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        riddles >> microsoft >> Hotel Hot Water
        
(Message started by: TheBean on Jul 28^th, 2002, 10:07pm)

Title: Hotel Hot Water
Post by TheBean on Jul 28^th, 2002, 10:07pm

I'm guessing that the reason hot water is instantly available in most hotels is that it's nearly constantly in use by someone and is therefore circulating in the system to a greater extent. Of course, many modern buildings also have recirculating HW systems to make the hot water appear quickly as well.

Title: Re: Hotel Hot Water
Post by Franklinstein on Jul 31^st, 2002, 5:25pm

I always figured it was the hotel staff turns up the hot water main and turns down the cold water main so as to scald the patrons, kind of a pre-revenge for the disgusting mess people always leave behind.

Title: Re: Hotel Hot Water
Post by Rhaokarr on Aug 2^nd, 2002, 9:16pm

I can state with certainty that there are hotels out there that do not have 'instant' hot water. I've been in my share of hotels where the red-coloured tap is both sluggish and merely warm...

Title: Re: Hotel Hot Water
Post by Dave on Aug 5^th, 2002, 7:16pm

Of course, ifyou turn on the "C" tap in some French hotels, you MAY get scalded! The "C" stands for chaud - French for HOT!

Title: Re: Hotel Hot Water
Post by Robert Grimsley on Aug 23^rd, 2002, 1:57pm

I once lived somewhere where the electric utility charged much more for 'instant hot-water' appliances. Don't know any of the details, but hotels may use similar technology. Of course the constant circulation aspect is there as well.

Title: Re: Hotel Hot Water
Post by Danny W Newton on Aug 26^th, 2002, 4:24pm

Umm...not to escape the obvious...but the reason hot water starts flowing immediately...is because you just opened a valve.

Title: Re: Hotel Hot Water
Post by jeremiahsmith on Aug 27^th, 2002, 1:18pm

on 08/26/02 at 16:24:05, Danny W Newton wrote:

Umm...not to escape the obvious...but the reason hot water starts flowing immediately...is because you just opened a valve.

But why is it hot the second it comes out? It takes a little bit for the water to get warm. Sure, the water comes out when you open the valve, but normally it's cool water.

Title: Hotel Hot Water
Post by Mark in Brazil on Sep 3^rd, 2002, 5:25pm

OK... I've been thinking about this one and I haven't reached a conclusion yet... I'd love to hear what people think of my reasoning to this point, and if anyone knows what kind of approach the creator of the question intended for us to take, please post here to let us all know.

First, we could imagine that each room has its own hot water heater/tank. And unlike in a house, the hot water really only needs to be in one place: the one bathroom the hotel room has. In a house, there is almost always a kitchen and a bathroom and many houses have multiple bathrooms, so hot water in a house normally has to be distributed to multiple places (taps in different rooms). A central hot water heater makes sense for economic reasons (it is too expensive to buy multiple heaters when one can do the job, plus a single large heater can be cheaper to operate than multiple smaller ones... see below), but for the water to get to the hot water tap farthest from the heater can take a bit of time, so you would usually get some cold water coming out before the hot started.

Now in a hotel, why would they have a water heater for each room? They might, for example, have one per floor, or even more than one if the floor is large. It might not make much sense to have a single central water heater for the whole hotel-- imagine a hotel with 20 floors. If the water heater is, say, on the roof or something, it could take a while for hot water to get down to the lowest rooms. If the hot water heater is in the basement, it could take a while for hot water to get up to the highest floors.

One line of thinking on this is an economic one. I'm guessing that the water will lose heat proportionally to the surface area of the tank in which it is stored (or at least of that part that is filled plus the surface of the water). But the volume of water you can store (and the amount of heat you can store in it) goes up like the cube of the typical linear dimension of your water tank (or the filled part), while the surface area goes up like the square. So the percentage of the stored heat you lose in a given time probably goes like 1 divided by the typical linear dimension (loss/heat stored ~1/x where x scales like the cube root of the volume of the tank). This means that in economic terms, it might be better to have a larger central tank, because proportionally less of the energy you put into heating the water is lost in a bigger tank. So hotels are probably interested in the service level (shortness of delay time before hot water comes out) more than the economics of heating the water. That surprises me a bit, because I believe the hotel business is pretty competitive.

