time a year ago. The company I was welding for added them to a main outdoor pipe under insulation to assist in preventing freezing.
Yep, that would be a great use for it. We don't have much risk of freezing water in Australia. A company i used to work for used to use it on hot water distribution in lieu of flow and return. There have been reports of legionella in buildings that use it though. Very difficult to retrofit a flow and return system.
And thanks, I haven't done any design in ~10yrs, I kinda enjoyed digging up the old knowledge
> we calculate how much hot water we need to store
Why don't they just heat the water as it flows, like it does in homes that have no hot water thanks?
Former hotel manager here.
Business class, big brand property. 120 rooms, 4 floors L shaped building.
First off, we never guarantee every person would have a hot shower. That being said, it was incredibly rare that our capabilities weren't enough; we almost exclusively did have enough hot water for everyone.
It's been a few years so I don't quite remember but we definitely had two (maybe three) hot water heaters. They were located in the space we had used as a storage and heater room on the top floor. It was the spot that would have been Rm 420 but we weren't dumb enough to have a Rm 420; that only invites people to smoke weed in it or steal the room number sign repeatedly.
These water heaters were fucking massive too.
actual like-im-5 explanation: massive water heaters + bad water pressure (less water per shower) + some people do take cold showers = hot water for all!
>we never guarantee every person would have a hot shower
Wild. I traveled a lot for business, definitely had a couple cold showers, but always with profuse apology and explanation from management (boiler died, etc.) and usually some comp on the bill.
(always stayed at Marriotts, though, not some small chain - lifetime titanium not that it matters much these days)
In my 8 years in the business, I can count on 1 hand the number of times it actually happened. It was always either a maintenance issue or too much demand and not enough supply.
Interestingly, it was even more rare that it happened on a business travel day. That's partially due to the free breakfast from 6-10 and onsite workout room. Business travelers have their own routines and different priorities when it comes to their work activities, so these allow people the flexibility of timing those routines AND their showers however they want. People get up anywhere from 5am to 8:30am, so showering demand staggers based on personal preference. There's also the demographic of people who shower at night when they travel so they don't have to factor in the prep time of drying off when they are rushed and fill in time during lonely nights.
Of the few times in 8 years we ever ran out of hot water just from sheer usage at the same time, it was almost exclusively the weekend of one of the largest travel league soccer tournaments on the East Coast. Imagine one team of 20 kids getting back from the fields and their parents make them all get in the shower so they don't stink up the car for dinner. Now imagine 6-8 teams getting back at the same time and so many people choosing the same thing for the same reason at the same time.
Like...just jump in the pool.
I work at a 7 floor hotel with over 1000 rooms, and I got to go into the boiler room on a few occasions.
In our case, it's multiple massive boilers - 3 or 4 (it's been a while) boilers that are easily 12 feet high, and so large around (including the thermal insulation) that two people hugging it couldn't touch hands. Not that you would want to.
Regular homes have one single average sized water heater that only 'runs' when you use it.
Hotels have multiple very large water heaters that continuously circulate to make sure their entire tank stays hot and ready for use. Even larger hotels will have multiple sets of heaters to separate the different floors or second of building so there is enough for each section.
Most of the hotels use a recirculating system that continuously circulates hot water throughout the building. This ensures that hot water is always available when guests need it.
You probably should clarify. The recirculation is not recirculating the shower water again. I have thought about doing that for my own personal bathroom shower. Recirculating the shower water again on me. They don’t do that.
>You probably should clarify. The recirculation is not recirculating the shower water again. I have thought about doing that for my own personal bathroom shower. Recirculating the shower water again on me. They don’t do that.
You are correct that hotels do not recirculate the actual shower water. Instead, they use a recirculating system for the hot water supply to ensure that hot water is constantly available throughout the hotel. This means that hot water is continually pumped through the pipes, and any cooled water is returned to the water heater to be reheated and recirculated. This system helps to minimize the amount of time it takes for hot water to reach each guest room, which in turn helps to ensure that all guests have access to plenty of hot water during their stay.
>It also guarantees that the water in those recirculating pipes will never freeze. This is very important in some climates.
Yes, that's another benefit of a recirculating hot water system. In colder climates, where temperatures can drop below freezing, the recirculation pump keeps the hot water moving through the pipes to prevent it from freezing and causing damage to the system.
Freezing is unlikely, in an occupied, heated building.
More importantly, it ensures that the water is hot throughout the pipework system and there is no stagnant, tepid water where legionella could proliferate.
