Communal Heating and Hydrogen
The Logic:
- Hydrogen is inefficient compared to local heat pumps
- Hydrogen has the advantage of being able to deliver higher temperatures (Exergy)
Sizing heat sources can be roughly divided into 3 parts:
- 90% load. This is the hot water and normal central heating, as can be delivered by a heat pump running at 60C.
- 10% load. This is driven by central heating when it is very cold. It only happens for a few days or weeks a year, and accounts for only 10% of total load, but required temperatures higher than 60C.
- Redundancy. This is an oversizing factor there to allow for times when a heat source is offline (failed).
This is seen in the graph below looking at real loads for 2020. The Blue (DHW) and Orange (CH low) are driven by the heat pumps. The Green is delivered by hydrogen topping up heat pumps, as is redundancy.
The conclusion:
Hydrogen can form a critical role in communal heating by acting in a topping up boiler role, providing high temperature heat to satisfy load on the colder days.
When converting existing sites that run on gas boilers to renewables, the optimal approach would be to replace 1/3 with heat pumps and convert the remaining boilers to run on hydrogen to provide the top-up and backup roles.
It is important to note that even while boilers are still running on gas, the carbon savings are over 90%. The final 10% (the painful part) is where it will take a lot more cost and time, either replacing them all with heat pumps, or converting to hydrogen.
Therefore it makes sense to leave gas boilers in place until all sites are converted to 1/3 heat pumps, getting to 90% reduction in carbon for the least expense and time. Then focus on the the last 10%.
