The Role of Sewage Thermal Energy Use (STEU) In Data Centers
How Can Data Centers Become Less Wasteful of Local Resources?
Data centers are a part of our modern life, a necessary component of our current infrastructure space. They have been around for a long time too, first referred to simply as Server Farms, then later The Cloud and now as AI. With each step comes the next level of development and as with most infrastructure, the NIMBY (not in my backyard) effect applies. People want the benefit of a specific asset but do not want it in their neck of the woods. One of the main reasons stated for opposition to its local development is that they use too much electricity and water. It is reasonable to expect a new infrastructure project to be a good neighbor but is it reasonable to expect the laws of physics to be abandoned? Hence the need for compromise and creative thinking. How can we make data center use less wasteful or at least more acceptable?
Water Is the Epicenter of Environmental Impact of Data Centers
To develop the framework in which to compromise, it important to know more about how the systems work and to clearly define objectives. The construction of data centers requires capital, which they have received, and to date they are performing in the financial space. This is not a reflection of the long-term viability of the ventures but clearly, they are currently able to pay for the water and electricity they use. This is having a measurable effect on the overall cost of electricity and the economy in general. They are also performing in their technical mission helping to fill the expanding need for such services. So, what remains is the environmental impact.
Not only do data centers use a lot of electricity to do their IT work, but they also need additional electricity to keep the equipment cool enough to operate and control humidity. What the facility does with that heat after it cools the servers is the concern in this post. Heat can be removed from the building cooling system via air or water. Water is 4,000 times better at heat transfer than is air, so as one might imagine, the cooling of data centers is a water centric process.
Evaporative Cooling Is Powerful, But It Permanently Consumes Water
In most cases the overall system cooling is achieved via the thermodynamically beneficial effect of evaporation. Cooling water by evaporation consumes a vast amount of heat, which is the objective of the system. It takes 970 BTU to evaporate one pound of water. If one were to heat one pound of water from 32 F to 212 F that would take 180 BTUs. Evaporating water consumes more than 5 times as much energy as it takes to heat it. However, once that water is evaporated it is discharged into the atmosphere and blows away. Evaporative cooling is powerful, but it permanently consumes water. If water is of value to the community, then evaporative cooling becomes a conflict point.
Evaporative cooling consumes even more water than it takes to evaporate the waste heat. The cooling system needs to discharge a certain amount of water (blow down) to keep the water quality of the cooling stream in the appropriate range. Therefore, some water conservation methods are focused on reclaiming and treating the blow down water so that less water is used in the system overall, but evaporation still takes place.
One could choose to find an alternative supply of water other than the local potable water utility. If that source is ground water, then the data center is still pulling water out of the local potable water supply. However, on could approach the local wastewater authority and their plants, what are often referred to a water resource recovery facility (WRRF). The effluent of these WRRFs can be treated to a high enough quality to be used as the cooling water. In this scenario, the WRRF becomes the source of cooling water reducing stress on the local potable water supplier. Water is still being consumed (discharged as vapor to the air) just not potable water.
Data Centers & Thermal Energy Network Utilities Working Together
Better yet, the waste heat can be discharged into a sewer by heat exchanger so that evaporative water is not needed. A flowing sewer has a tremendous amount of thermal capacity, both to give up heat and to accept heart. Again, water (sewage is over 99.5% water) is 4,000 times more effective at heat transfer than air.
For example, at the Dam Neck Naval Annex in Virginia Beach, their data centers add heat to a base internal meso-temperature loop. This loop provides heat to all buildings, year-round, with each building having its own heat pump to remove heat from the loop. However, in the summer and when there is too much heat, it dumps the excess in Hampton Roads Sanitary district’s Atlantic plant effluent. The plant effluent is the systems thermal sink. There must be sufficient flow of wastewater to absorb this excess heat.
A Framework of Compromise & Creative Thinking
The highest value use of data center waste heat is to supply a local heat loop so that excess heat could be used in a Thermal Energy Network (TEN). In this way a separate third party TEN utility could make beneficial use of that energy selling it as a method to help people reduce their carbon footprint and in many cases helping the local building stock electrify. The main reason this is not happening is that the operators of data centers are focused on meeting a growing demand under high stakes pressure. While third party TENs, with less access to capital, are looking to be profitable over the long run while providing a service to a community.
Considering the use of sewage thermal energy will increase the acceptance rate of data centers and allow for their inclusion in more densely populated areas, where there are large sewers. Developing a relationship with the local wastewater utility and the inclusion of a Thermal Energy Network will proved the framework of compromise.
Dedicated to Advancing the Understanding & Application of STEU
The Sewage Thermal Energy Network (STEN) champions this innovative approach. STEN connects a diverse group of professionals – including engineers, scientists, policy experts, and civic leaders – who are dedicated to advancing the utilization of sewage thermal energy. As the leading network in this nascent field, STEN fosters collaboration and knowledge sharing to drive the adoption of STEU practices, contributing significantly to sustainable urban development and environmental stewardship. We are the premiere professional network for practitioners and policy advocates who see the potential for sewer thermal energy recycling. We facilitate collaboration between developers, municipalities, and academic researchers, fostering a network that supports public education and leads progress in this area.