Hmmmm... or it may be that even with insulated pipes, the water just couldn't stay hot enough for the people farthest from a single water heater, even if the water were scalding hot for the people closest to the heater.

It is common for bathrooms in adjacent rooms to be next to each other. This is probably to facilitate plumbing. The drains from both (or all) bathrooms can use the same path down. Similarly, the bathrooms can also share a path for the water coming in, whether already hot from a central heater tank or not yet heated from a pipe, to be heated by a heater next to the bathroom.

Does anybody know what kind of approach the creator of this question (M$?) intended for the respondent to take?

--Mark

Title: Re: Hotel Hot Water
Post by Igor on Sep 16^th, 2002, 7:33pm

I'm pretty sure that most large hot water installations use a central boiler that circulates hot steam through the building (which is used both for heating and hot water). The steam pipe could run up to the bathroom, and heat up the cold water through a heat exchanger. Thus, you would not have to circulate the warm water through lossy pipes, but rather very hot steam (it doesn't really matter if it loses a few degrees when it circulates). Of course, it depends on how large the hotel is, because it would not make sense to do that in a relatively small one where the hot water isn't used constantly.

Title: Re: Hotel Hot Water
Post by David Madison on Sep 18^th, 2002, 5:40pm

It has nothing to do with how far away the hot water storage is.

Each room is connected to the hot water storage through a series of pipes, many of which are shared. The heater may be 20 floors away, but that doesn't mean you have one pipe from your room to the heater. Instead you have a short length of pipe that connects with the rooms next to you, which connect to the rooms next to them, etc..

Water in hot water pipes will cool off when standing. But if your neighbors are running hot water at some point, then all the pipes from the heater to your neighbors room will be hot with hot water inside.

So it might just be the usage on the 'tree of plumbing' that keeps it hot enough that you only have to warm up your sections of pipe. And keeping that pipe insulated may help alleviate cooling problems.

You could even design the plumbing to minimize the distance of single-use pipes (exercise left to reader) though I have a feeling you'd have to much running water noise to contend with.

The heat exchange point might be the real answer though, if a steam heat exchange would heat the water near the tap, then your problem is solved, because the steam would always flow, whether the water was flowing or not.

Title: Re: Hotel Hot Water
Post by Thomas on Nov 10^th, 2002, 12:07pm

If you think about the design of most hotels they are mirror imaged rooms backed to i dentical rooms. This leaves 4 bathrooms in on small space. So if you had seperate water heaters that would make sence but it's obviously not the case b/c there is no where to store the water heater. You can't just put it in the wall b/c it might need matinence. I think there is no real answer to theis questions b/c it depends on what type of heating system you use and what type of floor design because all hotels are different.

Title: Re: Hotel Hot Water
Post by James Fingas on Nov 11^th, 2002, 9:02am

Duh ... The reason is that hotels buy special Stay-Hot^TM water, that takes 8 times longer to cool off than regular water.

You guys have some pretty weird ideas sometimes!

Title: Re: Hotel Hot Water
Post by TimMann on Nov 11^th, 2002, 7:19pm

I think David Madison's "tree of pipes" explanation is right. I claim to be qualified on this because my dad was a plumber. :) (I'm not serious about that -- he was a plumber, but I never asked him this question, so I don't have the benefit of his opinion.)

Anyway, if this is true, if you get up at 4:00am on a cold day and take a shower, you're fairly likely to find that the water is not instantly hot, and in fact takes quite a while to get hot. You might still get lucky and be close to the water heater, but if you're far away there are a lot of pipes to heat up in between, which your later-rising neighbors have not already taken care of for you.

If memory serves, I've experienced this phenomenon once or twice when I had a very early flight to catch.

Title: Re: Hotel Hot Water
Post by 73 Hands on Nov 12^th, 2002, 2:01am

Hey Guys,
Hotels are normally built in some sort of circular fashion wherein the water from the heater could be circulating from one side to the other and around again. through this awesome web of pipes and....other plumbing related things. Keeping this water running would be a small price to pay considering the reputation they might recieve.

On the other hand. Believe it or not, I don't normally get this sweet sounding shower-ready water at the hotels that I visit.

