Energy Efficiency Is Key to Technologies
This article will define two of the newer technological breakthroughs - modular chillers and chilled beams - and how mechanical contractors can integrate them into their designs for new or replacement HVAC systems.
A modular chiller is a small version of a regular chiller that can be connected in series to additional modular chillers to create a full-size chiller. According to Howard Kelly, communications and marketing director for Multistack, “This type of system provides energy savings and redundancy, which is important when you have any type of critical cooling need.” What is meant by redundancy is simple: If you have a big 300-, 400-, or 500-ton chiller with a single large compressor on it, if the compressor has a problem, the chiller is out of commission. “With modular chillers, two compressors per unit are part of the design, so should one compressor fail, the other is still working. Now factor in an array of ten 50-ton chillers, you have 20 compressors. It would take an awful lot going wrong to leave you without cooling capabilities.”
The application of a modular chiller fits the profile of energy savings based on how it works. Kelly gave an example. “Let’s use a typical office building with a 500-ton peak demand as the basis for discussion,” he said. “The building is designed with a 500-ton chiller that can meet the demands of the building on the hottest day of the year with no problem. The issue arises when you consider that the hottest day of the year happens about one week a year in the heart of the summer. Every other day of the year the load is less than peak.
“To meet the demand of a 500-ton load with modular chillers, we would install ten 50-ton chillers connected together as one. With our control system, we would turn on as many modules as needed to meet the building demand, but more importantly, turn off as many as necessary when the building demand diminishes, for example, early mornings, nights, weekends, spring, fall, etc. By turning modules off, energy savings are instantly realized.”
Modular chillers save on energy use by drawing enough power to run only as many units as needed. But heat disposal must also be a consideration and according to Kelly, a chiller is “nothing more than a heat disposal unit as we really don’t cool things as much as we remove heat from them.”
The traditional commercial building has a separate heating and cooling system that often runs concurrently, using natural gas to run the hot water boiler while running the air conditioning to cool the computer room, as an example. By utilizing a modular chiller as part of a chiller system, the heat that is generated during the cooling phase can be utilized in the building for free. The hot water generated can be directed to supplement or supply the gas boiler, used to do dehumidification control, or even supply heat to areas that need it, while keeping the data center or computer room cool, also for free.
“Modular chillers are not always the answer,” said Kelly. “But when you look at a retrofit application where you have a typical downtown building designed to last 100 years with a chiller designed to last 30 years in the basement, the installation ease of a modular system suddenly makes a lot of sense on top of the energy benefits. Normally to remove that 30-year-old chiller, you would need a city permit to close down a crowded street, a demolition crew to tear up the sidewalk, dig a hole under it, and break through the wall of the building. Then a crane to hoist the chiller out and put a new one in its place.
“A modular chiller can usually fit through an office building door and ride on a freight elevator. That means no crane, no demolition, no closing the street. In fact, it has been done many times where a crew with plasma torches cuts up the old chiller to move it out on the freight elevator while modular chillers are being stacked together to replace the old unit.”
Chilled beam systems are an energy-efficient method of conditioning indoor spaces. The chilled beam itself comes in two variants - active and passive. An active chilled beam incorporates a diffuser with ventilation air (outdoor air for occupants, called primary air) ducted to it and has a water coil in it. Passive chilled beams are a cooling coil in the space with chilled water piped to them.
“This is a high induction diffuser that has the coil in the path of the induced air, such that this induced air passes through the water coil and can be either heated or cooled (by flowing chilled or heated water through the coil) before it mixes with the incoming primary air and is distributed to the space,” said Chris Lowell, managing director, Halton Indoors Americas. “With the passive beam, ventilation air must be handled by another system, and they aren’t typically used for heating (due to stratification).”
Both of these types of beams operate as dry coils (no condensate, no drain pans) and must be designed so that the ventilation air (the primary air to the active chilled beam) can handle the latent load in the space while the chilled beam coil handles the sensible load. “In addition, the quantity of air being introduced needs to be only enough for ventilation rates in the spaces or enough for latent control,” Lowell said. “Furthermore, chilled beams utilize the high heat capacity and efficient pumping of water to transport energy to or from the space (again, an energy savings).”
How can mechanical contractors pass this technology on to their customers? Lowell said that besides the potential for energy savings, new buildings can be built with less interstitial space required since the duct sizes are significantly smaller with the HVAC ducting only distributing the small quantity of ventilation air for occupants. “This can result in shorter buildings, more floors per building, or more space for the mechanical contractor to utilize for other systems,” he said. “Additionally, for existing buildings that are being up-fitted, the small duct sizes and piping that chilled beams require can typically be easily accommodated to convert to a more energy-efficient and more comfortable HVAC system.”
The air-handling unit is usually smaller than an all-air system and the structure/infrastructure can typically support this for up-fitting. A final selling point is occupant comfort, which Lowell said “is excellent with the chilled beam systems, being quiet with the ability to adjust and control for individual comfort and for changes in building spaces where tenants may be changing or changing configurations.”
One final note about chilled beams: When applying them, it is important that the building envelope be energy efficient. “This will significantly impact the first cost of the system through the total amount of chilled beam(s) required as well as the design of the air-handling unit and chiller systems,” Lowell said.
For more information, visit www.multistack.com and www.halton.com.
Publication date: 01/24/2011