Portable air conditioners, sometimes called spot coolers, are most often associated with emergency cooling in heat waves. But portable units can actually provide flexible year-round solutions to a wide range of cooling challenges in high-rise buildings – from emergency use, to planned temporary cooling, to long-term supplemental cooling of critical areas.
Though the applications are nearly unlimited, the “big three” for high-rise facilities are:
- Failure of the central chiller: A chiller system can fail for many reasons, including something as small as a punctured water line. This scenario can knock out the central a/c system for anywhere from a couple of days to a couple of weeks. Portable air conditioners provide emergency backup to keep tenants as cool as possible until the regular system is back online.
- Scheduled maintenance or renovation work: When chillers, air handlers or other components are shut down for planned maintenance, portable air conditioning is the best and often the only way to fill the gap. Sometimes air handling equipment can be serviced over a weekend or holiday period, when occupancy is low and temporary cooling requirements are minimized. If building air handlers are being replaced or refurbished, portables can maintain comfortable temperatures while work is in progress. One common approach is to repair or replace the air handlers one floor at a time. The portable cooling units can easily be moved from floor to floor as work progresses.
- Focused cooling of “hot spots”: Depending on their location in the building, offices, conference rooms or other spaces may be under-served by the central HVAC system and will need supplemental cooling. This situation occurs most often in older buildings, but it can happen anywhere – for example, in a sunny corner office where heat gain is high.
Data centers, server rooms and equipment rooms are also hot spots, because they tend to be densely packed with heat-generating equipment. Portable air conditioners can deliver the needed supplemental cooling on a temporary or ongoing basis, often at a much lower cost than permanently installed HVAC equipment.
For example, in a New York City building, the building a/c system was not providing adequate cooling to a server room operated by a technology company. They investigated using a permanently installed system for supplemental cooling, but found that a portable 5-ton cooler could do the same job for under $10,000 – only a fraction of the $40,000+ estimates received for permanent solutions.
In critical applications, portable coolers also provide redundancy if the central system should fail. A portable unit in a server room can be programmed to kick in at a given temperature set point, ensuring that electronic equipment will remain functional and will not be damaged by overheating.
Types of equipment available:
- Air-cooled portable air conditioners work by exhausting hot air out through ductwork. Air-cooled portables are the most common system of choice because they can be installed almost anywhere, usually in minutes.
- Water-cooled portable air conditioners connect to an external water source. They are very efficient to operate but are limited to use in facilities where it is possible to tap into a central cooling tower or chiller system, or in regions where the municipal water supply is plentiful and economical.
Product offerings were once limited to small 1- and 2-ton units, but the choices have expanded dramatically. Facility managers can now select from a wide range of portable coolers from 1-5 tons in capacity, as well as units as large as 12 tons that are still compact enough to roll through a standard doorway. The supersized units are gaining popularity for use in large server or equipment rooms, where a single cooler can do the job of several.
Avoid the small portable coolers that are sold by home improvement retailers. These units are designed for use in homes and do not have the capacity or durability to stand up to the demands of commercial use.
Proper selection starts with portable equipment sizing, defined as cooling capacity in BTU/hr or tonnage (12,000 BTU = 1 ton of cooling). Basic mathematical formulas may be used to size portable coolers for general applications and for server rooms, but heat load factors unique to the application must be taken into account.
Other considerations to review with your portable cooling supplier include:
- Will the unit be located inside or outside the space to be cooled? Inside is simpler, but if the portable cooling must be located outside the room due to space constraints or other concerns, you will need to find a way to get the return and cold air supply in.
- How will the warm air be vented out of the space? Often it can be vented into the return air plenum for the building, but if there is a tightly constructed ceiling with firewalls, your portable cooling supplier may need to devise another solution.
- Will the portable unit use a single-duct or two-duct system? Single-duct installations are common for emergency or temporary cooling; but in more permanent applications a second duct is sometimes added for greater efficiency.
For example, if you are cooling an office suite in a building that uses night/weekend temperature setback, you can use a condenser plenum on the unit with an additional duct so there will be two ducts going to the drop ceiling, creating a closed-loop system that enables you to cool the space independently. The system will pay for itself quickly through energy cost savings.
- How will condensate water be removed? Choices include a standard condensate tank or bucket, or running a drain line from the unit to an external location.
- Is it better to rent or own? The answer to this question will usually be self-evident; but when in doubt, your equipment supplier can help perform a quick cost analysis to determine the best approach. Even if the equipment is going to be used long-term, renting might make more sense if you want to avoid capital expenditures or if you anticipate a change in cooling requirements down the road.