Lynne Kiesling
Sometimes the old ideas become new again … such is the case with chill storage or ice storage. Say you have a big high-rise building with air conditioning installed. In peak hours on hot days, your air conditioning use puts a lot of strain on the network, threatening a blackout. So if you are fortunate enough to be in a state that allows dynamic pricing and/or has an interruption/curtailment program at its ISO (I have the New York ISO in mind here), the high costs of producing peak power may lead to high prices and calls for interruption in those hours.
But what if you make ice overnight and let it melt during the day?
Because electricity is needed to make the ice, water is frozen in large silver tanks at night when power demands [and therefore prices — ed.] are low. The cool air emanating from the ice blocks is then piped throughout the building more or less like traditional air conditioning. At night the water is frozen again and the cycle repeats.
The quote is from this Yahoo article, which discusses the ice storage system that Credit Suisse has installed in the almost century-old MetLife Tower in New York City.
Ice storage at Credit Suisse lowers the facility’s peak energy use by 900 kilowatts, and reduces overall electric usage by 2.15 million kilowatt-hours annually — enough to power about 200 homes.
The article does a good job of pointing out that ice storage reduces peak use, overall use, and thus saves the customer money, making it a worthwhile investment. But notice also that this reduction means that it’s good for the environment.
Dynamic pricing is the driver here. Dynamic pricing aligns economic interests and environmental interests. Without the price signal and the price incentive, the impetus to make the investment to install such a system is nonexistent.
Note also that this technology begins to chip away at the tired old canard that “electricity can’t be stored”. Here’s a fairly cost-effective way to do it, if you’ve got a big enough building.
There is no reason that this technology can’t be scaled down to the residential level. If we got a large enough market with real time dynamic electric rates, there would be a market for a domestic ice making system. Companies like Carrier would provide it.
This is going to sound smug, but how exactly is this good for the environment?
Granted, it may be great for large businesses, but overall the use of refrigerant chemicals and so-called “efficient” central heating and air will likely remain the norm.
In any case, if its so good, it begs the question, why wasn’t this adopted before? What changed today?
Technically, that’s not storing electricity – you can’t use that melting ice to, say, power your computers or lights.
It’s more like (inexactly, from a physics point of view), “storing cooling”.
(The inability to electricity is one reason that wind power is a non-starter for significant use.
This cooling system, while interesting and in some manners efficient, only moves demand around, and doesn’t store electricity, which really is a different problem. Especially in winter, when you’re barely using any cooling at all in NYC.)
Technically, that’s not storing electricity – you can’t use that melting ice to, say, power your computers or lights.
It’s more like (inexactly, from a physics point of view), “storing cooling”.
(The inability to electricity is one reason that wind power is a non-starter for significant use.
This cooling system, while interesting and in some manners efficient, only moves demand around, and doesn’t store electricity, which really is a different problem. Especially in winter, when you’re barely using any cooling at all in NYC.)
Interesting idea. I understand the time-shifting benefits, but I’m unclear on how they can claim savings in their overall electrical usage. First off, if the system is truly more efficient, why don’t we see any peak-usage AC systems using the same technology? Making the ice at night can’t be that more efficient. Secondly, even if the system cuts 900 kilowatts off of their peak usage, it would have to run for almost 2400 hours to just get the quoted 2.15 million kilowatt-hours in *peak* energy savings. That’s running for an average of 6.5 hours a day, every day of the year – and that doesn’t even factor in the energy used in the off-peak hours to make the ice. Any experts care to comment?
Interesting idea. I understand the time-shifting benefits, but I’m unclear on how they can claim savings in their overall electrical usage. First off, if the system is truly more efficient, why don’t we see any peak-usage AC systems using the same technology? Making the ice at night can’t be that more efficient. Secondly, even if the system cuts 900 kilowatts off of their peak usage, it would have to run for almost 2400 hours to just get the quoted 2.15 million kilowatt-hours in *peak* energy savings. That’s running for an average of 6.5 hours a day, every day of the year – and that doesn’t even factor in the energy used in the off-peak hours to make the ice. Any experts care to comment?
If we are going to utilize a lot of intermittent energy sources, we will need to invest in methods of matching supply, which maybe unpredictable, with demand. On the supplier side equipment can be built that will store energy and release it on demand, e.g. really big batteries.