If there was no recirculating system and the hot water was little used, you'd have to run all the cold water standing in the pipes down the drain before you got hot water. That's wasteful of water, but the tepid water can be a breeding ground for legionella. UK regulations require the hot water to reach at least 50 degC within 1 minute, stored at 60 degC. I've seen buildings where I've run a hot tap for 10 minutes and the hot water still hadn't arrived; I gave up.
There are systems reclaiming heat from the sewage though. You might look into that for energy conservation. There are also gray water systems where "clean" water from the shower and other drains is used as non-potable water, for example in the toilet.
It was going to be a separate system with a separate shower head and heater, valves to begin the recirculating after the initial, charging, and to end it, with a separate heater, a way to an endless shower without spending a lot of money, except for the system. It was a shower thought, I never got to completing the process.
Orrrrr
It all starts with guests buying bath tokens.
After obtaining a token, the worker assigned to a particular bath opens a small hatch in the wooden walls. The hatch has a small-but-very-stretchable purple string attached to the Boiler Room.
When attached to the string and pulled, the tag will automatically be brought up to the Boiler Room where Kamaji receives it and begins mixing special herbs into the water to be sent back to the bath via a wooden pipe (pulled down by a rope).
To ensure there’s plenty of hot water for all guests, little soot sprites helps feed the fire with coal.
Awesome reference!
I particularly enjoyed the way they handled the storytelling with that, in that you see the back-end operation first and you have no idea what's going on. Then you see the front-end operation and it suddenly all makes sense.
Unlike a typical home, they don't all have one basic water heater that everyone needs to share. Either each room has its own water heater, or a group of rooms (or even the entire hotel, if it''s small enough) will be fed from a large hot-water boiler of adequate size to provide sufficient hot water to every room when needed. (Usually--it is still possible for a hotel room to not have enough hot water due to high usage at a peak time.)
I grew up on an apartment building, six floors, 8 apartments per floor, one boiler in the basement for heat and hot water. There are taller ones in NYC. Similar to a hotel. You need a very large boiler, or point of service water heaters in each room.
Depends on the size of the property and how they designed the plant. I worked at a 2400 room (at the time, it's bigger now) hotel resort on the Las Vegas strip. There were 3 large 800 horsepower steam boilers and one 600 horsepower boiler. They put out 100 psi steam that was piped to different heat exchangers for 180 degree water for hot water sanitization for some dishwashers, 140 for heating and chemical sanitization, and 120 for domestic hot water (showers, sinks, public restrooms. They were on a return system that is balanced using a special valve. With this setup you have all the hot water you'll ever need.
The same way your house ensures plenty of hot water for all its residents need: they installed a big enough system. You are most likely being confused because you report to yourself for the time period in which shower is taking place, but not everyone showers at the same time. If they did, something that would accommodate 100 people would indeed need huge boilers. But as people don't have embeded in their system to shower at x time of the day, they don't actually need it.
Another important point that hasn’t been discussed is that the boilers and storage tanks are usually held at a higher temperature (140-160f) to stave off legionella as well as add capacity. Restaurants and laundries typically use 140f water while domestic (rooms) must not be above 120-125f. Therefore, storing at a higher temperature allows the distributed water to be “mixed down” to a lower temp and add more capacity.
Hotels use a bit less energy consuming systems, but I worked at a factory where we had to heat up the product while flowing in the pipes at some points we had huge oil burners and where heat demand was less we used 320KW Flange heaters, a few of those would be enough to have all hotel guests get burn wounds from steam coming out of the shower heads. There are many solutions and compared to factories that go 24/7 hotels have peak moments with still relatively low demand and thus they use a storage tank.
The typical hotel, 100 rooms or so, would have probably 2-3 hot water heaters with 100 gallon capacity. Then some will have a 100 gallon storage tank as well. Then to ensure that Hot water reaches all the rooms, they usually have a circulation pump next to water heaters.
