Hotels in general are super cheap construction. Offensively so in many cases. Like a lot of buildings they’re treated as disposable. PTAC units are cheap and easy so they win. Sure it’s possible to do a central system with individual controls in each room, better efficiency, and improved comfort, but it’s more expensive up front, which isn’t a priority for a building that’s written off in 20 years.
One commonality of central HVAC units in large structures with many rooms, is it rarely works to anyone’s satisfaction.
Forced air systems are very difficult to engineer and maintain a balanced airflow with expensive and unreliable duct dampers. Liquid systems suffer the same control and reliability issues with yet even more expensive proportioning valves on the fluid side, not to mention the requirement for individual area air handlers.
Not that central cannot be done properly in this circumstance, but it isn’t “easy”. It requires a huge up front investment in engineering, construction, and short/long term maintenance that PTACs don’t require… Something that most Hoteliers and lessors aren’t interested in.
ninja’d:(
Can you provide a cite (post 1960) that describes a variable 4 pipe system to the same heat exchanger?
But when you close the vent in one room, all the other rooms get more air. And when you close the vent in most rooms, someone wakes up in the middle of the night with a hurricane of cold air blowing out of the vent.
Also, at present, small AC systems are incredibly cheap. They are commodity items. Yes, a custom build can be better, but you can pick up single room split-system units at Costco.
I’m pretty sure that in a hotel situation (as with an apartment) you can’t mix the air between rooms. Any air returned from a room must either go back to that room or be exhausted. I don’t think it can even vent into the hallway for smoke/fire purposes, and if it can, fire dampers are very expensive. So all the discussion about dampers and airflow controls are mostly moot. You could theoretically provide all rooms with ducted air, but it would have to be 100% outside air that’s conditioned before being sent to the rooms ($$$) then all dumped outside afterwards (more $$$). Plus hotels usually don’t have ceilings high enough for all this ductwork.
What usually happens if a hotel doesn’t use PTACs is they have a central makeup air supply for the building. This provides conditioned and filtered outdoor air to each unit, enough to satisfy the code-required number of air changes per hour (this would be only 10% to 20% at most of the amount of air movement from a normal forced air system) that’s then exhausted through the bathroom vents. This all requires much less ductwork, even if it’s supplying all the conditioned air to the hallways and common areas. Each room then has a fan-coil unit tucked away near the bathroom somewhere connected to a central boiler and chiller, most likely a 2-pipe system so it’s either heating or cooling. Some controls on the temperature of the makeup air can mitigate issues with the need for heating versus cooling in moderate spring/fall conditions.
Hotels that have fan-coils under the windows in each room can get their makeup air directly through the wall, and they can also dump their a/c condensation out that way too. This removes the ducted supplies, but it’s harder to control makeup air flow and conditioning. I’ve also been in hotels that have heat pumps in each unit with air supplies and returns in the wall by the bathroom. In that case the makeup air would be plugged into that so you don’t see a separate grille. I wasn’t able to figure out if each room had its own outdoor condenser on the roof, if a couple rooms shared a condenser (a mini-split system), or if there was a central glycol loop connected to a cooling tower and boiler that each room’s heat pump tapped into. There’s many possibilities.
I don’t think you’d see a 4-pipe system in anything but a high rise though. They’re so expensive because not only do you need so much piping, which is almost certainly going to be copper, they all have to be well insulated, and each fan-coil unit requires two control valves and four shutoff valves. Plus it’s a ton of extra parts and pieces to maintain, on top of the issues of running large central systems.
This is a common problem with hotels and other buildings that have a central hot water supply. Early in the morning when everyone is taking showers it can be difficult to get luke warm water, a little later on it comes out scalding. Even maintaining local water pressure can have this problem.
Big difference between “hotel” as in 20 story building downtown, 5 story steel-framed masonry-covered building in the 'burbs, or 3 story stucco-over-woodframe construction near an interstate off-ramp. Likewise 1950s construction versus 2010 construction. Plus of course the big difference in expectation when you (or your employer) are paying $300/night vs. $29.99 plus tax including free “breakfast”.
