It seems most hotels I stay at have a noisy heater/AC unit. Why don’t they have central HVAC systems? Don’t most office buildings have them?
Because then it would very difficult for each room to control its own temperature separately
They don’t like to heat/cool unoccupied rooms. With the PTAC units used in a lot of the motels, they can turn them off if the rooms are not going to be used for a while and only run them when they are receiving the income from the room to pay for it.
It also can simplify the maintenance. Your typical motel maintenance man isn’t going to be able to do much if the HVAC system is on the fritz, but he can replace the PTAC unit.
Finally, there is reliability. Again, although the HAVC system rarely has problems, when it does, it can take a day or two to fix. That would affect the whole hotel. The hotel can store spare PTAC units and have a maintenance man swap one out if one should go bad.
Plus, what **USCDvier **said.
Another reason is fire safety: ductwork provides a conduit for smoke — and possibly flame — to travel from room to room, vastly complicating the task of keeping the fire contained.
(While an HVAC system wasn’t directly implicated in the death toll from the MGM Grand fire, I recall seeing more and more individual systems after that incident.)
It can be useful for stashing money, though, if a bunch of people are trying to kill you.
Incidentally, I stayed in a hotel recently that did have central AC. The room just had a knob with three settings which were basically “how much cold do you want pumped in”.
Why would it make it harder to control rooms individually? Just have vents in each room that can be opened or closed. If the room is vacant, close the vent entirely. If it’s occupied but the occupant only wants a little bit of AC, then open it only a little bit, and so on.
Maintainability and fire safety are both issues, too, but those shouldn’t be any different between a hotel and an office building, which do usually have central HVAC.
I work in a 3 year old building with central heat and air. They are constantly fiddling with it. No one ever seems happy. If they had provided closable vents as Chronos suggests (and I actually pleaded for while it was being built – but that was too late of course), things would be a lot easier. In my previous building at least the vents were along the floor and when it was much too cold in the summer, I covered about 90% of the vent area in my office with books and journals.
Except in your office building, the company is paying you to be there, so if the temperature’s a little too cold because a valve is stuck somewhere, they can pretty much tell you to suck it up, buttercup, maintenance will track it down and get the parts in sometime this week. The hotel can’t do that; it has to be fixed NOW or they’ll have to credit/prorate/discount the income from the room. Not to mention such a problem is likely to affect a whole block of rooms, or half the building.
Hundreds of individual systems is probably far less efficient and more expensive energy-wise, but probably far less financial risk and impact due to malfunction or maintenance.
I’ve stayed at a few places like that and apartments that had such a system. It sucks. Upper floors are way too hot, full window opening in January during a cold front type of hot, lower floors colder than you would like. It also negates any on-demand heating/cooling one may want.
So you make the vents directly controlled by the occupant. It’s an incredibly simple system that’s almost impossible to break. That’s what my mom’s house has, for instance, and in over a century the vents have never once needed to be replaced
There are lots of intermediate solutions possible. Single room aircon is not exactly efficient. The old in-wall air-conditioners were pretty dreadful, and noisy. My childhood memories of those was of motels in odd places when on holiday with my family. A more modern split system is better. But still a significant way short of the efficiency that a large central aircon with a nice big evaporating tower on the roof can achieve. Those systems can pump chilled brine or refrigerant around the building, and individual air handlers can be attached to the supply of coolant. In principle each room can have its own air handler, and only drive air and coolant through it when needed. And then only as much as the occupant wants (both cool and air.) It gets messy when what is wanted is warm air. Electric heat is one option, but the energy efficiency for that is not exactly brilliant.
The problem I see is on a central system that has to respond to 100% occupancy to perhaps 10% and still be efficient, at least more efficient than individual controls per room.
I am not in any relevant profession, but my immediate thought is that hotel guests like to be spoiled, particularly in fancy hotels. Given that some people like their accommodations quite warm and others like it quite cool, i am dubious you could keep everyone happy in a large hotel with just vents off a central HVAC.
Hotel service and office building service are two different animals.
I will start with Hotels.
Size is a question. Maintenance staff is another. how many what hours and qualifications.
If you go with the small self contained units then the only thing the maintenance staff has to do is replace a faulty unit, service company can do the repairs.