Storing cold in the form of ice is cheaper, but the capital cost falls on the customer, and it may not be as useful as electricity in all situations, like the middle of winter in the northern states.
In the example in the article, reducing peak hour consumption probably reaps an even more substantial reward from ConEd than the saving of 2GWhr in the form of off-peak pricing. If you could get a total savings of $400K/yr, you would have a 7.5 year payback, which is OK but not great.
It is undoubtedly cheaper to put this kind of system into a new building than to retrofit it into an 80 year old land-mark in the middle of a crowded city.
The article says nothing about the reasons for the energy consumption reductions. I’d be interested to know what they included.
At the building site, the reductions (if limited to those resulting directly from the use of ice storage) could be from only two sources: an increase in the Rankine cycle efficiency of the chillers, resulting from the fact that the outdoor air temperature difference (day/night) is greater than the refrigerant temperature difference between making chilled water and making ice; or, from the use of the most efficient chillers to make the ice at night, rather than all of the chillers during the day to make chilled water. If they have several older, less efficient chillers, keeping them offline by using ice could make a big difference.
Beyond the building site, they may have taken into account: the reduced need for the utility to operate its least efficient generators on peak; and/or, reduced distribution losses resulting from peak demand reduction. (Some older utility systems experience distribution losses of up to 16% on peak, compared with their annual loss percentage of ~7-8%. It would not be shock to learn that ConEd was one such utility.)
Jeffrey,
The ice storage system is charged by a centrifugal chiller which uses a synthetic refrigerant. The chiller stores “coolth” as ice when the system has excess capacity and then uses the stored “coolth” on-peak to reduce electric demand.
Fat Man,
Similar tanks can store heat as well, if winter peaking is an issue.
The article says nothing about the reasons for the energy consumption reductions. I’d be interested to know what they included.
At the building site, the reductions (if limited to those resulting directly from the use of ice storage) could be from only two sources: an increase in the Rankine cycle efficiency of the chillers, resulting from the fact that the outdoor air temperature difference (day/night) is greater than the refrigerant temperature difference between making chilled water and making ice; or, from the use of the most efficient chillers to make the ice at night, rather than all of the chillers during the day to make chilled water. If they have several older, less efficient chillers, keeping them offline by using ice could make a big difference.
Beyond the building site, they may have taken into account: the reduced need for the utility to operate its least efficient generators on peak; and/or, reduced distribution losses resulting from peak demand reduction. (Some older utility systems experience distribution losses of up to 16% on peak, compared with their annual loss percentage of ~7-8%. It would not be shock to learn that ConEd was one such utility.)
Jeffrey,
The ice storage system is charged by a centrifugal chiller which uses a synthetic refrigerant. The chiller stores “coolth” as ice when the system has excess capacity and then uses the stored “coolth” on-peak to reduce electric demand.
Fat Man,
Similar tanks can store heat as well, if winter peaking is an issue.
The article says nothing about the reasons for the energy consumption reductions. I’d be interested to know what they included.
At the building site, the reductions (if limited to those resulting directly from the use of ice storage) could be from only two sources: an increase in the Rankine cycle efficiency of the chillers, resulting from the fact that the outdoor air temperature difference (day/night) is greater than the refrigerant temperature difference between making chilled water and making ice; or, from the use of the most efficient chillers to make the ice at night, rather than all of the chillers during the day to make chilled water. If they have several older, less efficient chillers, keeping them offline by using ice could make a big difference.
Beyond the building site, they may have taken into account: the reduced need for the utility to operate its least efficient generators on peak; and/or, reduced distribution losses resulting from peak demand reduction. (Some older utility systems experience distribution losses of up to 16% on peak, compared with their annual loss percentage of ~7-8%. It would not be shock to learn that ConEd was one such utility.)
Jeffrey,
The ice storage system is charged by a centrifugal chiller which uses a synthetic refrigerant. The chiller stores “coolth” as ice when the system has excess capacity and then uses the stored “coolth” on-peak to reduce electric demand.
Fat Man,
Similar tanks can store heat as well, if winter peaking is an issue.
