Seawater heat on the Baltic coast

1Background

Surface water is an open source: extracted heat is constantly replenished – unlike the same hotel’s BHE field, which needed approx. 95 % recharge [6]. In Neustadt in Holstein, an approx. 700 kW seawater heat pump has fed a heat network since 2026 [3], [4].

2Source capacity and flow rate

Heating capacity and COP give the extraction capacity, hence the flow rate:

Q̇_H heating capacity · Q̇_Q extraction capacity · ρ·c_p ≈ 4.1–4.2 MJ/(m³·K) · ΔT seawater cooling

Halving the permissible cooling doubles the pumping rate; filters and pipe cross-section grow with it, pump power even more.

3Winter governs the design

In February the water averages 2 °C, at minimum 0 °C. The outlet temperature governs: brackish water freezes at approx. −0.5 to −1 °C. With 2 to 3 K cooling, the outlet would at times reach 0 to −2 °C from December to March (Figure 1a); extraction must then be throttled or topped up by peak load. Half the cooling and 2.3 times the load give – with a slightly smaller source share – approx. four times the August flow rate in February; peak capacity occurs in December and January. The LAWA recommendations (above 3 °C, max. 5 K, 1 K/h) apply only to rivers and lakes [2]; for the Baltic Sea, the water authority decides.

4Study results

Of the sources studied, only seawater carries the base load (Table 1), with peak load on cold days. With its higher SPF it supplies more source energy than the BHE field in [6] (1 410 MWh/a); the field could be charged with seawater in summer.

5Permitting and engineering

The return flow is a discharge under § 9(1) No. 4 WHG requiring a permit (§ 8); the water authority also assesses the abstraction from coastal waters [1]. Depending on location, the waterways office (§ 31 WaStrG), coastal protection and Natura 2000 are also involved. Schleswig-Holstein has a 150 m protection strip, with exceptions e.g. for installations permitted under water law [5].

• Design for winter: outlet well above freezing, throttle extraction below approx. 2 °C, provide peak load.
• Measure temperature and salinity for a year; titanium for corrosion, screens and pigging for fouling, glycol intermediate loop for frost.