The hotel guest want to set the temperature of their room according to their comfort. A separate unit in each rooms makes this possible.
A central air unit will limit this. Because the air handle has to both heat or cool the room just shutting of the vents does not work. The rooms are supplied with at least a cold deck air supply. And the temperature of the cold deck is not constant. It can vary from 55 to 70 degrees depending on outside temperature. The heat is supplied either from reheat coils, electrical or hedonic, or by a hot deck supply air. The hot deck air tem can vary between 80 and 120 degrees depending on the outside air temp. But if the sun in on one side of the building and a cold wind blowing on the other then some times it is hard to make everyone happy with what the central air will be able to do. You can get complaints that “I am getting too much hot air blowing on me” at the same time the room is only 65 degrees. If stat is turned down then the complaint is I am too cold. In this system the fire danger is taken care of by installing smoke and fire dampers tied to the fire alarm system like the office building, but with more dampers.
With the guest controlling both the temperature and turning the fan on and off it eliminates complaints. The hotel chooses self contained units for this control
Or if the Hotel is larger and can afford to pay to have a qualified employee then they can save operating cost and give better service by going with a central plant with air handlers for each room. the central plant provides chilled water and hot water for heating and cooling. Problem here is the central plant monitored 24/7.
Office Building.
There are three types.
Owner occupied.
Multi Tenant
And Single Tenant (the white elephant)
Owner occupied owner sets building standards. My last owner occupied Heating to maintain at least 68 degrees cooling 75 degrees. We set the stats to 72 degrees. If the system maintained between 68 and 75 complaints were responded with “your stat is set at 72 degrees but the range is 68 to 75 you are at full cooling or heating now and the system is working as hard as it can to maintain temp sorry there is nothing I can do.” System was badly designed building laid out North South, Heating load was East West. One side of the building was over loaded with a heating load and sunny to it was hot and opposite side of building had little heat load and was cold.
Multi Tenant
Landlord set building standards in leases. If system was maintain building standard with in 0.5 degrees of set point we did not change it. If we could not maintain standard in area and it was building fault then we had to fix it. But if it was due to tenant being cheap during tenant improvement and not putting in proper HVAC vents then they had to live with it. Several time I had to get bids on making improvements to tenant space only to have the tenant reject doing the improvements.
Single tenant (white elephant)
Where does a elephant sleep any where it wants.
If the tenants employee’s complaint reached the right level in his organization then correcting it became a priority. It got fixed or a correction was suggested and worked out between the owner and the tenant.
As to the blocking off vents. That creates many other problems.
A space is designed with air flow balanced. Closing one vent can cause another vent to receive too much air. Or when the temperature changes deprive the space with the air it needs. I have had tenants want me to close the vent over their desk because they were cold and getting too much cold air. Then as the day gets hotter or later in the week they complain they are hot. Or if the day turns cold they complain they are cold.
As Snnipe describes, most HVAC systems are essentially binary, either On or Off and either Hot or Cold. You can get a combination by having the system always blowing cold air and using reheat coils where needed, but then you are getting pretty complex.
In an extreme case, imagine a hotel with two occupied rooms, one which wants the room 88F and the other who wants the room 65F. Not only is the system going to have trouble maintaining both, you’ve got 99% of your output blowing against closed dampers.
Especially since in every office where I ever worked a substantial number of people have space heaters, usually just because they like it warmer than the central heat is set.
Tenants don’t like it when they are told that they have to remove the space heater. I had to ask one tenant if he would like to discuss it with the fire marshal/ Management ended calling the fire marshal to explain why he was not going to se extension cords or space heaters. The tenant final understood after the marshal handed him his violation slip with the understanding if the fire marshal returned and found any more violations he would close his office.
A plot point in the movie No Country for Old Men—and presumably the novel as well, though I’ve never read it—relies on a motel having a central ventilation system. But the motel in the story was not a particularly fancy one. (Also, it’s fictional.)
It is not impossible or hard to do. A 4 pipe system can easily provide either heating or cooling to a space. This required both a chiller and a boiler operating, but the amount of individual zone control is very good.
However, with new construction, I’d expect variable refrigerant flow systems to become more and more common in small to mid-side hotels. While PTACs have their advantages, they are noisy, which is an issue in a hotel.