The peak demand savings sound real and the value could be significant – just look at the on peak to off peak real time prices for hot summer days at nyiso.com. However, the overall energy savings (and thus overall environmental benefits such as greenhouse gases,etc)seem way overstated. Even if the chillers operate more efficiently at night with lower temperature differentials, there has to be some conversion losses associated. I find it hard to believe there would be any substantial energy savings.
When a centrifugal chiller is operating to make ice (25 – 28 deg. F). It is operating with a much lower suction pressure. This mode of operation is less efficient for the chiller thant operating at the normal chilled water temperature of 45 deg. F. Therfore I fail to see that the overall consumption of fuel to produce electrical energy is reduced. The ecconomic benefits of an ice storage system are obvious, due to on peak pricing, however overall use of natural resources would appear to be greater with this system than continuous chilled water cooling
When a centrifugal chiller is operating to make ice (25 – 28 deg. F). It is operating with a much lower suction pressure. This mode of operation is less efficient for the chiller thant operating at the normal chilled water temperature of 45 deg. F. Therfore I fail to see that the overall consumption of fuel to produce electrical energy is reduced. The ecconomic benefits of an ice storage system are obvious, due to on peak pricing, however overall use of natural resources would appear to be greater with this system than continuous chilled water cooling
The following is quoted from an ASHRAE Journal article 9/2003; TES Myths
When analyzing energy savings with ice storage you must consider both energy used at the building and energy used at the source of
generation at the power plant. The reason is simple. Most energy-efficient products reduce energy use but do not change when energy is used. As an industry, we have done a poor job of relaying the energy saving benefits of OPC beyond the meter. Site energy savings may or may not occur. Source energy savings almost always occur.
Site Energy Savings Is the goal to save the most energy or energy costs? Clearly the owner’s answer is the latter. However, energy-efficiency
funding from most states is based on kWh saved. With thermal storage, optimizing for energy savings can be done but often is not the same as maximizing energy cost reduction. So let’s
review a design maximizing energy savings for air-cooled and water-cooled applications. First, an air-cooled chiller operating at ARI design conditions,95°F/45°F (35°C/7°C)uses the same
kW/ton at ice-making conditions of 78°F/25°F (26°C/–4°C)Therefore, a 17°F (9°C) change in dry bulb
gives equal efficiency for ice making. In much of the country,the ambient day to night swing is 20°F (11°C). Because the swing is sinusoidal, the average for the on-peak hours versus the ice-making hours make the average temperature swing more like 12°F to 14°F (7°C to 8°C). If you then factor in:
1. Undersized chillers are fully loaded for a majority of the hours of operation, normally their most efficient condition.
2. Chillers in a partial storage system normally operate upstream of ice storage. Therefore, the chillers cool the upper half of the delta T, and have higher on-peak efficiencies than if they were producing 45°F (7°C) liquid (Point C in Figure 3).
3. Extreme part-load conditions can be met fully with ice to avoid short cycling of chiller equipment (0% to 20%), which is clearly very inefficient. For water-cooled OPC applications, the argument is less clear initially for site energy savings. Ambient wet-bulb temperature
only decreases about 5°F to 7°F (3°C to 4°C) from
day to night. Therefore, this decrease does not make up for the lower evaporator temperatures required for ice making, yielding about a 15% “penalty” (Figure 4) (Point A to B).
However, the most important point is the amount of ton-hrs per year that are actually met with ice in a design focused on energy savings. In a standard chiller priority, partial storage
system, where a 50% sized chiller(s) would work, but a 60% sized chiller is installed, a simple bin analysis shows that the amount of ton-hrs per year in an office building or school above 60% is only about 20%. So with the ice-making penalty
for air-cooled chillers arguably at 0%, and 15% for water-cooled, the total ice-making penalty for water-cooled is 20% of 15% or about 3%. Even with the extra pumping required to put cooling into storage, when the points made earlier for air-cooled are factored in, it is arguable that the water-cooled difference drops to nil.
Routine oversizing of chillers causes related components to be oversized including condenser pumps, and cooling towers and transformers, which likely will never run at full load for the life of the system. Right-sizing chiller capacity is
capable of saving lots of energy, as discussed by Tom Hicks. The best way to conceptualize the energy advantages of “right-sizing” a system with storage is to compare it to the value gained by using variable frequency drives (VFD) on motors. VFDs vary the speed to match part-load conditions:
storage allows varying the time at full load, of a smaller cooling plant (which is like having VFDs on the chiller, condenser pump and cooling tower fan). Major advantages can be captured here that are yet to be quantified by accurate
simulations.