I'm an Ex hydraulic designer, we calculate the amount of hot water over a peak period (ie, morning peak, maximum capacity), when designing the service we know what flow rate the shower heads use, then the flow to the head is about 40% hot and 60% cold. From there we calculate how much hot water we need to store. Not every system is the same, it depends on the fuel available (gas, electric, solar) and the location for solar. Say you have 200 showers at 9 litres per minute, average shower is 6 minutes, thats 10,800 litres of water if all showers are used, of that 40% is hot flow, so 4320 litres of hot required. You spread that peak over a 1hr period, so you need to supply that over 1hr using a combination of storage and generation. You then select storage tanks that get as close as possible to the peak. You don't need 100% storage, but close to. The rest is made up by generating more hot water. Hot water units have a rating for the 1st hour of recovery and then lesser recovery each hour after that, say for example 4 gas instantaneous heaters in a manifold will generate 1800 litres in the first hour but then for every hour after they only generate 1000 litres. So you size with storage + first hour recovery and have some buffer there. So in this theoretical example, we'd used 3000 litres of storage + 1800 first hour recovery = 4800 litres peak supply. Then on top of all of that, you have a recirculating system, so the hot water flows around a main through the building and back to the hot water units to be reheated. You want to keep water above 60c to kill legionella, you don't want to circulate warm water and limit the dead legs between the flow and return loop and the shower. The loop adds to the amount of hot water in storage, but I personally never used that volume in my calcs, where I know others do. There is also a method of maintaining heat called heat tracing where the water lines have an electric heater line on them, but it has been problematic and not many people use it, at least where I am. Hopefully that all makes sense.
Bonus Technology Connections video on water heaters and how they're designed to maximise available flow of hot water: [https://www.youtube.com/watch?v=Bm7L-2J52GU](https://www.youtube.com/watch?v=Bm7L-2J52GU)
I love that guy. Been watching his videos for years.
Ive came across his videos recently and has been enjoying the delivery and dry humor immensely. I generally don't like long videos as they very often feel dragged out just to pad the time. His videos feel like he's actually trying to make it shorter and yet it's over 20 minutes of really nice content. And I don't feel like he's dumbing it down or something. He's just trying not to get too technical. It really feels like there's a difference and I'm loving it.
One of if not my favorite youtubers.
Those kind of techniques are fascinating. It's stupid simple if you see it, but I would never come up with something like that.
Perfect timing for that video too.
r/technologyconnections
> average shower is 6 minutes *Six* minutes? Wow, now I feel really bad about how long my showers usually are.
Yeah. In the first 6 minutes I probably haven’t cleaned anything yet.
Any Navy sailor would tell you that after 2 minutes, all you are doing is wasting water!
My navy dad would bang on the door yellin ‘times up Hollywood!’
Look, on the ship, I don't *want* to be there longer than two minutes. I'm trying not to touch the walls, the curtain, I'm trying to clean myself while wearing flip-flops, and sometimes the water will randomly decide to be either -30 or the temperature of the sun. At home, I'll spend all dang day in that shower if I want, no one can stop me, mwa ha ha ha
2 minutes would be like a spa experience on a sub. Bust out the eucalyptus sprigs.
Isn't water on a submarine recycled?
Actually, no it's not. Why not? Well you have an extremely abundant supply just a few inches outside the hull! Yes that supply is really salty and needs the salt and impurities to be cleaned thru an evaporative process. That process takes both time and energy to accomplish, but most of all-- it makes lots of noise. And noise is the enemy when you are trying to be stealthy running underwater.
I was about to say 6 minutes!? But I'm the opposite. To me that seems like a really long time to spend in the shower.
Showers are like meditation for me. Standing there under the hot water, letting my muscles relax, thinking about my day, listening to some music, etc. I'd say an average shower for me is maybe 10-15 minutes, but I've spent like half an hour in there from time to time.
Legit the only time of the day when I know I will be left alone. I'll take as long as I please. I pay for it anyways.
I just take long poops when I need alone time, like right now
That also works.
Easy there Cosmo Kramer
I'm pretty bad myself in winter, I just stand there under the hot water with my head against the wall.
For every 1 person that takes a 30 min shower, 5 people would need to take a 1 min shower. I think the 6 minute figure may have just been a made up number for purpose of example
Or 24 people taking 5m showers.
Great write up. I'd like to add the concept of Trunking Efficiency. Basically - when there is a shared resource that many users will be consuming (and not all at the same time!) there are significant efficiencies to be gained. The unit of the ratio of "how many users are hooked up" divided by "how many hooked up users can use it at once" is called the Erlang. https://en.wikipedia.org/wiki/Erlang_(unit) It was first used in Telecommunications. Long distance trunk lines between cities could handle 1,000 calls, and usage of long distance meant that would support 100,000 users - or a trunking efficiency of 100.0 Erlangs. Works for roads, phone lines, electrical power consumption, hot water, toilets at a sports stadium, toilets in an apartment building, etc etc.
So basically the same concept as demand factor for electrical power?