Title: Re: Hotel Hot Water
Post by GL ChienFou on Nov 12^th, 2002, 1:57pm

I built my house (which is larger than a small hotel) to have permanent hot water, same as hotels. There's no trick answer it's straight forward. You install one pump for central heating as a matter of course, don't you, and the water flows round a closed circuit. Same for instant hot water. Run pipes from the hot water storage round the building in a closed circuit, and pump the water round. Wherever you tap off the water it will be hot as soon as you've flushed the small quantity of standing water from the spur leading to the tap (faucet). I have 7 outlets and instant hot water.

If you do it with wide bore pipes you can arrange it to work just from convection but it's not as good.

Title: Re: Hotel Hot Water
Post by Martin S Taylor on Nov 14^th, 2002, 1:32am

on 08/05/02 at 19:16:42, Dave wrote:

Of course, if you turn on the "C" tap in some French hotels, you MAY get scalded!

Unlikely. In my experience French taps are labelled 'C' and 'F', which appear to stand for 'Cold' and 'Freezing' respectively.

Title: Re: Hotel Hot Water
Post by Kryai on Nov 27^th, 2002, 2:43am

I think also this question involves the meanign of hot water. what is hot itself is very subjective. As i've found from my fiancee's discomfort of my "hot" water. Since the question is applying this to all hotels, and honestly in the last hotel I stayed in it CERTAINLY wasnt coming instantly to where i could shower. However the water they DID label as hot did come out near instantly. So i think that merely saying that if they want to call that hot water then as a previous person stated, that water came out near instantly. Even if that water was a 1 degree Celsius, if that was the hot water, and assuming the plumping was working correctly, then the answer would be much easier.

Title: Re: Hotel Hot Water
Post by M1A1 on Dec 4^th, 2002, 1:59am

on 08/05/02 at 19:16:42, Dave wrote:

Of course, ifyou turn on the "C" tap in some French hotels, you MAY get scalded! The "C" stands for chaud - French for HOT!

Title: Re: Hotel Hot Water
Post by Guest on May 14^th, 2003, 5:23am

well, I'll have to disagree here, since this is not always true. I live in a high rise building (8th floor) and when I turn my hot water it does not instantly come out pouring, it just takes like 5-8 seconds sometimes, so its probably more for low rise buildings and hotels....... :-/

Title: Re: Hotel Hot Water
Post by Eleanor Pickron on Jul 12^th, 2003, 10:31pm

:-* Would anyone consider that in all other places on the planet besides the US, hot water tanks are not used.

Everywhere else, flow-through hot water heaters that are placed in the walls right next to the output spigots; there may be one in a bathroom for instance, which provides hot water for both the sink and the tub. The water is cold in the pipes up to the heater, which is about the size of a medicine chest, and then heated instantly, much like the Mr. Coffee process where you pass cold water over the heating element in the coffee maker.

Now, US citizens would experience this most likely in foreign hotels, but if you have lived in apartments or been a guest in foreign homes, you will have seen the same technology in use in those environments as well.

This is much cheaper and more efficient than all those multi-pipe recirculating solutions.

Kohler even adds one of these heaters to their newest line of hot tubs for sale in the US if you are interested in seeing it, go to a Kohler showroom. I am only adding this as a way to prove what I am saying, not as a plug for Kohler products. :)

Title: Re: Hotel Hot Water
Post by Icarus on Jul 13^th, 2003, 1:00pm

Eleanor - I don't know where you get this "the USA is sooo backward" idea, but it simply is not true. On-demand water heaters are just as available in the US as in other parts of the world. They are not particularly popular here yet since they are limited in the amount of flow they can support (tank water heaters can support any amount of flow, but only for a limited time. In-line water heaters can last any amount of time, but if the flow is too great, your water is only warm). Most hotels - both in the US and in other countries - use steam systems as described in earlier posts because they are cheaper and work better than both tank systems and in-line units, but only for large institutions which use steam for heat distribution anyway.

Even leaving out large hotels and other institutions and their steam systems, your claim that tank systems are used only in the US is obviously a massive exaggeration. You have no idea what is used for heating water in most of the world. In fact, for a large majority of the world's population hot water is only available in pots over fires.

Title: Re: Hotel Hot Water
Post by guest on Jul 26^th, 2003, 11:50am

I think most everyone here is missing the point of this question. The question is why, not how, although most technology minded peoples look at the how first. The correct interview answer for a sales oriented company is 'Because that is what the customer wants.'

