The passive house community could have saved a lot of time had they appreciated the influence of thermal effusivity sooner. The thermal mass doesn't contribute to regulating comfort over diurnal scales if there's insufficient area or if it's not conductive enough. This becomes obvious with highly variable solar gain or occupancy rates. Passive thermal regulation of a higher density, more conductive, internal lining systems, on a lightweight, highly insulated, timber frame structure, would contribute more to comfort than having a less well insulated mass wall system with a typical paper faced gypsum. Beyond that, you need active systems. There are some fascinating properties of thermal storage that make it really compelling for larger deployments: - The surface to volume ratio improves with scale, which translates to better cost per unit storage. - Heat loss is proportional to surface area, so it becomes more efficient at storing heat over long durations at scale. - When the full capacity of the storage system is not required, heat can be stored at lower temperatures using the full volume of the storage system, so the heat pump is more efficient and higher power output - meaning the cost of the stored energy is lower (unlike batteries where the charge state doesn't influence the cost of the energy.) - Water can be used as a storage medium and a working fluid, allowing direct mass transfer for efficient, high power, heat exchange. The problem is that the heat pump requires higher power output to exploit super off-peak periods of electricity. We still design heat pumps to meet peak instantaneous loads, which will be much lower than the power outputs required to store heat in advance to utilized peak PV or super off-peak rates on a variable tariff. This makes air sources more difficult to justify. We'd need an environmental source of heat to have their own TES, with liquid to liquid heat pumps running off water sources, or geothermal, or some hybrid solar thermal assisted reservoirs. Then there's the temperature range you can satisfy with a single heat pump refrigeration cycle, CO2 systems have a naturally high range, but perhaps cascade heat pumps would be better. Then there's seasonal variability in heating and cooling, I haven't seen thermal stores that can switch from heating in one season, to mixed heating and cooling in the shoulder seasons, to cooling only in summer. If anyone finds are good system design, let me know. E.G. Many configurations. I like Harvest Thermal's approach with C02 heat pumps. But there's also interesting liquid to liquid systems out there too: hydrosolar.ca/collections/liquid-to-water-geothermal-heat-pump-1/products/liiquid-to-water-dc-inverter-heat-pump-geo040v1lm-40-mbh-131-f-hot-water Case study with air source, PVT and high temp solar thermal: hydrosolar.ca/blogs/case-analysis/living-off-the-grid-with-solar-and-air-to-water-heat-pump
Thank you for sharing all this great data! Sure gave me a few more things to ponder, but I am also confident that I am on the right track.
The passive house community could have saved a lot of time had they appreciated the influence of thermal effusivity sooner. The thermal mass doesn't contribute to regulating comfort over diurnal scales if there's insufficient area or if it's not conductive enough. This becomes obvious with highly variable solar gain or occupancy rates.
Passive thermal regulation of a higher density, more conductive, internal lining systems, on a lightweight, highly insulated, timber frame structure, would contribute more to comfort than having a less well insulated mass wall system with a typical paper faced gypsum. Beyond that, you need active systems.
There are some fascinating properties of thermal storage that make it really compelling for larger deployments:
- The surface to volume ratio improves with scale, which translates to better cost per unit storage.
- Heat loss is proportional to surface area, so it becomes more efficient at storing heat over long durations at scale.
- When the full capacity of the storage system is not required, heat can be stored at lower temperatures using the full volume of the storage system, so the heat pump is more efficient and higher power output - meaning the cost of the stored energy is lower (unlike batteries where the charge state doesn't influence the cost of the energy.)
- Water can be used as a storage medium and a working fluid, allowing direct mass transfer for efficient, high power, heat exchange.
The problem is that the heat pump requires higher power output to exploit super off-peak periods of electricity. We still design heat pumps to meet peak instantaneous loads, which will be much lower than the power outputs required to store heat in advance to utilized peak PV or super off-peak rates on a variable tariff. This makes air sources more difficult to justify. We'd need an environmental source of heat to have their own TES, with liquid to liquid heat pumps running off water sources, or geothermal, or some hybrid solar thermal assisted reservoirs.
Then there's the temperature range you can satisfy with a single heat pump refrigeration cycle, CO2 systems have a naturally high range, but perhaps cascade heat pumps would be better. Then there's seasonal variability in heating and cooling, I haven't seen thermal stores that can switch from heating in one season, to mixed heating and cooling in the shoulder seasons, to cooling only in summer.
If anyone finds are good system design, let me know.
E.G. Many configurations. I like Harvest Thermal's approach with C02 heat pumps. But there's also interesting liquid to liquid systems out there too: hydrosolar.ca/collections/liquid-to-water-geothermal-heat-pump-1/products/liiquid-to-water-dc-inverter-heat-pump-geo040v1lm-40-mbh-131-f-hot-water
Case study with air source, PVT and high temp solar thermal: hydrosolar.ca/blogs/case-analysis/living-off-the-grid-with-solar-and-air-to-water-heat-pump
V2B, or Vehicle-to-Building is an interesting concept.