I wonder which kind the OP meant?
Nicely appointed modern rooms in real hotels have powerful individual controls which can produce truly hot or cold air and significant temperature ranges. I can’t say whether these are thermally provisioned centrally or are in-wall individual units or perhaps a mix of both. I bet there’s a lot of central chiller plumbed to individual heat exchanger plus individual electric heat.
Crappy older big hotels can produce slightly warmer or cooler air (but not both). IOW, crappy low-volume low-leverage heat-or-cool-only “central HVAC” in the worst tradition of office buildings. Individual units range from lots of noise and little temperature change to little noise and lots of temperature change.
No, but who mentioned that? Every 4 pipe system I’ve seen has had separate heating and cooling coils.
Many hotels do have central HVAC systems. In fact, there are HVAC systems that interface with the hotel reservation system that, for large hotels, can save a ton of money.
The way it works is the room has temp controls. These controls allow air in from the central HVAC system. The controls also have an interface to the reservation system.
Check in the room, it sends a message to the HVAC system that the room is now occupied and the room turns on the air. Upon checkout, the opposite happens so you aren’t heating/cooling an unoccupied room. The guest can change the temp in the room and the HVAC/reservation systems note the change and remember it for next time the guest checks in.
I built a hotel/casino computer systems at one point. Before I left I was pushing the AC system quite hard. Would have saved tons of money and also allowed some marketing flunky to make a big deal out of it. Not sure if it happened, I left for a different job.
Slee
Why have separate coils when you can achieve the same thing with a single coil and two extra valves on the return piping? I would think the valves are less expensive than a whole other coil, and the piping isn’t any more complicated, but you’re doubling your chances of a bad valve causing problems. Is it just not worth the trouble, unless of course you’re super space-constrained?
Refrigerant flow systems have major issues. A leak in a system with a lot of pipe can be a major issue. Also with the new gasses alarms and evacuation systems would also be required.
A 4 pipe system normally does not use the same heat exchanger. That is only done on 2 and 3 pipe systems.
And a failure of your control valves could cross hot water into the chilled water system. And you would need 4 control valves. One on each inlet and each outlet. So with 4 valves per unit more chances of a failure. And the piping would be more complicated. And the room coils are not that big and the builder does not care about how much room the maintenance department has to make any repairs.
That would not remotely be enough to make things comfortable. You don’t even have temperature control. And if they don’t keep on both the a/c and heat, it won’t work.
We had something similar in my dorm in college- some kind of centralized cooling water system (think it might have been campus-wide even), but with local thermostats per room to regulate the temperature. I think they may have done the heating the same way- at any rate, it was the same thermostat that controlled both.
But all that’s assuming that the dorm was predominantly full, and that classrooms/offices throughout the campus were mostly in use as well. Hotels can’t rely on that kind of steady usage, so they might well be paying a lot of money to cool the place down.
[QUOTE=sleestak]
Many hotels do have central HVAC systems. In fact, there are HVAC systems that interface with the hotel reservation system that, for large hotels, can save a ton of money.
The way it works is the room has temp controls. These controls allow air in from the central HVAC system. The controls also have an interface to the reservation system.
Check in the room, it sends a message to the HVAC system that the room is now occupied and the room turns on the air. Upon checkout, the opposite happens so you aren’t heating/cooling an unoccupied room. The guest can change the temp in the room and the HVAC/reservation systems note the change and remember it for next time the guest checks in.
[/QUOTE]
Great idea in concept, but if poorly executed, you’ll be better off giving guests a block of ice and telling them to sit on it. A friend is a stationary engineer at a locally well known historic hotel/resort and the guest room HVAC is tied to the bookings. Guest complaints about the HVAC consume a significant part of his time. The old system of having housekeepers do a manual setback worked better from the guests’ perspective as the room would be at worst, 75-78 rather than 80+ with the HVAC completely off.
