Waste Heat Recovery: Waste heat can be considered as either low grade (<100°C), medium grade (100°C--400°C) or high grade (>400°C).
About half of industrial process heat is >400°C.
[su2021multigrade] puts the thresholds at 230°C and 650°C, and puts fuel cell, cement and steel industries into the high-grade category; glass, electricity generation and automobile transportation are in medium; a further six are in the low-grade category including food and petrochemicals. This paper describes a multitude of recovery theoretical and deployed mechanisms from sewage (evaporation condenser) to cement (flue gas).
It is often the case that within one manufacturing process plant, eg chemical engineering, there are places that need heating and others that need cooling. With care these can be coupled ("process integration") to minimise external energy demands and waste emissions.
One of my banking clients needed no heating for the human occupants in winter because it was able to reuse waste heat from the servers in the same building; the building did require cooling in summer however.
At home I have MHRV (Mechanical Heat Recovery Ventilation) that recovers about half the heat from exhaust air in the bathroom and kitchen. Notable is when very humid air from the bathroom has the moisture's latent heat recovered and water drips outside.
District heating and cooling schemes can share thermal flows between buildings close by.
Winning solution
The team that I was in won the group challenge (ie planning for better use of 'hyperscale' data centre waste heat), mainly by making use of a 60°C stream from liquid cooling for domestic space heat and DHW, ~10k+ homes in heating climates for each 100MW of data centre power demand, tacking fuel poverty and earning a social licence to operate.
Ideal Job
We were also asked to bring along a copy of a job advert for your ideal job (either now or in 5 years' time).
Mine would be something like:
Fractional CTO/CSO/CEO of start-up with climate impact, preferably in the energy efficiency space, maybe distributed demand-side response at scale, eg millions of participating end-points or more.