Con Edison has implemented winter demand billing for Service Classification (SC) 2 and 3 customers whose annual consumption exceeds 22,000 Mlbs. To help those customers minimize the impact of demand billing, the following measures may be considered for implementation. These measures may reduce steam demand during the on–peak time interval of 6:00 am to 11:00 am on winter weekdays. However, overall steam consumption might not be reduced. For tips on conserving steam click here. Please call the Steam Business Development Group at 1-212-460-2011 with any additional steam demand reduction measures that we should include in this list.
1. Storage of Thermal Energy in Existing Mechanical systems (STEEMs)
STEEMs is a steam demand reduction strategy developed by Con Edison Steam Operations for the benefit of our demand-billed steam customers. Under STEEMs operation, the building management system (BMS) is programmed to reduce the building’s on-peak steam demand by using stored thermal energy in the building’s existing mechanical systems. Con Edison experimented with STEEMs at two customer locations. Comfort conditions were not affected at either location when operating in the STEEMs mode.
A building is a good candidate for implementing STEEMs, if it meets all of the following criteria:
- It uses circulating hot water for space heating
- Each of its terminal heating units (e.g. induction units, fan coil units and fan powered boxes) has a local thermostatically controlled valve to avoid space overheating
- It has a programmable building management system
Two STEEMs techniques have been developed:
- STEEMs using Dynamic Response
- STEEMs using Scheduled Reset
Please contact the Steam Business Development Group at 1-212-460-2011 for more information on these techniques.
2. Preheat the Building
Many buildings experience an increased level of steam demand at the time they begin operating their heating systems on cold winter mornings. This increased load may last for up to two hours before subsiding. If the building heating systems are started at 4:00 am, steam demand may be substantially reduced by 6:00 am.
Careful consideration should be given to starting up the fans earlier than normal. The increase in electric costs due to longer fan operation may exceed the savings derived from reduced steam demand. One way of minimizing this risk is to start up at an earlier time only those fans that serve the coldest spaces in the building. When these fans are started, the supply air temperature set point should be as high as practically possible to heat up the spaces as quickly as possible prior to 6:00 am. If these spaces are unoccupied, keep the fresh air dampers closed during start up.
3. Stagger Fan Start Ups in the Morning
One reason for the increase in steam demand during morning heating system startup in commercial buildings is that air handling units use steam to bring the spaces up to the daytime set point temperature. If startup of air handling units is staggered over a three hour period instead of starting all the units simultaneously, the morning peak may be reduced.
4. Do Not Raise Circulating Water Temperatures During the On-Peak Period
The circulating water heat exchangers have a significant impact on peak steam demand. If the water temperature is raised during the on-peak period, the steam demand may increase significantly until the water temperature set point is satisfied. If you need to raise the water temperatures during the on-peak period without substantially increasing your on-peak demand, you may be able to do so by incorporating a simple program into the BMS. The BMS should, in this case, be programmed to reset the water temperature set point at a constant rate over a two hour period, from an existing water temperature to a desired water temperature. Otherwise, you may consider raising water temperatures either before 6:00 am or after 11: 00 am.
5. Reduce Space Air Temperature Set Points During the On-Peak Period
Consider reducing space air temperature set point by several degrees at morning start up and keeping them down until 11:00 am, the end of the on peak period. This may reduce steam demand and consumption.
For more information on any of these Tips see our Best Practices Report:
The Steam Use Efficiency and Demand Reduction Best Practices Report
This comprehensive report provides you with recommendations to help reduce your building’s peak steam demand and overall steam consumption