Introducing A New Concept in Packaged Air Conditioning!

These new big building air conditioning products by Dunham-Bush combine: The benefits of economy, flexibility and compactness offered by Ice-Cel tube-in-tank frozen storage modules and The convenience, reliability and low cost of pre-engineered and factory-packaged chiller systems.

What is an Ice-Cel?

Ice-Cel is a modular ice thermal storage tank. The tank is filled with water, in which is submerged a polyethylene tube heat exchanger. A glycol solution cooled to about 26°F by an air conditioning liquid chiller is pumped through the tubes, causing the surrounding water to freeze. When fully frozen, the Ice-Cel stores 240 ton-hours (844 kWh) of cooling capacity, so, for example, it would require 10 hours operation of a 24 ton (84 kW) chiller to fully freeze the water in the tank.

Then to serve a cooling load, the ice can be melted at a rate dictated by load, ranging from 0 to 36 tons (0 to 127 kW). For example, the Ice-Cel could serve a steady load of 20 tons (70 kW) for 12 hours. In providing cooling, the glycol solution flows from the Ice-Cel to the load device (such as an air handler) at a temperature of 34-38°F.

Dunham-Bush integrated systems are offered on two forms:

Packaged Integrated Systems in the range of 25 to 75 tons (88 to 264 kW) which include a chiller and up to 3 Ice-Cel tanks mounted on a skid with integral microcomputer controls, glycol pump and interconnecting piping. They are available with either air- or water-cooler heat rejection.

Pre-engineered Integrated Systems in the range from 100 to 550 tons (352 to 1934 kW) which consist of a chiller, multiple Ice-Cels, pump and microcomputer controls shipped separately for field assembly into an integrated system. These systems are also available with either air or water cooled heat rejection.


How does an Integrated System Work?

The most common application of an Ice-Cel Integrated System is in large building air conditioning, where it is used to store cooling effect during the night, to be used for air conditioning during the day. It can also be used to serve an intermittent process, where cooling is stored over a long period, to be used in a short period.


Advantages to a building owner of ice thermal storage:

Demand Charge: Most big building utility rates include a heavy demand charge based on peak demand charge based on peak demand, which is usually experienced in summer daytime. Ice-Cel allows some of this peak demand to be shifted to low-demand nighttime periods, thus reducing demand charges for the entire year.

Energy Cost: Many electric utilities offer time-of-day or time-of-use electric rates, where each kWh of electric energy used at night costs less than in the daytime. In some cases, the nighttime rate is less than half the daytime rate. Ice-Cel, by utilizing the chiller at night, takes advantage of this incentive.

Rebates: Many electric utilities offer up-front rebates for equipment that will shift peak loads to off-peak hours. Thermal storage usually qualifies. In some cases, the rebate is large enough to pay for the cost of Ice-Cel tanks.

Colder Air: with Ice-Cel thermal storage, chilled liquid is available at temperatures of 38°F (+3.3°C) or less, rather than the 44 or 45°F (6.6 or 72°C) commonly available from liquid chillers. This lower temperature allows air handling units and ducts to be downsized and air handler fan power to be reduced. The result is colder air distribution and lower room humidity, with lower humidity, a room's thermostat can be set slightly higher for the same comfort level, thus reducing air conditioning load, the net result is reduced installed cost and operating cost.

Standby Cooling Capacity: With Ice-Cel thermal storage, standby cooling capacity is available for peak load periods. So cooling capacity exceeds the instantaneous capacity of the installed chillers. This can be valuable for batch process cooling, where high short-term loads are encountered.

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Installing an Ice-Cel Packaged System

Since the Ice-Cel Packaged System is mounted on a single skid; all it needs is a flat concrete slab capable of carrying the unit operating weight.

Water cooled packages should be installed in an indoor equipment room. The only connections needed are:

1. Piping from unit to building chilled glycol loop.
   If the owner prefers to run chilled water to air conditioning loads,
   a plate heat exchanger can be provided as a special option, to isolate glycol within the package.
2. Three phase electrical connection to unit terminal block.
3. Condensing water piping connection to cooling tower.

Condensing water pump can be provided in the integrated packaged as a special option.

Air cooled Integrated Package Systems should be installed on a slab outdoors. The only connections needed are:

1. Piping from unit building chilled glycol loop.
   If the owner prefers to run chilled water to air conditioning loads, a plate exchanger can be provided as a special option, to isolate glycol within the package.
2. Three phase electrical connection to unit terminal block.
   
   

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Packaged Integrated System advantages

Ice-Cel Packaged Integrated Systems offer the following advantages over field-installed equipment:

1. Per-engineered matched components assure reliable operation.
2. Cost of separate equipment pads and field labor for mounting chiller, pump(s) and ice tanks is eliminated.
3. Cost of separate wiring to chiller and pumps is reduced, since there is one common connection. Pump starter(s) are included in package.
4. No field control wiring to install between components.
5. Cost of field piping between chiller, pump(s) and ice tanks is eliminated.
6. One source responsibility for all major air conditioning equipment.