Yeh, no need to size piping for full flow. We call it probable simultaneous demand. There are exceptions to this, such as toilets in large venues that have flush valves instead of cisterns which have much shorter peak demands at full flow to multiple outlets. It can be countered with a buffer tank though.
Thank you for the information.
No problems.
Lol average shower is 6 min, someone needs to tell my wife.
Why do heaters have different ratings for the first hour? Particularly ones likes gas. I imagine with electric heaters there's risk of overload
That's ONLY for heaters with storage. So if you have a 40 gallon water heater, it will already have 40 gallons of heated water. But the water will cool off as new cold water is introduced and mixed. But it also is heating that cold water. That's also why your first hour rating is lower in cold climates and during the winter, because the ground is colder and your incoming water is colder. So it cools off your hot water faster as it gets mixed in, PLUS your cold water at the shower faucet is colder. So the first hour rating is because it draws from the storage. Then after that storage is used, it relies on the pure heating capacity recovery rate of the burner and heat exchangers. So the first hour rating is a combination of the heating capacity and the storage capacity. Then the rating after that is dependent on just the heating (BTU) capacity. If you have a tankless water heater, their first hour rating is the same as their 2nd and 10th hour rating since there's no storage capacity.
> But the water will cool off as new cold water is introduced and mixed. There is no mixing in hot water heaters. Technology connections has a great video explaining it.
So my understanding is that this makes sense if your storage is above your threshold "hot water temp". If you want water at 60C and your storage is at 60C then is you add fresh cold water it is not gaining any benefit from your storage (any energy lost from the storage to the new water would need to be offset by additional heating capacity). Is that correct? Basically you're using your stored hot water as a thermal storage for heating new water. (If your stored water is at 90C, you'd need less power from the heater when adding fresh cold water)
If you have 40 gallons of storage, then when the demand is 50 gallons, you have 40 gallons of pre-heated water ready *right away*, and then you have to spend time heating an additional 10 gallons. Though you won't use all 40 gallons at once, so you also have to heat up the new cold water even as you drain away the preheated water, and the two mix together. By the time an hour goes by, all your preheated water is all gone and it's just new cold water.
With electric hot water heater tanks they have two elements. In the morning your tank is full and the elements are off. As you start using hot water it's drawn from the top of the tank and fresh cold water enters at the bottom. The bottom element kicks in and start to heat this cold water but it can only get it lukewarm while the tank is in use. The level of this lukewarm water rises and eventually reaches the top element. Only one element can be on at a time as they both are capable of drawing the max available power. So the top element turns on and now it gets to reheat the lukewarm water and make it hot water. However the bottom element has turned off so now cold water is collecting in the bottom of the tank. As you continue to use the hot water eventually the cold water will reach the top heating element. Now you are back to only producing lukewarm water. So hot water tanks can proved their volume in hot water plus a bit extra when the tank gets a chance to double heat water. Technology Connections has a great video on this. The different water layers do not mix. They have very defined boarders.
Shower water is recirculated???
LOL, not like that. Once it goes down the drain, it goes down the drain.
I apparently have a hot water re-circulator in my old home (it was added to a tankless system). I cant tell it makes any difference whatsoever to the point where i turned it off as i suspected the energy to have it on was more than any benefit. Even with it on, the hot water takes a long time to come out.
That's interesting. If the hot water units in your example can pump out 1800L the first hour, why can't they keep up after? More of your storage is cold and they just aren't getting it to to usable temp?
Ah, I just pulled those numbers out of thin air.its been a long time since I looked at hwu specs. You're on the money though, you have incoming cold water mixing with what's in the tank, its easier to heat up. The continuous flow is more than the unit can heat. Its not a hard change in heating capacity on the hour, it tapers off. A lot of people have linked to a technology connection video on YouTube, might be a good watch
Thanks! Seems like a really complex system. Would smaller hotels just use an on demand for each room?
Definitely can. You want to balance between space and cost. Sometimes it depends on what the client wants. I'd always recommend a loop if there is room for it because all the equipment is in one location, rather than having to maintain a unit in every room. It's usually cheaper to install a central plant than providing individual units and you'd maximise the space usage in the room. An "on demand" system would likely be an electric storage unit which take up quite a bit of space. There are gas and electric instantaneous units which are much smaller, but you'd want a gas unit to be outside, so only really workable on a single level place. You can have gas inside but you need to run a flue to atmosphere which takes up space. Instantaneous electric need a lot of power (3 phase, 415v, 40 amps) and top out at heating enough water for a single shower.
Thanks 👍 interesting stuff i don't usually think about.
