Water supply systems

Nesjavellir hot water main

From Nesjavellir geothermal power plant to Reykjavík - Iceland

  • Nesjavellir-jardvarmi

Verkís services was project management, design, preparation of tender documents and procurement: geotechnical design, mechanical design, structural design. Supervision of construction work.

 Sizes: 27 km and 1.600 l/s
 Project time:  1987 - 1990

Project overview:
The Nesjavellir main carries hot water from the Nesjavellir geothermal power plant to storage tanks in Reynisvatnsheiði, east of Reykjavík. The pipeline can carry up to 40% of the hot water demand for space heating and domestic hot water utilisation in Reykjavik.

The Nesjavellir hot water transmission main is a 27 km long insulated steel pipeline leading from the Nesjavellir geothermal power plant to the city of Reykjavík. The pipeline is DN 800 to DN 900 and has the capacity to transport up to 1.600 l/s of 100°C hot water. Project preparation began in 1987 and the main was commissioned in 1990.

The elevation of the Nesjavellir main varies from 125 m to 410 m above sea level. Water is pumped from the Nesjavellir geothermal power plant at 173 m above sea level to an accumulating tank at Háhryggur at 410 m. From there, gravity flow transports the water over 26 km to the storage tanks on Reynisvatnsheiði, located east of Reykjavík. The pipe is designed for maximum pressure of 3,6 MPa. The flow is controlled at Reynisvatnsheiði control station with the purpose of keeping the water level in the accumulating tank at Háhryggur constant.

More than 80% of the main, or 22,7 km, lies above ground. This section consists of steel pipes, insulated with rock wool and is contained within a protective aluminium sheet cover. The remaining part of the main is buried underground and is pre-insulated with polyurethane within a polyethylene casing pipe. When the flow is at its maximum level, it takes about 2 hours for the water to flow from Nesjavellir Power Plant to Reykjavík. Due to the effective insulation of the pipeline and the high speed of the water flowing through it, the temperature drop on route is only about 0,5°C.

When hot water runs through the pipeline, the thermal expansion over its length is more than 25 m. The main elements installed to compensate for this are expansion joints, loops and specially designed supports which allow the pipeline to move.