A heat pump could win as the best HVAC technology, though a better drilling for ground-sourced ones. Just a shallow drilling (up to 100m) that works in retrofit mode, such as drilling from the basement, would be a great upgrade: - No outdoor unit that looks awful in many settings - works well, even in the coldest winter, without a spike in electricity usage, COP 5 - very reliable with long durability - super quiet, n…
Drilling only works if you have access to a garden where to drill. Any kind of apartment has to use the outdoor unit
If you're building the apartment building you have the choice to drill for the entire building, and the number of units that benefit mean this is much more cost efficient than with single family homes.