When his predecessors installed all the “Golly, look at how green we are!” tech, they failed to address the building envelope. Big leaky single-glazed floor to ceiling windows make for a huge passive solar gain on the south side of the building, so if a guest doesn’t check in until the evening, the room has been baking all day. The system can’t cool the room in the short time it takes for a guest to get from the front desk to the room, so the usual reflex is to shove the stat all the way to the “I’m a polar bear” end and eventually the room cools and the guest wakes up shivering. Doesn’t exactly do wonders for the reviews.
After 40+ years I still do not understand why a person who knew how to turn a stat up can not figure how to turn it down, and the person who knew how to turn the stat down can not figure how to turn it up.
I do not know how many stats I found pushed completely one way extreme heat or cold and the tenant complaining about the stat responding to where they set it.
So you can understand the trials of a stationary Engineer working in a hotel I have a story. Or well an example of the trials.
The hotel had a central plant providing hot and cold water for HVAC. The room had a small air handler with controls in the room. The stat had a lever with H and C one each side, and a switch to turn the fan on. I have gotten several calls that the AC is not working. When I get to the room 1st thing I check is the stat. So I have my back to the customer look at the stat and see the fan switch off. I turn it on hear the fan start. then I have to gather my self up put on a completely neutral face turn around and tell the guest that everything is ok and the AC should work this switch here on the bottom of the stat was only turned off. And please call if there is any other problems I will be glad to come to their room.
Try doing that with a straight face.
Back in Ye Olden Tymes thermostats were pretty simple: one on/off slider, maybe one fan auto/on slider, and a lever or knob to set the desired temp. With or without any kind of temp markings.
You deal with one set of thermostats every day. I deal with a different kind every night and 15 different kinds every month. The variety of features, controls, displays, etc., these days is bewildering. And since all this stuff is made for international sales, icons have replaced English. Worse yet, as I’ve gotten older the printing has gotten smaller and the lighting dimmer. Failing to correctly operate what ought to be a simple device is more understandable than you may think. Particularly with systems including time delays.
I’ve gotten to rooms with the AC running when I wanted heat. So I switch to heat and nothing happens. The fan quits but that’s it. 5 minutes later I call downstairs for help and 3 minutes later the heat starts. A further 5 minutes later the tech shows up, calls me a fool under his breath, and leaves. Of course being a good citizen I’d called back to the front desk awhile ago to cancel the request for help. Which never got relayed.
Another peeve I encounter a lot is the maid staff turns the AC down to min temp while they’re cleaning & making up the room. Why? Because they’re running around like crazy working hard and it’s warm. So they put the lever full cold while they’re working so it keeps running including with max fan speed. Then they leave that room to go to the next, forgetting (or not bothering) to reset the thermostat.
10 hours later I check in late the evening, needing to go to sleep promptly to get up early the next day. And … I get up to a room cooled to 64 degrees. With cold-soaked furniture. Of course at that time of year the central heat source is off and the windows don’t open. I have slept in my long underwear and gym clothes including sweatshirt under both beds’-worth of blankets and comforters in Phoenix in August when they had no replacement rooms. Pisses me off no end.
As more thermostats become centrally controlled by the building’s “smarts” there’s some hope this issue will be automated away. OTOH, automation giveth and automation taketh away …
My other least favorite innovation is the “smart thermostat” that won’t run the air handler unless I’m in the room. Saves them plenty of money but leaves me coming back to sleep in a room that baked or froze all day depending on the season and which way the room faces. Color this customer not happy. Not happy at all.
If this is the way you are made to fill or what is happening to you then you have the right to be unhappy.
If you make a mistake I will never laugh unless I have made the same mistake. I am laughing at you and me and the reassurance you are giving me.
Never have I thought a customer who did not turn on a switch that was really in plane sight was a fool. If I did then I am a fool as well because of my mistakes. Yes when I know that you will not be offended I will smile and maybe joke about it, but if my actions ever offended someone for doing something that I have done then I am truly sorry. That is why I took time to put on my game face I was worried about the customer not the company.