Heating Emergency Power System Engines with Heat Pumps (Levi J. Westra)

Overview

This document is a case study written by Levi J. Westra and published in 2025 by the iMasons Climate Accord (Infrastructure Masons). It is a field measurement and verification study of replacing electric-resistance engine block heaters on standby generators with air-source heat pumps, keeping the original heater as an auxiliary.

The rationale is that NFPA 110 requires emergency power to start, reach speed and take load within 10 seconds, so engines are kept warm by block heaters. Block heaters are typically 1-9 kW each, with multiple heaters on large engines; heat loss scales with block surface area and the block-to-ambient temperature difference. The study aims to cut the energy cost of this continuously running load.

The method was as follows: five sites in and around Spokane, WA, including two data centers, with 750 kW to 2.5 MW gensets were metered before and after. CT data loggers on the heater circuits, enclosure temperature logging and energy binned against outdoor temperature were used, and results were extrapolated to a typical meteorological year with TMY3 data. As a result, block-heating energy fell by an average of 78%, equal to 22,463 kWh per year per generator (range 11,703-36,682 kWh/yr).

The average saving equals about $3,217 per year for a US commercial customer and 9.8 t (gas grid) to 23.5 t (coal grid) of GHG avoided per generator. Air-source heat pump performance drops below about 40 F, where the retained OEM heater is staged on, and the arrangement gives effectively N+1 heating. Limit: five sites and one climate region; the results should not be carried directly into other climates.

Key points

1. NFPA 110 requires emergency power to start, reach speed and take load within 10 s, so engines are kept warm by block heaters.
2. Block heaters are typically 1-9 kW each, with multiple heaters on large engines.
3. Heat pump retrofits cut block-warming energy by an average 78%, or 22,463 kWh/yr per generator (range 11,703-36,682 kWh/yr).
4. Average saving equals about $3,217/yr for a US commercial customer and 9.8 t (gas grid) to 23.5 t (coal grid) of GHG avoided per generator.
5. Air-source heat pump performance drops below about 40 F, where the retained OEM heater is staged on; the arrangement gives effectively N+1 heating.
6. Method: CT data loggers on heater circuits, enclosure temperature logging and binned energy vs outdoor temperature extrapolated with TMY3 data.
7. Five sites in and around Spokane, WA, two of them data centers; 750 kW to 2.5 MW gensets.

Using it in design

• Include generator auxiliary loads (block heaters, battery chargers) in the parasitic load and PUE calculations.
• Add a 'heaterType' option (resistance vs heat pump).
• Use about 22 MWh/yr per genset baseline and about 78% saving as default estimates for cold-climate sites.
• Document heating redundancy when retrofitting heat pumps by keeping the OEM heater as backup.

Who should read it

Engineers designing and operating generators and standby power systems, and operators seeking energy efficiency and carbon reduction.

Related standards

• NFPA 110

Publication details

Authors

Levi J. Westra

Publisher

iMasons Climate Accord (Infrastructure Masons)

Year

2025

Document language

English

Source type

Industry body

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation