Energy quality relates to energy supply temperatures. Instead of the exergy term, a TEA curve was introduced for evaluating the planned 100 GWh district heating system of Fornebu, outside Oslo.

The questions that were raised when analyzing the energy system were:

-- how could we make a design that improves the use of low temperature energy?

-- is a design with low flow rate, i.e. low pipeline costs, compatible with the use of low temperature energy?

-- can we visualize the quality of the energy used through the distributed temperatures and the corresponding quantity of energy?

The TEA curve has the energy supply temperature on the x-axis and the energy supply quantity on the y-axis. Exemplified the TEA curve is calculated as follows, and adds it up over one year: When the water supply/return temperature is 75°C/40°C then 0% of the power is supplied at temperatures below 40°C, 34% below 52°C, and 100% below 75°C. On this basis an annual duration curve, TEA curve, covering the different supply/return water temperatures over a year, can be made.

A spreadsheet analysis tool for the TEA curve was implemented, and used for the heating plant design and optimiza-tion at Fornebu.

The paper presents the TEA curve and shows how evaluations may be done. Different design temperatures ranging from 60°C/50°C to 110°C/40°C are included in the discussion.

The main findings are:

-- The TEA curve demonstrates clearly the use of energy quality

-- Avoid shunting; -utilize the available high temperatures when possible

--A 75°C/40°C design improves the level of energy use compared to a 60°C/50°C design.

Units: I-P