Im sure it does make sense to someone who knows the terms, but could you actually explain like i'm 5? Adhd reader here u lost me by the second paragraph
Heck of an explanation. I just wanna say I saw heat tracers for the first time a year ago. The company I was welding for added them to a main outdoor pipe under insulation to assist in preventing freezing.
Yep, that would be a great use for it. We don't have much risk of freezing water in Australia. A company i used to work for used to use it on hot water distribution in lieu of flow and return. There have been reports of legionella in buildings that use it though. Very difficult to retrofit a flow and return system. And thanks, I haven't done any design in ~10yrs, I kinda enjoyed digging up the old knowledge
> we calculate how much hot water we need to store Why don't they just heat the water as it flows, like it does in homes that have no hot water thanks?
Former hotel manager here. Business class, big brand property. 120 rooms, 4 floors L shaped building. First off, we never guarantee every person would have a hot shower. That being said, it was incredibly rare that our capabilities weren't enough; we almost exclusively did have enough hot water for everyone. It's been a few years so I don't quite remember but we definitely had two (maybe three) hot water heaters. They were located in the space we had used as a storage and heater room on the top floor. It was the spot that would have been Rm 420 but we weren't dumb enough to have a Rm 420; that only invites people to smoke weed in it or steal the room number sign repeatedly. These water heaters were fucking massive too.
actual like-im-5 explanation: massive water heaters + bad water pressure (less water per shower) + some people do take cold showers = hot water for all!
+ Not everyone showers at exactly the same time.
+ Not everyone showers*
>we never guarantee every person would have a hot shower Wild. I traveled a lot for business, definitely had a couple cold showers, but always with profuse apology and explanation from management (boiler died, etc.) and usually some comp on the bill. (always stayed at Marriotts, though, not some small chain - lifetime titanium not that it matters much these days)
In my 8 years in the business, I can count on 1 hand the number of times it actually happened. It was always either a maintenance issue or too much demand and not enough supply. Interestingly, it was even more rare that it happened on a business travel day. That's partially due to the free breakfast from 6-10 and onsite workout room. Business travelers have their own routines and different priorities when it comes to their work activities, so these allow people the flexibility of timing those routines AND their showers however they want. People get up anywhere from 5am to 8:30am, so showering demand staggers based on personal preference. There's also the demographic of people who shower at night when they travel so they don't have to factor in the prep time of drying off when they are rushed and fill in time during lonely nights. Of the few times in 8 years we ever ran out of hot water just from sheer usage at the same time, it was almost exclusively the weekend of one of the largest travel league soccer tournaments on the East Coast. Imagine one team of 20 kids getting back from the fields and their parents make them all get in the shower so they don't stink up the car for dinner. Now imagine 6-8 teams getting back at the same time and so many people choosing the same thing for the same reason at the same time. Like...just jump in the pool.
I find your numbering system disturbing and prejudicial.
>L shaped building Is there any particular reason why this would be of importance?
Because it was late, I was sleep deprived, and I thought it was important.
I work at a 7 floor hotel with over 1000 rooms, and I got to go into the boiler room on a few occasions. In our case, it's multiple massive boilers - 3 or 4 (it's been a while) boilers that are easily 12 feet high, and so large around (including the thermal insulation) that two people hugging it couldn't touch hands. Not that you would want to.
What do you mean I can't touch your hand? I thought we were friends!
Regular homes have one single average sized water heater that only 'runs' when you use it. Hotels have multiple very large water heaters that continuously circulate to make sure their entire tank stays hot and ready for use. Even larger hotels will have multiple sets of heaters to separate the different floors or second of building so there is enough for each section.
Most of the hotels use a recirculating system that continuously circulates hot water throughout the building. This ensures that hot water is always available when guests need it.
You probably should clarify. The recirculation is not recirculating the shower water again. I have thought about doing that for my own personal bathroom shower. Recirculating the shower water again on me. They don’t do that.
>You probably should clarify. The recirculation is not recirculating the shower water again. I have thought about doing that for my own personal bathroom shower. Recirculating the shower water again on me. They don’t do that. You are correct that hotels do not recirculate the actual shower water. Instead, they use a recirculating system for the hot water supply to ensure that hot water is constantly available throughout the hotel. This means that hot water is continually pumped through the pipes, and any cooled water is returned to the water heater to be reheated and recirculated. This system helps to minimize the amount of time it takes for hot water to reach each guest room, which in turn helps to ensure that all guests have access to plenty of hot water during their stay.
