What You Need to Know When Calculating Load Profiles for an Optimal Combined Heat and Power (CHP) System

Posted by Ian Hopkins on 21-Feb-2017 11:00:00

In order to generate a load profile for an optimal CHP system, you need to know what the existing heat and power consumption against time of the building is and how you can measure it.

What you need to know when building load profiles for an optimal CHP system-01.pngUnderstanding precisely how a site’s buildings and processes consume energy is crucial to deciding whether there is scope for a Combined Heat and Power (CHP) unit to be installed.

What is a load profile?

Energy load profiles are a representation of the site’s existing energy consumption, or load. When the site’s electrical and thermal energy loads are plotted graphically against time, they visually portray a pattern of how much energy is required on site at a specific time.

Why are load profiles important for CHP sizing?

For CHP to be economically viable, its operation must be optimised. If the full benefits of energy cost savings and a reduction in carbon emissions are to be achieved, a CHP system needs to be sized correctly to operate at its optimal performance output. It therefore needs to match the site’s actual energy load profiles as closely as possible.

Data collection

In order to calculate load profiles, data needs to be collected to show how and when energy is actually required. The more information gathered, the better the calculations and the load profiles produced.

Data can be gathered by:

  • Monitoring information from a site’s building energy management system (BEMS) – this might even generate the various profiles required.

  • Analysing the current year’s bills for electricity and the fuel used to generate on-site space heating and hot water. These are generally monthly or quarterly. Ideally previous years’ bills will also provide invaluable information to explain any annual variances.

  • Contacting your energy suppliers to request hourly, or even better, half hourly meter readings. This will ultimately provide a better understanding of patterns of energy use and better load profiles.

  • If hourly readings are unavailable, short-term monitoring may be used to measure actual energy consumption.

Energy audits, like those now carried out under the Energy Savings Opportunity Scheme (ESOS) and/or by special third party assessors, will provide a basis for acquiring good, reliable information.

Checking data reliability

If in recent years there have been noticeable variations in seasonal temperatures, it will be beneficial to also check the information from previous years, make any adjustments and check if this provides a more representative profile. The more detailed the analysis carried out at this stage, the more the CHP system’s performance can be optimised in design.

It is also essential to establish if the data is and will continue to be representative of the site’s actual energy loads going forward. The following needs to be checked and confirmed:

  • Are there any proposed changes to the site’s energy requirements in the future that could increase or decrease the energy load, i.e. have energy saving measures been implemented, such as energy-efficient lighting and/or insulation, or are likely to be?

  • Don't forget the flip side. The site might be about to be redeveloped or expanded in which case a bigger CHP unit might be beneficial.

  • Can operational savings be made by making processes and equipment operate more efficiently, i.e. upgrading/replacement of inefficient boilers?

  • Have cooling loads been accounted for? (Electric cooling could be replaced with equipment that uses heat energy to generate chilled water, e.g. absorption chillers.)

  • Could the system be operated at a slightly lower return temperature, which might provide a better option for a constant heat load/demand?

Compiling the data

The data gathered should be compiled and plotted graphically against time to show how energy consumption varies:

  • At different times of day (morning/afternoon/evening peaks and troughs).

  • On different days of the week (is energy load constant at the weekend).

  • With seasonal variations (summer loads versus winter loads – heating may be greater in winter, but is cooling required in the summer?).

Plotting the actual energy load against annual total hours will also produce a load duration curve, which is hugely useful for visualising how a CHP system (operating as lead boiler) can operate with support from a secondary boiler (for peak loads), or with multiple CHP units to  accommodate a widely varying load.

Takeaways:

  • In order to generate a load profile, you need to know what the existing heat and power consumption pattern is.

  • If there is an energy management system in place, it will be fairly simple to gather the recorded metering data to understand the energy profile.

  • If there is no energy management system in place, the consumption needs to be calculated from information recorded on monthly bills.

  • Other options include the installation of a meter on a short-term basis, followed by interviews with the site owner and/or personnel.

  • The more granular the data the better the model and hence the more optimal the CHP sizing will be. 

Build more accurate cogeneration load profiles with our technical guide. Download How building consultants can complete an end-to-end Combined Heat and Power (CHP) economic feasibility study now.CHP-FAQ,-feasibility-and-load-profiling.jpg

Topics: CHP / Cogeneration

Ian Hopkins

Ian Hopkins is a technical sales professional and business leader with more than 15 years’ experience in delivering energy efficiency projects and strategy in Europe and the United States. Ian currently heads up the Sales and Marketing function as one of the board directors at ENER-G Combined Power Ltd.