Lachlan's avatar@lachlanjc/edu
All Energy

Reflection: Vaclav Smil’s Energy Ch 5 & 6

A few years ago, my parents switched my house to electric heat pumps, away from a fossil gas furnace with an off-the-charts low level of efficiency. My room has a Mitsubishi MSZ-GL Wall-Mounted Indoor Unit, which I just looked into the energy usage of, and didn’t know any of the terms used to rate heat pumps:

  • Seasonal Energy Efficiency Ratio (SEER) of up to 24.6. This is the ratio of the total heat removed from the conditioned space during the annual cooling season divided by the total electrical energy consumed by the air conditioner during the same season.
  • Heating Seasonal Performance Factor (HSPF) of up to 12.8. This measures the efficiency of air source heat pumps—the ratio of heat output (measured in BTUs) over the heating season to electricity used (measured in watt-hours).
  • Coefficient of Performance (COP) of up to 4.44. This is the relationship between the power (kW) that is drawn out of the heat pump as cooling or heat, and the power (kW) that is supplied to the compressor.

It’s hard to find exact energy consumption data, since there’s a range of outdoor units the indoor unit can be paired with, but the HSPF gives a sense. The unit’s capacity is 6,000 to 24,000 BTU/H, so at 6000 BTUs of output, 468.75 watt-hours are used, or 1.69 MJ. At 24000 BTU/H, that’s 1875 watt-hours or 6.75 MJ (which costs 40¢ in NYC). The energy bill I brought into class is 392 kWH, for reference.

Smil’s predictions and projections in the final chapter have overall aged well—though change to “the way things are” has arrived sooner than he expected in his writing. His desire for “competitive and reliable PV would be a most welcome break-through” came true thoroughly, with the cost of new solar oftentimes undercutting the operation of existing fossil fuel projects around the world. His projections of hydroelectric ring true, since little has changed about hydroelectric in the last decade; if anything, we understand the damaging local biodiversity/land-species interactions better. On nuclear, “what has to change is the public acceptance of this, potentially risky, but very rewarding, form of electricity generation,” remains the case. The current state of nuclear is mixed: while major construction projects are not starting, seemingly every month there’s a nuclear plant shutting down, being restarted, or funding. Biden’s DOE created a $1.2B fund to keep unprofitable nuclear plants running, $150M for R&D, and other funding programs. We haven’t faced the one-day “true global warming shock,” but there’s recognition nuclear is a reliable low-carbon energy source.