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chimney retrofit air source heat pump   (+5)  [vote for, against]
retrofit air source heat pump to open fireplace chimney

There must be many thousands of old houses with open fireplaces and their associated chimneys, which however are no longer used as open fireplaces due to polllution or fuel availability or desire for on demand electric or fossil heating.

Proposed is a mass produced standard unit that can be dropped in to any normal open fireplace type chimney.

Cold end is mounted on the chimney pot, hot end is mounted in fireplace. Refrigerant pipes run down chimney space.

Could be mass produced to reduce production costs. Installation would be simple, requiring only climbing onto the roof and dropping the pipes down the chimney, and stuffing the gaps at both ends with something nice.
-- pocmloc, Oct 06 2021

Great idea as long as it comes with a training college so that tiny orphan children can learn how to crawl up the chimneys to service and repair the apparatus contained inside.
-- xenzag, Oct 06 2021


How will Santa Claus or Jack Skellington get past all that plumbing?
-- a1, Oct 06 2021


The bottom end could be made to work, there's a reasonable amount of volume to work with in the fire place. The top end, I don't think so. A chimney is designed for unidirectional flow of a modest volume of hot gas. As such it's a single tube in the 4-8" (100-200cm) diameter range.

Now look at the condenser of an AC unit as an example, it's much bigger and requires airflow through it. There's no way you'd be able to get a practical amount of airflow in, through and out of a heat exchanger in a space that was fundamentally designed for a different purpose.

Much easier and cheaper to use a mass-manufactured mini-split and make a reasonable effort to hide it.
-- bs0u0155, Oct 06 2021


Would air be flowing through the chimney or would it merely contain the refrigerant plumbing?
-- whatrock, Oct 06 2021


If the air is flowing through the chimney, it could be made to work, but with horrible efficiency. You could take air from inside the house, cool/heat half of it at the fireplace section, send the other half up the chimney over the upper half of the heat exchanger pair. This is sort of how the single-hose portable air conditioners work. But, by dumping half the air, it has to be replaced with outside air, which is hotter/colder than is ideal - hence, horrible efficiency.
-- bs0u0155, Oct 06 2021


Indeed. So in the former arrangement the outside unit is the weak point. A larger condenser, perhaps made to look like a large mushroom, perched on the chimney pot?
-- whatrock, Oct 06 2021


This idea is cool... as long as you are at the base of the chimney.
-- 2 fries shy of a happy meal, Oct 06 2021


//A larger condenser, perhaps made to look like a large mushroom,//

Exactly, there isn't the volume available to work with. Although I do like the mushroom form factor!

Not practical however, chimneys are already a bit of a structural nightmare, brick ones at least. They're a high surface-area/volume brick structure exposed to the worst of the elements and without warmth from use, they get a lot of freeze-thaw water damage. Adding a large heat exchanger would need the structure of the chimney to be checked, and then all winter it would be actively & cyclically cooling that same structure, probably covering it in condensed/frozen water - which then breaks off, slides down the roof and kills the window cleaner.
-- bs0u0155, Oct 06 2021


Kids these days: "I remember fondly the humming compressor and rattling refrigerant pipes of my grandfather's chimney. After hours of play in a winter wonderland, my sister and I would sit still with our backs to the supply vents and warm ourselves completely over the course of several additional hours."
-- Condiment, Oct 06 2021


Does it need an active unit at the top, or just a coil of pipes and vanes for the wind to flow over?
-- pocmloc, Oct 06 2021


[+] Good place to place a slighty modified standard unit. Pipe through brickwork and mount external unit on outside. With a few extra sensors and use/not use chimney air flow/temperature when advantageous.
-- wjt, Oct 23 2021


Like bs0u said, typically the coils need a lot of surface area to blow air across to remove that heat or cold. You've only got about a square foot or so of open area in a chimney so you'd really have to be sucking a lot of air in to make this work, you'd need a pretty powerful fan to get the CFM you'd need and it'd probably sound like a jet engine.

But bun for an interesting idea to look at.
-- doctorremulac3, Oct 23 2021



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