Stupid Question About Hi-rise Environments! (tenants, commercial, state, rooms)

[claymoore]

This was a difficult post to figure out where to ask the question!

I have wondered for years (I have no life ...) how this is done?

Those buildings in places like New York with hundreds, if not thousands of offices ... How do they each, regulate their air conditioning?

For instance, If I like 75-degree temps in my office and some other office likes a seventy-degree environment ... how do you regulate it?

Yes, I know about thermostats but a Thousand different offices?

Is there one big unit on the roof?

What if I want eighty degrees which would mean the use of a heating unit in the winter?

At one time I see (from pictures) that every office had wall units?

What changed?

Thank You

[fishbrains]

It depends on the type of HVAC system in the building, and there is an entire industry built around it. Mechanical engineers are the design professionals for this purpose.

Older buildings have radiators, and to quote a popular elementary school phrase, “you get what you get, and you don’t get upset”. This leads to warm rooms, and people open windows in the middle of winter to moderate the temperature. I remember sleeping in my 23rd story NYC apartment in January with all my windows open because it was so hot.

More modern systems have VAV boxes in each room. These allow you to vary the air flow according to demand, dictated by the thermostat. In a simplified way of thinking about this, you turn the thermostat down, more cool air flows into the space.

There are other methods. Chilled beams, radiant heat floors, etc. for the layman, the dental HVAC system will supply heat or cold, and the thermostat will vary the supply of the air (or water) to meet demand.

[NOLA2SGF]

I worked in a high rise building. It had the HVAC on the roof.

We couldn't fiddle with the thermostats; temperature was controlled by the real estate company that owned the building (and leased the suites to the organizations that had offices there). They controlled it remotely from their headquarters 10 miles away, somehow.

[Wells5]

Modern mid and high rise buildings have a "4 pipe" HVAC system. Chilled and hot water from central units are pumped to "air handlers" that have heating and air conditioning coils through which forced air is passed. They are controlled by thermostats in offices or apartments. Cheaper settings have 2 pipe systems.

[jaynarie]

I work in a large high rise (about 1 million square feet)
Some floors are divided into small suites. Some are large open areas full of cubicles. I work in a large open area. There are thermostats every 100 feet or so. Most conference rooms (except super small ones) have their own thermostat. We can only control so much though. Between 72 and 76. Oh, the bathrooms have their own thermostats, too. A/C condensers are on the roof. There is a mechanical closet on each floor. I've never seen inside, as it is locked, but it is related to the HVAC. You can hear the air kick on before it starts blowing.

[claymoore]

Thank You All for your responses.

I must say that I am still 'a little' confused.

Maybe I'll have to move to New York?
Uh No!

[chet everett]

Originally Posted by Wells5

Modern mid and high rise buildings have a "4 pipe" HVAC system. Chilled and hot water from central units are pumped to "air handlers" that have heating and air conditioning coils through which forced air is passed. They are controlled by thermostats in offices or apartments. Cheaper settings have 2 pipe systems.

The limits of systems where "the whole building" is switched over to cooling or heating have been well known for many decades. There were four pipe systems installed in some commercial facilities prior to WWII and they've largely replaced two pipe systems in the recent decades. Very modern digital controls and ultra-high efficiency heating plants have made it somewhat feasible to operate "closed" buildings with a two pipe configuration, but the trend even when that is possible is to at least supply "compact cooling units" to the various spaces in renovations and such.

With things like LEEDS certification and consumer demand for precision control of temperature the trend is to give tenants as much ability to monitor temps / energy.

[jackalope48]

Since I operate a couple I'll try and simply explain.

Simplest is that functionally every several thousand square feet of a large building has it's own a/c unit. In a large building this is an air handler that is linked to a thermostat.

So why don't big buildings have dozens or hundreds of those little boxes outside like houses do? Because that portion of the system is consolidated into a chiller(for cold) or a boiler (for heat) typically sized for an entire building. The water or refrigerant that these units create is then piped to the air handler in every section of the building. At each air handler the machine makes a decision of whether to turn on based on it's thermostat setting and what the thermostat reads as the temperature. It uses the cold water to cool and the hot water to heat

After the water is run through the system it typically is either recycled or goes to a tower where the ambient air temperature heats or cools it back to a normal temperature where it is then disposed of(if chemicals are used in the refrigeration process they are removed before disposal). If you ever notice fountains near large buildings in many cases they are fed by the air conditioning system so the water is not put into the sanitary sewer system. If you see steam coming off the top of a building that's the cooling tower returning water to ambient air temperature.

Modern systems are typically connected to an energy management system which is a computer program that connects to each thermostat and unit in the building including the chiller and boiler. That program allows a building owner or manager to remotely control the system through an internet connection. Most owners allow a certain level of control by tenants through a "set point system". That will typically mean there is a building wide system temperature of say 72 degrees but the system will respond to thermostat inputs within a range of that say 70-76. The system also allows the owner to control when the system turns on and off and to turn off different parts. For instance in Texas we don't use the boiler much but when a cold front comes in we turn it on and the chiller off.

This type of system is not unusual. I have one on a 20,000 sq. ft. office building. Some places where there is a density of large buildings actually have chilled and heated water utilities where the building buys it at a metered rate. For instance my city has one for the convention center, arena, and all the nearby museums.

[fishbrains]

Jackalope has a decent summary. If you want to read up on this, the technical terms are open loop and closed loop.

You can then go down the rabbit hole and read about geothermal systems, types of refrigerants, heat exchangers, the different circuits water circulation, chillers, boilers, etc.

As you can see, there is no single answer as to how buildings are heated/cooled.

The simplest way of thinking about this is that water (typically, might have additives such as propylene glycol) is pumped throughout the building, and the differential between room temp and water temp causes a heat transfer. Hot room, cold water, you cool down. Cold room, hot water, you warm up.

This water can run through floors, ceiling units or radiators, and controlling how much heat is transferred depends on thermostats, fans, flow rates and other mechanisms.

You can often see the guts of this system above the ceiling tiles, or in exposed ceiling areas. Some of those pipes are HVAC water pipes. Others are sprinklers, others might be natural gas. Electrical conduit is also up there, ranging from 1/2” in diameter to 6” in diameter. Add in plumbing for water supply and sanitary sewers, and it is quite a maze up there.

This is the main problem when people talk about tiny houses, or converting shipping containers into homes. People often talk about the cost of the structure, but they don’t include MEP (mechanical/electrical/plumbing), which can add considerable cost.