Thermal Energy Storage

On the hottest hour of the hottest day of the year, a building may need 200 tons (about 700 kW) of air conditioning. The rest of the year it will require a lot less cooling. Without a TES battery, the air conditioning system installed must be large enough to provide 200 tons (700 kW) of cooling. If we look at the same building over a 24-hour period, it may only need a total of 1,640 tons (5,768 kW) of air conditioning, an average of only 68 tons (240 kW) of cooling per hour. With Thermal Energy Storage we can theoretically air condition the building on the hottest day using only 68 tons (240 kW) of equipment.

            Insert chart showing peak & average loads

By incorporating complete “system integration” into the building, the same system that cools the building can also heat the building or make hot water using “waste” heat from the refrigeration system.

Ice Storage

As concerns about greenhouse gas emissions increases and fossil fuel costs rise, alternative cooling systems have become more attractive and much more cost-effective.

To understand the effectiveness of ice storage, it is important to understand how a building is used and how it operates. A typical office building is occupied about 10 hours per day. As people arrive at work, lights and computers are activated. An average person radiates the equivalent heat of a 150-watt bulb. The sun begins to warm the east side of the building.

In many large buildings the activities of the occupants and equipment are enough to heat the building. In fact, there is often enough heat produced that air conditioning is required even on very cold winter day. Once the sun sets and the night time temperatures plummet, the building will need heat.

Ice Kube heat pumps are designed to operate efficiently at temperatures low enough to make ice, to cool the building during the day. While the pumps are making ice, hot water is produced to warm the building at night.

Significant Savings

TES reduces the amount of equipment needed to cool the building by as much as two-thirds. It lowers the cost of installing the system, the size of the electrical service and transformers needed in the building, the amount of space needed to house the equipment or the structure needed to support rooftop equipment, the operating and maintenance costs, the peak electrical demand, etc. There is less to energy consumption, less greenhouse gas emissions, and the operating & maintenance costs are lower.

GeoExchange™ Systems

The earth is a huge solar energy collector. The average earth temperature beneath your feet is about the same as the average annual air temperature. In the Canadian prairies that’s about 40-45°F (5-7°C). In Texas, it’s about 65-70°F (18-21°C).

GeoExchange™ systems or geothermal heat pumps take advantage of the capability of the earth to store energy. A heat exchanger in the earth transfers heat by circulating fluid through a pipe buried in the ground. If the fluid is warmer than the earth, heat is transferred to the earth. If it’s colder, heat moves from the earth to the fluid. The fluid is circulated through heat pumps and either takes heat from the building (air conditioning) or puts heat into the building.

In a completely integrated mechanical system, heat pumps use two or more heat sources; the primary heat sink (in the heating mode) or the earth to store excess heat until it can be used.

                        Graphics of the integrated system 

Ice Rink Heating & Cooling

Ice rinks are unique buildings from an energy perspective. Even in the coldest part of the year, heat needs to be extracted from the ice to maintain the skating surface. The amount of heat that is extracted from the ice is dependant on a number of factors including the number of times the ice is flooded, the lighting, the temperature in the ice area, materials used in the construction of the ice area, the humidity, the number of spectators, the quality of the water used to flood the ice and the ice thickness.

The load on the refrigeration system is greatest when:

·         the ice is being heavily used

·         when the lights are on

·         the ice is being resurfaced after every practice or every period

·         the ice area air temperature is the highest

The load on the heating system is the greatest when:

·         the building is not being used

·         the ice is not being flooded

·         the lights are off

·         there are no spectators

Heat is needed when the refrigeration plant is not being used. The ice plant is used most heavily when little heat is needed. Past attempts to recapture and use the heat taken from the ice have had limited success because of the imbalance between the heating and refrigeration loads. However, using an earth loop to store excess heat when it can’t be used in the building makes the recovery of the “waste” heat possible.

Thermal Storage Buffers

Using a “thermal storage buffer” rink floor design, allows the system to store “cold” to make ice for the next day. The “buffer” can be chilled to several degrees colder than the ice surface without affecting the ice surface temperature. As it is chilled by the heat pumps, the heat taken from the “buffer” can be used for space heating, to heat domestic water, or it can be stored in the earth.

The “cold” stored in the “buffer” reduces the peak refrigeration load that must be supplied by the refrigeration plant. The smaller refrigeration means less equipment is needed, a smaller electrical service is needed, and in some cases, a smaller mechanical room is needed. 

The “buffer” allows the use of a smaller pump to circulate chilled fluid through the pipe in the rink floor. The pump needed for a conventional thin floor has to be large enough to circulate enough chilled fluid to take away all the heat hitting the floor (form flooding, radiant heat from lights, air temperature, etc.) during peak use. A floor with a massive “thermal storage buffer” however, can absorb a lot of heat just because it’s there. When the peak load is reduced, less refrigeration is needed and a smaller pump can be used.

Studies by ASHRAE (American Society of Heating, Refrigeration and Air Conditioning Engineers) have shown that up to 15% of the total load on the rink refrigeration system is from friction losses from the fluid circulating through the pipe. A smaller pump with lower flows creates less friction, reducing the overall load on the refrigeration system by as much as 10%.

The “buffer” provides several additional benefits. For example, in the event of a power failure, the massive “buffer” holds enough “cold” to prevent the ice from melting for several days.

The “cold” stored in the “buffer” is available to the ice the moment flood water hits it. When the ice is flooded the “buffer” immediately begins absorbing heat from the water and freezes it. When a thin conventional floor design is flooded, ice temperature sensors first have to activate the refrigeration system. After a few minutes, the fluid begins to chill enough to remove the heat.

The large mass of the floor gives the ice temperature more stability and consistency than a floor only a few inches thick. Conditions change very little during a hockey or curling game.