Case Study: Air Cooled Ice Machines
Conducted by: PG&E Food Service Technology Center
How a restaurant saved $303 annually in energy and water costs by switching to a higher efficiency ice machine model.
Background
There are two parts to this case study.
The first part takes a look at 8 separate ice machines in 8 different restaurants (one machine from each restaurant). These are older models that are already installed in their respective restaurants. For each machine, the projected energy savings are calculated. Additionally, Ice Machine #2 was used as the basis to determine the potential of switching to a load-shifting strategy.
The idea of the load-shifting method is for the machine to stop working during a restaurant’s peak periods. This saves energy since energy is only used when making the ice (the insulated ice storage bins don’t need energy).
Hypothetically, if the ice within the storage bin is enough to meet the restaurant’s needs (aka. no impact on their operations) throughout the day, then the load-shifting method is the most efficient. Additionally, if a restaurant needs more ice during the peak periods, an "automated demand response” can be added to detect when more ice is needed.
In the second part, one of the 8 ice machines from the first study was selected and fitted with energy and water meters. Its data was collected for 3 weeks. Then, the older model ice machine was replaced with an ENERGY STAR® ice machine, and data was collected for another 3 weeks. Afterwards, this machine was switched to a load-shifting strategy for another week to test the feasibility of the strategy on the newer model.
Results
Study #1
Water + electrical usage data were collected from an ice machine in each of the 8 restaurants.
3 of the 8 machines showcased potential savings close to 2300 kWh per year
1 machine had the potential to save ~6000 kWh per year
3 machines had peak duty cycles below 70% (they rarely ran out of ice during peak periods)
3 machines had average duty cycles below 70% but had peak duty cycles greater than 90% (they sometimes ran out of ice during peak periods)
For these machines, a load-shifting strategy + a demand response program would be the best solution
2 machines were undersized and therefore had average duty cycles greater than 80% and peak duty cycles greater than 100% (on days of heavy demand for ice, the machines must run all day)
Ice machine #2 was used as the basis to determine the potential of the load-shifting strategy
Ice machine #2:
Located in a full-service restaurant that is open for lunch and dinner 7 days a week
Utilized one bin with 2 stacked air-cooled ice-making heads
Average electrical consumption ~55.4 kWh/day
Coincident peak demand of 4.83 kW
Projected annual electricity cost = $3172
Average duty cycle of 50% (maximum = 65%)
When utilizing the load-shifting strategy:
Energy cost savings: $355
Demand charge savings: $839
Total annual cost savings: $1194
38% reduction in total electricity cost
From $3172 to $1978
Study #2
An older model ice machine (with a 380lbs production capacity + 310lbs bin capacity) was replaced with a new ENERGY STAR® machine
The new machine had a 410 lbs production capacity and a 430 lbs bin capacity
The new machine was able to switch to a load-shifting strategy
It was programmed for ice production only between 6pm - 12am
Results:
Existing machine (old machine):
Energy consumption rate: 6.54 kWh per 100 lbs of ice
Average cycle power: 1.05 kW
Duty cycle: 64%
Water use rate: 28.0 gal per 100 lbs of ice
Calculated field ice production capacity over a 24-hour period: 390 lbs
Replacement ice machine (ENERGY STAR® machine):
Energy consumption rate: 4.34 kWh per 100lb of ice
34%, 2.2kWh per 100 lbs reduction in energy
Average cycle power: 0.89 kW
15%, 0.16 kW reduction in power
Duty cycle: 37%
42% run time reduction
Water use rate: 24.0 gal per 100 lbs of ice
14%, 4.0 gal per 100 lbs reduction
Calculated ice production capacity: 497 lbs per 24-hours
Overall, replacing the old machine with a newer, more efficient model led to this restaurant saving $303 in annual energy and water costs.
Shifting to the load shifting strategy:
For this establishment, the load shifting strategy was a success. There was no need for afternoon/peak period ice production; there was enough ice in the bin.
This strategy allowed for less cycles throughout the day thereby saving power