Source Energy Savings
The California Energy Commission released a report9 in 1996 that clearly concluded that, for two of the major California utilities,it is 8% to 30% more efficient to create and deliver a kWh
during off-peak hours than during on-peak hours. The combination of using more efficient base load generation plants, lower transmission and distribution line losses and cooler nighttime
temperatures combine to create more efficient nighttime generation. Therefore, if we assume that a building uses the same amount of kWh before and after an OPC system is installed,
major “source energy” savings exist for each kWh shifted to offpeak. In addition, there are environmental benefits. In regards to
an ice storage installation(s) in Manhattan, Ashok Gupta of the Natural Resources Defense Council stated, “Peak shaving results in lower
emissions, because some of the plants used to meet demand peaks are among the dirtiest in the city.”10 In response to these findings, California’s 2005 release of the Title 24 energy codewill value the relative cost of energy for every hour of the year (instead of a flat rate as allowed in 90.1), otherwise known as “time dependent valuation.” With relative costs of three to four times as high on summer afternoons, the code will surely drive designers to use more efficient, off-peak power and ice storage.
The following is quoted from an ASHRAE Journal article 9/2003; TES Myths
When analyzing energy savings with ice storage you must consider both energy used at the building and energy used at the source of
generation at the power plant. The reason is simple. Most energy-efficient products reduce energy use but do not change when energy is used. As an industry, we have done a poor job of relaying the energy saving benefits of OPC beyond the meter. Site energy savings may or may not occur. Source energy savings almost always occur.
Site Energy Savings Is the goal to save the most energy or energy costs? Clearly the owner’s answer is the latter. However, energy-efficiency
funding from most states is based on kWh saved. With thermal storage, optimizing for energy savings can be done but often is not the same as maximizing energy cost reduction. So let’s
review a design maximizing energy savings for air-cooled and water-cooled applications. First, an air-cooled chiller operating at ARI design conditions,95°F/45°F (35°C/7°C)uses the same
kW/ton at ice-making conditions of 78°F/25°F (26°C/–4°C)Therefore, a 17°F (9°C) change in dry bulb
gives equal efficiency for ice making. In much of the country,the ambient day to night swing is 20°F (11°C). Because the swing is sinusoidal, the average for the on-peak hours versus the ice-making hours make the average temperature swing more like 12°F to 14°F (7°C to 8°C). If you then factor in:
1. Undersized chillers are fully loaded for a majority of the hours of operation, normally their most efficient condition.
2. Chillers in a partial storage system normally operate upstream of ice storage. Therefore, the chillers cool the upper half of the delta T, and have higher on-peak efficiencies than if they were producing 45°F (7°C) liquid (Point C in Figure 3).
3. Extreme part-load conditions can be met fully with ice to avoid short cycling of chiller equipment (0% to 20%), which is clearly very inefficient. For water-cooled OPC applications, the argument is less clear initially for site energy savings. Ambient wet-bulb temperature
only decreases about 5°F to 7°F (3°C to 4°C) from
day to night. Therefore, this decrease does not make up for the lower evaporator temperatures required for ice making, yielding about a 15% “penalty” (Figure 4) (Point A to B).
However, the most important point is the amount of ton-hrs per year that are actually met with ice in a design focused on energy savings. In a standard chiller priority, partial storage
system, where a 50% sized chiller(s) would work, but a 60% sized chiller is installed, a simple bin analysis shows that the amount of ton-hrs per year in an office building or school above 60% is only about 20%. So with the ice-making penalty
for air-cooled chillers arguably at 0%, and 15% for water-cooled, the total ice-making penalty for water-cooled is 20% of 15% or about 3%. Even with the extra pumping required to put cooling into storage, when the points made earlier for air-cooled are factored in, it is arguable that the water-cooled difference drops to nil.
Routine oversizing of chillers causes related components to be oversized including condenser pumps, and cooling towers and transformers, which likely will never run at full load for the life of the system. Right-sizing chiller capacity is
capable of saving lots of energy, as discussed by Tom Hicks. The best way to conceptualize the energy advantages of “right-sizing” a system with storage is to compare it to the value gained by using variable frequency drives (VFD) on motors. VFDs vary the speed to match part-load conditions:
storage allows varying the time at full load, of a smaller cooling plant (which is like having VFDs on the chiller, condenser pump and cooling tower fan). Major advantages can be captured here that are yet to be quantified by accurate
simulations.
