T🍅matonomics: Carbon offsets through heat reuse in Dutch datagreenhouses

Dutch startup BlockHeating opens its first commercial datacenter featuring heat reuse

Today, Thursday 24th of June 2021, marks the opening of a new datacenter in The Netherlands, by a small Dutch startup BlockHeating. As their name suggests, they are focused on reusing the heat generated by their datacenters, for example to grow vegetables like tomatoes 🍅 and cucumbers 🥒. This is done through co-location with Venlo greenhouses.

Like most resource intensive industries, the datacenter industry is under pressure to contribute in reducing Greenhouse Gas (GHG) emissions as agreed in the Paris climate accord. In response, all major datacenter operators (like Google, Microsoft, Amazon, Oracle) have pledged their support in various wordings —however, some questions about the effectiveness and concreteness of these commitments remain.

This is why small but essential examples like BlockHeating today deserve to be highlighted: Unlike most datacenter announcements in the news, they represent real concrete steps on a path towards true sustainability.

Natural gas in The Netherlands

Natural gas plays a big role in the energy market in The Netherlands. In Groningen (where I was born) we have the largest natural gas field in Europe, and for decades Dutch people have used natural gas to heat their homes and cook their meals; 90% of building heating and 40–50% of heat used in the industry comes from gas. However, due to recent negative effects — like earthquakes — attributed to the extraction of gas from the ground, it has been decided to stop gas production by 2022, and move away from gas as a source of energy.

Like gas, vegetables and other agricultural products represent a major export category for the Dutch economy. In 2020 these exports valued €95 billion, about 70% of which were produced in Holland. Due to local climate and land resource conditions, a good portion of these are produced in greenhouses; 90% of all greenhouses globally have Dutch origins.

Tomato biochemistry and optimal growth temperature

Like in all plants, tomato plant leaves perform photosynthesis — the biochemical process by which chlorophyll uses light energy, in combination with water and carbon dioxide (CO₂), to manufacture the sugar glucose that is vital to tomato plant and fruit growth.

Net assimilation in tomato plants at various sunlight and CO₂ concentration levels (higher=better yield) source

As illustrated by the graph (replicated from this paper), the efficiency of the photosynthetic process — and hence the fruit yield — is affected by a combination of factors, including sunlight intensity and the concentration of CO₂ in the air. To quantify: ‘normal’ outside air CO₂ concentrations are around 400–415 Volume Parts per Million (vpm), 1 vpm CO₂ corresponds to 2 mg per cubic meter and a sample tomato crop may assimilate 1 mg CO₂ per square meter per second.
Some growers apply “atmospheric fertilization” by artificially increasing CO₂ concentrations (to 1000 ppm for example), either continuously or varied between day and night.

Global monthly CO₂ levels as measured by the US NOAA

Based on scientific models the optimal growth temperature for tomatoes varies between 22℃ to 28℃; based on local weather data for Venlo (where the datacenter-greenhouse is located) this means yield can be improved all year round. Photosynthesis (including assimilation of CO₂) is accelerated by increased temperature, provided sufficient light, nutrients and water are available.

Average temperatures at the datagreenhouse site

Global Warming Potential (GWP) in the tomato production chain

Comparison of 100-year GWP for various production chains in different countries (source)

In a 2013 study the carbon footprint of various different tomato production chains over a 100-year period was analyzed; the “Conventional System 1” corresponds to a heated Venlo greenhouse, of the type that BlockHeating is supplying its heat to. The pink area corresponds to 848 grams CO₂ per kg of tomatoes produced over a 100 year period, due to the use of conventional heating solutions.

Similarly, a 2006 study in the UK shows that 97% of energy used for growing tomatoes (at the time) went into heating and lighting to extend the British growing season. Consequently, gas and electricity usage dominates the Global Warming Potential (GWP) for tomato production there, and significant gains could be achieved by reusing datacenter heat instead.

Replacing gas or electric heating with datacenter heat

1 m³ of natural gas provides about (1.8 Kg) 1,000 L of CO₂ when combusted and 1.4 L of water. In the US, electricity production uses 0.21 m³ gas per kWh (2020). If gas is used for heating, Dutch natural gas produces 33.32 MJ/Sm³ (standard cubic meter at 1 atm 15℃), given 1 BTU = 0.001055 MJ that converts to 31583 BTU per Sm³.

If we make some assumptions at this site a small greenhouse would require roughly 2.2m³ of Dutch natural gas per hour, to be heated from an outside 10℃ temperature to a more optimal 22℃ for growing tomatoes. A 20 kW electric heater could also provide this heat. In both cases, heat from servers could replace this gas usage either at the greenhouse, or indirectly at the electricity power plant — effectively reducing the total carbon footprint.

Sample dimensioning of a small Venlo greenhouse

Sample heating requirements calculation (source)

Conclusion

The datacenter industry is being asked to reduce its environmental impact. Heat produced by servers can replace the use of natural gas, either at industrial or residential consumption sites or indirectly at electricity power plants — thus directly and measurably reducing the global carbon footprint and contributing towards true net-zero emissions goals.

From what we can see, this is eco-systematic sustainability in practice — well done, BlockHeating!