Installing a Pre-Engineered System

• Since these systems are shipped as separate components, they must be field installed, using the following guidelines:
• Ice-Cel tanks should be installed on a concrete slab capable of supporting the operating weight. They may be installed indoors, outdoors on a slab or buried in the ground.
• Water cooled chillers should be installed in an indoor equipment room.
• Air cooled chillers should be installed outdoors on a slab.
• Pumps should be mounted in an indoor equipment room.
• All interconnecting piping and wiring must be field installed.

Pre-Engineered Integrated System Advantages

• Pre-engineered matched components assure reliable operation.
• Pre-engineered controls take the guesswork out of control logic.
• Modular components afford flexibility in location.
• One source responsibility for all major air conditioning equipment.
  

Operating strategies:


With Full Storage, the Ice-Cel tanks supply enough cooling capacity to meet the maximum expected daily cooling demand, and chiller capacity is provided to replenish the ice during the nighttime recharge period. For example, consider a building with 75 tons (264 kW) maximum cooling demand, operating from 7 a.m. to 7 p.m. with an 80% load factor. The maximum daily cooling demand is 12 hrs. x 75 tons x .80 = 720 ton-hours (2535 kWh). If this is completely furnished by Ice-Cels, it will require 720/240=3 cels. To recharge the Ice-Cels during a 12 hour nighttime period will require chiller capacity of 720/12=60 tons (211 kW). An ACSR-3 Ice-Cel Packaged Integrated System will meet this requirement. The advantage of full storage is that he chiller will not operate during the daytime peak demand period.


With Partial Storage, the liquid chiller is used at night to recharge the Ice-Cel and during the day to supplement the Ice-Cel in serving the air conditioning load. Using the same building example as above, we might choose to use 2 Ice-Cels, with 480 ton-hours (1690 kWh) storage capacity.

Then to recharge the Ice-Cels in 12 hours, we need chiller capacity of 480/12=40 tons (141 kW). An ACSR-3 Ice-Cel Packaged Integrated System will meet this requirement. During the day, this chiller doing air conditioning duty will have abour 64 tons (225 kW) capacity because of higher suction temperature. Daytime chiller demand will be only 35% of its full capacity.

Ice-Cel construction:

The Ice-Cel tank is a double-wire fiberglass tank with two inches (5.1 cm) of urethane foam insulation between the two walls. This insulation is so effective that heat leakage in an 80°F (27°C) room is limited to 0.14 tons (0.5 kW). A removable cover of the same construction is provided. The heat exchanger consists of horizontal rows of serpentine coils of 0.75 in (1.9 cm) OD polyethylene tubes held in a rigid bundle by radial plastic spacer bars.

Each coil of tubes is connected to vertical inlet and outlet headers of the same polyethylene material. Tubes are thermally welded into the headers to form one homogeneous heat exchanger with no fittings or joints to leak. The heat exchange is tested to 250 psig (1724 kPa) and rated for an maximum operating pressure of 150 psig (1034 kPa). The headers have stub outs of PVC pipe for easy connection to external piping.

All metal parts within the Ice-Cel that support the heat exchanger and secure it within the tank are made of corrosion-resistant materials; stainless or zinc- coated steel.

The Ice-Cel design is protected by U.S. Patent 5,109,920 and other patents pending.

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Ice-Cel construction:

Ethylene glycol solutions have been most popular for ice thermal storage systems because of good heat transfer properties and low cost. However, recent EPA regulations regarding the toxic nature of ethylene glycol have made it less desirable to building owners.

Propylene glycol solution, which is non-toxic and therefore avoids EPA regulation, is also acceptable in Ice-Cel systems, providing performance equal to ethylene glycol at somewhat higher pressure drop.

Whichever glycol solution is chosen, it is important that the correct inhibitors be included in the solution, compatible with the materials of typical HVAC systems: copper, steel, brass, and plastic. Uninhibited or automotive glycols are unacceptable in HVAC systems. Dunham-Bush offers either Ethylene or Propylene Glycol specifically formulated and pre-mixed by Dow Chemical Co. for use in Ice-Cel HVAC systems, delivered to the job site.

Ice-Cel construction:

1. Control for both Packaged and Pre-Engineered Integrated Systems is provided by a microcomputer mounted in the chiller control panel. Control functions provided include:
2. Capacity control of chiller to maintain selected leaving chilled liquid temperature.
3. All safety functions to protect the chiller.
4. Dual leaving chilled liquid set points to provide for ice freeze mode and air conditioning mode.
5. Annual calendar scheduling to program for weekends, holidays special events, etc.
6. Daily scheduling to initiate freeze cycle and melt cycle.
7. Provide for partial storage: proportioning of chiller/ Ice-Cel cooling capacity vs. time of day.
8. Operate chiller at full load in freeze mode until brine temperature decreases, then shut down chiller.
9. Start and stop condenser pump on water cooled machines. Control fan staging on air cooled machines.
10. Remote monitoring is available by remote terminal or computer, connected by hard wiring or phone modem.

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