Source Energy Savings
The California Energy Commission released a report9 in 1996 that clearly concluded that, for two of the major California utilities,it is 8% to 30% more efficient to create and deliver a kWh
during off-peak hours than during on-peak hours. The combination of using more efficient base load generation plants, lower transmission and distribution line losses and cooler nighttime
temperatures combine to create more efficient nighttime generation. Therefore, if we assume that a building uses the same amount of kWh before and after an OPC system is installed,
major “source energy” savings exist for each kWh shifted to offpeak. In addition, there are environmental benefits. In regards to
an ice storage installation(s) in Manhattan, Ashok Gupta of the Natural Resources Defense Council stated, “Peak shaving results in lower
emissions, because some of the plants used to meet demand peaks are among the dirtiest in the city.”10 In response to these findings, California’s 2005 release of the Title 24 energy codewill value the relative cost of energy for every hour of the year (instead of a flat rate as allowed in 90.1), otherwise known as “time dependent valuation.” With relative costs of three to four times as high on summer afternoons, the code will surely drive designers to use more efficient, off-peak power and ice storage.
The following is quoted from an ASHRAE Journal article 9/2003; TES Myths
When analyzing energy savings with ice storage you must consider both energy used at the building and energy used at the source of
generation at the power plant. The reason is simple. Most energy-efficient products reduce energy use but do not change when energy is used. As an industry, we have done a poor job of relaying the energy saving benefits of OPC beyond the meter. Site energy savings may or may not occur. Source energy savings almost always occur.
Site Energy Savings Is the goal to save the most energy or energy costs? Clearly the owner’s answer is the latter. However, energy-efficiency
funding from most states is based on kWh saved. With thermal storage, optimizing for energy savings can be done but often is not the same as maximizing energy cost reduction. So let’s
review a design maximizing energy savings for air-cooled and water-cooled applications. First, an air-cooled chiller operating at ARI design conditions,95°F/45°F (35°C/7°C)uses the same
kW/ton at ice-making conditions of 78°F/25°F (26°C/–4°C)Therefore, a 17°F (9°C) change in dry bulb
gives equal efficiency for ice making. In much of the country,the ambient day to night swing is 20°F (11°C). Because the swing is sinusoidal, the average for the on-peak hours versus the ice-making hours make the average temperature swing more like 12°F to 14°F (7°C to 8°C). If you then factor in:
1. Undersized chillers are fully loaded for a majority of the hours of operation, normally their most efficient condition.
2. Chillers in a partial storage system normally operate upstream of ice storage. Therefore, the chillers cool the upper half of the delta T, and have higher on-peak efficiencies than if they were producing 45°F (7°C) liquid (Point C in Figure 3).
3. Extreme part-load conditions can be met fully with ice to avoid short cycling of chiller equipment (0% to 20%), which is clearly very inefficient. For water-cooled OPC applications, the argument is less clear initially for site energy savings. Ambient wet-bulb temperature
only decreases about 5°F to 7°F (3°C to 4°C) from
day to night. Therefore, this decrease does not make up for the lower evaporator temperatures required for ice making, yielding about a 15% “penalty” (Figure 4) (Point A to B).
However, the most important point is the amount of ton-hrs per year that are actually met with ice in a design focused on energy savings. In a standard chiller priority, partial storage
system, where a 50% sized chiller(s) would work, but a 60% sized chiller is installed, a simple bin analysis shows that the amount of ton-hrs per year in an office building or school above 60% is only about 20%. So with the ice-making penalty
for air-cooled chillers arguably at 0%, and 15% for water-cooled, the total ice-making penalty for water-cooled is 20% of 15% or about 3%. Even with the extra pumping required to put cooling into storage, when the points made earlier for air-cooled are factored in, it is arguable that the water-cooled difference drops to nil.