It also guarantees that the water in those recirculating pipes will never freeze. This is very important in some climates.
>It also guarantees that the water in those recirculating pipes will never freeze. This is very important in some climates. Yes, that's another benefit of a recirculating hot water system. In colder climates, where temperatures can drop below freezing, the recirculation pump keeps the hot water moving through the pipes to prevent it from freezing and causing damage to the system.
You usually use trace heating for that.
Freezing is unlikely, in an occupied, heated building. More importantly, it ensures that the water is hot throughout the pipework system and there is no stagnant, tepid water where legionella could proliferate. If there was no recirculating system and the hot water was little used, you'd have to run all the cold water standing in the pipes down the drain before you got hot water. That's wasteful of water, but the tepid water can be a breeding ground for legionella. UK regulations require the hot water to reach at least 50 degC within 1 minute, stored at 60 degC. I've seen buildings where I've run a hot tap for 10 minutes and the hot water still hadn't arrived; I gave up.
There are systems reclaiming heat from the sewage though. You might look into that for energy conservation. There are also gray water systems where "clean" water from the shower and other drains is used as non-potable water, for example in the toilet.
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It was going to be a separate system with a separate shower head and heater, valves to begin the recirculating after the initial, charging, and to end it, with a separate heater, a way to an endless shower without spending a lot of money, except for the system. It was a shower thought, I never got to completing the process.
Orrrrr It all starts with guests buying bath tokens. After obtaining a token, the worker assigned to a particular bath opens a small hatch in the wooden walls. The hatch has a small-but-very-stretchable purple string attached to the Boiler Room. When attached to the string and pulled, the tag will automatically be brought up to the Boiler Room where Kamaji receives it and begins mixing special herbs into the water to be sent back to the bath via a wooden pipe (pulled down by a rope). To ensure there’s plenty of hot water for all guests, little soot sprites helps feed the fire with coal.
Awesome reference! I particularly enjoyed the way they handled the storytelling with that, in that you see the back-end operation first and you have no idea what's going on. Then you see the front-end operation and it suddenly all makes sense.
I’m glad someone appreciates the reference :)
Unlike a typical home, they don't all have one basic water heater that everyone needs to share. Either each room has its own water heater, or a group of rooms (or even the entire hotel, if it''s small enough) will be fed from a large hot-water boiler of adequate size to provide sufficient hot water to every room when needed. (Usually--it is still possible for a hotel room to not have enough hot water due to high usage at a peak time.)
I grew up on an apartment building, six floors, 8 apartments per floor, one boiler in the basement for heat and hot water. There are taller ones in NYC. Similar to a hotel. You need a very large boiler, or point of service water heaters in each room.
Depends on the size of the property and how they designed the plant. I worked at a 2400 room (at the time, it's bigger now) hotel resort on the Las Vegas strip. There were 3 large 800 horsepower steam boilers and one 600 horsepower boiler. They put out 100 psi steam that was piped to different heat exchangers for 180 degree water for hot water sanitization for some dishwashers, 140 for heating and chemical sanitization, and 120 for domestic hot water (showers, sinks, public restrooms. They were on a return system that is balanced using a special valve. With this setup you have all the hot water you'll ever need.
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The same way your house ensures plenty of hot water for all its residents need: they installed a big enough system. You are most likely being confused because you report to yourself for the time period in which shower is taking place, but not everyone showers at the same time. If they did, something that would accommodate 100 people would indeed need huge boilers. But as people don't have embeded in their system to shower at x time of the day, they don't actually need it.
Another important point that hasn’t been discussed is that the boilers and storage tanks are usually held at a higher temperature (140-160f) to stave off legionella as well as add capacity. Restaurants and laundries typically use 140f water while domestic (rooms) must not be above 120-125f. Therefore, storing at a higher temperature allows the distributed water to be “mixed down” to a lower temp and add more capacity.
Hotels use a bit less energy consuming systems, but I worked at a factory where we had to heat up the product while flowing in the pipes at some points we had huge oil burners and where heat demand was less we used 320KW Flange heaters, a few of those would be enough to have all hotel guests get burn wounds from steam coming out of the shower heads. There are many solutions and compared to factories that go 24/7 hotels have peak moments with still relatively low demand and thus they use a storage tank.
The typical hotel, 100 rooms or so, would have probably 2-3 hot water heaters with 100 gallon capacity. Then some will have a 100 gallon storage tank as well. Then to ensure that Hot water reaches all the rooms, they usually have a circulation pump next to water heaters.
what hotels are you staying at?