Instant hot water in nicer hotels is part of the product they are offering. You don't get instant hot water in your 8th floor apartment because the expense does not justify the return. Would every tenant be willing to pay more in order to avoid waiting for hot water (more competition for short term tenants in a hotel than long term tenants in an apartment building)? And if you were a frequent hotel patron and were used to instant hot water, would you not be unpleasantly surprised if your hotel didn't have instant hot water, even if it were just a minor inconvenience?

The gentleman who has the house larger than a small hotel with the recirculation system for instant hot water should have gotten this. He chose to have instant hot water. The expense was less than his desire. Perhaps his affluence hasn't come as the result of selling a product and therefore he isn't customer oriented.

Always remember that in most cases you wouldn't have a job if not for the customer and even if you don't consider the customer in your everyday work, during an interview you should keep the customer in mind.

Title: Re: Hotel Hot Water
Post by Sir Col on Sep 25^th, 2003, 11:16am

GL ChienFou has described the most common method used in hotels. A continuous loop starts at the hot water tank and runs from room to room, with bypass valves located at each tap, finishing back at the hot water tank. A heat sensor, fitted to the return pipe at the tank, combined with a timer, employs a form of fuzzy logic to operate the circulation pump.

In reply the guests criticism of our interpretation of this problem: hot water circulation systems in hotels are not used primarily for the guests' convenience, but to save money; they reduce water wasted by running the tap before hot water arrives. Hot water on tap, so to speak, is a bonus. This is especially true in cheaper hotels, where instant hot water is only activated, via the timer, during peak times. More expensive hotels, however, would operate the system for longer periods; in this case, it certainly is a luxury with no major cost benefit considerations.

So now you have the how and why. ;)

Title: Re: Hotel Hot Water
Post by Steve on Dec 1^st, 2003, 1:54am

The first thing I thought of when reading this riddle is that the pipes connecting the hot water tap and the heater have some sort of heating coil wrapped around to keep the pipe always hot.

That's how I'd do it anyway .. and make sure I charged well for such an wasteful expense of energy!

Title: Re: Hotel Hot Water
Post by DewiMorgan on Jun 6^th, 2006, 11:47am

I think the Guest, who states "the question is why, not how" has a point.

Not only, as he points out, is it what the cstomer would desire but it also makes economic sense.

Consider the situation where the pipe runs for 30 seconds before passing hot water, with the case where it runs hor water instantly.

30 seconds of flow is about 30 pints, in a reasonable bath tap.

Means 30 pints of cold water is wasted down the plug, which means 30 pints of water more than was needed has been drained from the hot water tank.

If the customer can be given hot water immediately, they will waste less.

Water in piping will indeed lose heat, but this can be used for heating anyway.

Title: Re: Hotel Hot Water
Post by cunninglinguist on Jul 3^rd, 2007, 6:23am

The hotel water management system uses Linux / Dos operarting system which boots up fast and rarely prone to hangups and quirks unlike MS windows!

Title: Re: Hotel Hot Water
Post by Grimbal on Jul 3^rd, 2007, 7:00am

on 07/12/03 at 22:31:21, Eleanor Pickron wrote:

:-* Would anyone consider that in all other places on the planet besides the US, hot water tanks are not used.

I wouldn't. In Geneva, Switzerland, central heating is common. It makes sense that if you already have a central heating system that heats the house by circulating hot water, you might as well use it for producing hot water for the shower.

Title: Re: Hotel Hot Water
Post by tiber13 on Jul 7^th, 2007, 3:00pm

Why dont they have a heater on the roof, and all the hot waterwould floww down, and out through the pipes?

Title: Re: Hotel Hot Water
Post by towr on Jul 8^th, 2007, 8:19am

on 07/07/07 at 15:00:23, tiber13 wrote:

Why dont they have a heater on the roof, and all the hot waterwould floww down, and out through the pipes?

Because it might take 5 minutes before the water gets to the faucet. That would waste a lot of water and inconvenience guests.

Title: Re: Hotel Hot Water
Post by Grimbal on Jul 8^th, 2007, 2:41pm

on 07/07/07 at 15:00:23, tiber13 wrote:

Why dont they have a heater on the roof, and all the hot waterwould floww down, and out through the pipes?

If you mean that the hot water would flow down by itself if the heater is at the top, I think it rather tends to flow up, and only if the pipes are quite wide.

Title: Re: Hotel Hot Water
Post by mrgomgom on Jan 13^th, 2014, 2:20am