Routine oversizing of chillers causes related components to be oversized including condenser pumps, and cooling towers and transformers, which likely will never run at full load for the life of the system. Right-sizing chiller capacity is
capable of saving lots of energy, as discussed by Tom Hicks. The best way to conceptualize the energy advantages of “right-sizing” a system with storage is to compare it to the value gained by using variable frequency drives (VFD) on motors. VFDs vary the speed to match part-load conditions:
storage allows varying the time at full load, of a smaller cooling plant (which is like having VFDs on the chiller, condenser pump and cooling tower fan). Major advantages can be captured here that are yet to be quantified by accurate
simulations.
Source Energy Savings
The California Energy Commission released a report9 in 1996 that clearly concluded that, for two of the major California utilities,it is 8% to 30% more efficient to create and deliver a kWh
during off-peak hours than during on-peak hours. The combination of using more efficient base load generation plants, lower transmission and distribution line losses and cooler nighttime
temperatures combine to create more efficient nighttime generation. Therefore, if we assume that a building uses the same amount of kWh before and after an OPC system is installed,
major “source energy” savings exist for each kWh shifted to offpeak. In addition, there are environmental benefits. In regards to
an ice storage installation(s) in Manhattan, Ashok Gupta of the Natural Resources Defense Council stated, “Peak shaving results in lower
emissions, because some of the plants used to meet demand peaks are among the dirtiest in the city.”10 In response to these findings, California’s 2005 release of the Title 24 energy codewill value the relative cost of energy for every hour of the year (instead of a flat rate as allowed in 90.1), otherwise known as “time dependent valuation.” With relative costs of three to four times as high on summer afternoons, the code will surely drive designers to use more efficient, off-peak power and ice storage.
I like ideas like this, but I have a worry.
It seems to me that there is a poorly measured opportunity cost here with low probability of extremely costly water-bred airborne infection.
The cooling system discussed here and fitted with ice storage is a chilled water system. The water side is a closed system and has been used for large buildings for years and years. BTU’s are transfered from the room air to the surface of the coil fins which are connected to the closed pipe. Pumping water around a building is much safer and more cost effective than pumping refrigerant through the pipes. Water bred aireborn infections come from cooling towers and airhandlers with non emptying drain pans, not chilled water pipes.
Cooling costs are typically 60% of a buildings summertime electricity costs and if by applying ice storage systems one can cut 20%-40% of the cooling costs or 10%-20% of the entire buildings electricity costs, then give me more poorly measured opportunities. Oh, and summer demand is lowered, emissions are lowered, and less source fuel is used and new power plant projects are delayed. Seems like a more practical solution to growth is to balance current assets, treat efficiency like a resource and balance these opportunities with renewables. No one idea is the magic answer here.
The cooling system discussed here and fitted with ice storage is a chilled water system. The water side is a closed system and has been used for large buildings for years and years. BTU’s are transfered from the room air to the surface of the coil fins which are connected to the closed pipe. Pumping water around a building is much safer and more cost effective than pumping refrigerant through the pipes. Water bred aireborn infections come from cooling towers and airhandlers with non emptying drain pans, not chilled water pipes.
Cooling costs are typically 60% of a buildings summertime electricity costs and if by applying ice storage systems one can cut 20%-40% of the cooling costs or 10%-20% of the entire buildings electricity costs, then give me more poorly measured opportunities. Oh, and summer demand is lowered, emissions are lowered, and less source fuel is used and new power plant projects are delayed. Seems like a more practical solution to growth is to balance current assets, treat efficiency like a resource and balance these opportunities with renewables. No one idea is the magic answer here.
The cooling system discussed here and fitted with ice storage is a chilled water system. The water side is a closed system and has been used for large buildings for years and years. BTU’s are transfered from the room air to the surface of the coil fins which are connected to the closed pipe. Pumping water around a building is much safer and more cost effective than pumping refrigerant through the pipes. Water bred aireborn infections come from cooling towers and airhandlers with non emptying drain pans, not chilled water pipes.
Cooling costs are typically 60% of a buildings summertime electricity costs and if by applying ice storage systems one can cut 20%-40% of the cooling costs or 10%-20% of the entire buildings electricity costs, then give me more poorly measured opportunities. Oh, and summer demand is lowered, emissions are lowered, and less source fuel is used and new power plant projects are delayed. Seems like a more practical solution to growth is to balance current assets, treat efficiency like a resource and balance these opportunities with renewables. No one idea is the magic answer here.