Highly Renewable District Heat for Espoo Utilizing Waste Heat Sources

Overview

The district heating operator Fortum and the city of Espoo have set a goal to abandon coal and raise the renewable share to 95% by 2029, and Fortum is considering using waste heat from a large data centre. The study investigates feasibility and the required amount of waste heat. Two operation strategies are introduced, one based on marginal costs and one prioritising waste heat utilisation, each modelled with three electricity price scenarios. Because low-temperature waste heat from a data centre must be primed by heat pumps, electricity price significantly affects feasibility.

The Espoo DH network serves over 80% of the population in Espoo and neighbouring cities, with total annual heat demand of about 2.6 TWh. Waste-heat sources already connected include Espoo hospital (1.5 MW) and an Ericsson data centre (2.8 MW), and a 100 MW data centre was planned. Heat-recovery heat-pump COP depends on the data-centre cooling system: all-liquid cooling recovers heat at 50-60 °C with COP up to 6.3, mixed air-liquid reaches COP 5.5 and air-cooled systems reach 4.1.

In the highest electricity price scenario, 200 MW of data-centre heat-pump capacity is needed to reach 95% renewables under marginal-cost dispatch, versus 150 MW if waste heat is prioritised. The investment analysis assumed a 20-year heat-pump lifetime; the investment is feasible in the two lower electricity price scenarios, but NPV is negative over that lifetime at the highest price. Data-centre waste heat suits base load and fits poorly as a replacement for peak heat-only boilers, and the capacity needed for 95% renewables already exceeds summer minimum demand.

Prioritising waste heat leads to higher production costs but needs less capacity, and high electricity prices undermine heat-pump economics. Liquid cooling and low-temperature DH would improve utilisation of waste heat. Limits: the modelling is for a single city and operating system, so results depend on the Espoo network and Fortum assets.

Key points

1. The Espoo DH network serves over 80% of the population in Espoo and neighbouring cities, with total annual heat demand of about 2.6 TWh.
2. Waste-heat sources already connected include Espoo hospital (1.5 MW) and an Ericsson data centre (2.8 MW); a 100 MW data centre was planned in Espoo.
3. Heat-recovery heat-pump COP depends on the cooling system: all-liquid cooling recovers heat at 50-60 °C with COP up to 6.3, mixed air-liquid COP 5.5, air-cooled 4.1.
4. In the highest electricity price scenario, 200 MW of data-centre heat-pump capacity is needed to reach 95% renewables under marginal-cost dispatch, versus 150 MW if waste heat is prioritised.
5. The investment analysis assumed a 20-year heat-pump lifetime; it is feasible in the two lower electricity price scenarios, but NPV is negative at the highest price.
6. Data-centre waste heat suits base load and fits poorly as a replacement for peak heat-only boilers; the capacity needed for 95% renewables already exceeds summer minimum demand.

Using it in design

• In selling data-centre waste heat, set heat-pump COP by cooling type (all-liquid 6.3, mixed 5.5, air-cooled 4.1) and include electricity price sensitivity in the feasibility study.
• Check waste-heat capacity against summer minimum demand; if the required capacity exceeds it, use is limited and it cannot replace peak boilers.
• Evaluate liquid cooling (recovery at 50-60 °C) and low-temperature district heating as design options that improve waste-heat use.

Who should read it

Operators, planners and data-centre designers planning to integrate data-centre waste heat into district heating systems.

Document contents

1. 1. Introduction
2. 2. Materials and Methods (2.1 External factors, 2.2 Heat Pumps, 2.3 Buy-In Heat, 2.4 Assumptions, 2.5 Investment Analysis)
3. 3. Results (marginal-cost strategy, 3.2 Operation Strategy Prioritizing Waste Heat, 3.3 Fuel Consumption, 3.4 Investment Analysis)
4. 4. Discussion (4.1 The Goal of 95% of Renewable Production Can Be Achieved, 4.3 Waste Heat Cannot Replace Winter Peak Production in Espoo, 4.5 Liquid Cooling and LTDH Would Improve Utilization of Waste Heat, 4.6 Employment Shifts to IT Sector)
5. 5. Conclusions

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Publication details

Authors

Pauli Hiltunen; Sanna Syri

Publisher

Energies (MDPI AG)

Year

2020

Volume

13

Issue

14

Pages

3551

Document language

English

Source type

Scientific

Access

Open licence — downloadable

DOI

10.3390/en13143551

Licence

CC BY 4.0 — share with attribution

Licence evidence

www.mdpi.com

Citation