City block sized heat pump - also wondering if there are problems with heat pumps - as in causing problems in the natural world

[Montero]

The enormous heat pumps warming cities

From New York City to rural Cornwall, communal heat pump networks could be the answer to decarbonising heat in both city high-rises and other hard-to-heat homes.

www.bbc.com

So great idea in theory to use heat pumps to heat in winter and cool in summer and therefore would even be putting the heat back that you take out.
Do note that you have to insulate well first - and that is not something that is exactly happening with any alacrity at present.

I did notice the line about all the years of sunshine it had taken to warm the earth and was then thinking, so is it a good idea to remove it? Will trees with deep roots suffer if the ground gets a lot colder? Could something else go wrong?

 

[Wayne Mack]

This is an interesting proposal and may work well in certain areas. I wonder about locations that either have considerable bedrock and those near sea level. A line, though, the gave me pause and seems to challenge the idea that this approach would reduce the cost to individuals was, "Finally, this heat is transferred to water, which is pumped through a house's specially upgraded pipes and radiators."In the US, I believe most houses rely on forced ari heating rather than radiators.

 

[Montero]

This is an interesting proposal and may work well in certain areas. I wonder about locations that either have considerable bedrock and those near sea level. A line, though, the gave me pause and seems to challenge the idea that this approach would reduce the cost to individuals was, "Finally, this heat is transferred to water, which is pumped through a house's specially upgraded pipes and radiators."In the US, I believe most houses rely on forced ari heating rather than radiators.

Huh. Some houses in the UK had air heating but it was never very popular. However from what I've read about using air source heat pumps, for those that means replace all radiators with much larger ones as you will be operating with lower temperature heating water so need a wider radiant area.
On the other hand, with air heating, the air has to be heated somewhere, so maybe that is where the adaptation is made. Don't know enough on the details to be sure. It is interesting to work through the ramifications though.

 

[Dave]

Cities already have different microclimates - they can be 3 or 4°C warmer than the surrounding area. This is comfortable for us in the winter, but not so comfortable in the summer. On an even smaller scale, depending on their orientation, streets with tall buildings can either become canyons that are wind tunnels or else harbour stale polluted air with no movement. The buildings shade the streets below too, but not in the way that a tree canopy would. Water is drained away quickly from the hard surfaces. So, they are hot, dry, but sunless places, inhospitable to living things, unless we add trees and parks, green walls and green roofs.

Certain parts of North London with an ethnic population from warmer climates, have air conditoning units on every residential house, as well as on offices and shops. Walking by on the streets outside, you can really feel the heat being pumped out of these houses during the summer, and it is quite uncomfortable on some of the already hot days that we've had in recent years. I expect that even more people will get air conditioning for their residential houses in the future, due to rising summer temperatures, working from home, and higher summer temperatures over a longer period of time.

So, yes, higher temperatures in built-up areas do affect the climate in a bubble surrouning them, and while it is nothing new, heat pumps will continue to do that. They do, however, just like the air conditioning units, simply move the heat around, rather than releasing chemically stored energy. That has to be a good thing, but if you mean it isn't truely renewable energy, well it is being "collected from renewable resources that are naturally replenished on a human timescale" and so technically it is.

Also, the "city block sized heat pumps" that I have heard about are using warm water from flooded coal mines in places like Durham. I assume that the Cornish example in the report is using Tin mines. So, the heat is being taken from deep underground, much deeper than any tree roots. I can't see that being a problem. The idea is more like having a very low energy geothermal plant.

 

[Montero]

OK, really deep sounds fine. Though the cheaper option with the wide area of near surface trenches and pipes still concerns me as to the impact of cooling soil and sub soil will have on the environment. Including earthworms - just about to post an article on earthworms great importance to the environment.

 

[Swank]

Hot (and cold) water to forced air systems exist.

You don't have to worry about the earthworms in the top soil since cities don't have much top soil. Just do your heat exchange under buildings and pavement.


The natural world is having problems, and it isn't from heat pumps cooling it too much.

 

[Wayne Mack]

I assume that one of the adaptations that would be needed to convert to a forced air system would be to have a fan running for continuous air circulation. The article says the system heats glycol to 122F / 50C. I am not certain whether there would be any need to use water as an intermediary, perhaps the air could be heated directly. By comparison, a gas furnace burns at 3,560F / 1,960C. With a nominal target of 68-72F / 20-22C, a heating element of 122F / 50C would need to exchange air more frequently.

I don't think this would necessarily be a problem, I just expect it would mean that a forced air system would likely have air vents blowing near continuously, though the air flow when running might be lower--a calm breeze rather than a sudden burst.

 

[Montero]

Hot (and cold) water to forced air systems exist.

You don't have to worry about the earthworms in the top soil since cities don't have much top soil. Just do your heat exchange under buildings and pavement.


The natural world is having problems, and it isn't from heat pumps cooling it too much.

Yes, that is true in cities. I was also thinking wider than just cities and the general case of how ground source heat pumps are deployed, including outside of cities.

I assume that one of the adaptations that would be needed to convert to a forced air system would be to have a fan running for continuous air circulation. The article says the system heats glycol to 122F / 50C. I am not certain whether there would be any need to use water as an intermediary, perhaps the air could be heated directly. By comparison, a gas furnace burns at 3,560F / 1,960C. With a nominal target of 68-72F / 20-22C, a heating element of 122F / 50C would need to exchange air more frequently.

I don't think this would necessarily be a problem, I just expect it would mean that a forced air system would likely have air vents blowing near continuously, though the air flow when running might be lower--a calm breeze rather than a sudden burst.

That's interesting. Maybe also increase the area of the heat exchanger, since one of the adaptations for a hot water system to move to a heat pump source is to make the radiators bigger.
Query @Wayne Mack - do you know if there is any drying component as part of hot air heating systems? I live in a damp part of the UK, which can be pretty humid, and the temperature in the house can feel cold in winter, when the thermometer says it should be fine - which is time to run a dehumidifier. So another way for a house to feel warmer in a damp winter, or indeed cooler in a hot humid summer, would be running the air supply through a dehumidfier as well. (Though at that point, if it is one with a refrigerant coil on it, you are using more electricity on that.)

I just went looking for a building adaptation I remember hearing about maybe 20 years back but it doesn't seem to be current anymore - which is to have actual water tanks built into the foundations of the house, to be a localised heat store/heat sink. Everything these days seems to be big insulated metal tank heat stores.

 

[Swank]

I assume that one of the adaptations that would be needed to convert to a forced air system would be to have a fan running for continuous air circulation.

The "forced" in forced air is the fan.

Yes, that is true in cities. I was also thinking wider than just cities and the general case of how ground source heat pumps are deployed, including outside of cities.

It is done on the home scale using deep wet wells to draw heat off and dump it back in during AC summer months. Some systems use swimming pools for AC, but the pools can get too hot. Water tanks in the house don't have enough capacity for much heating or cooling. The tank would just eventually freeze.

 

[Montero]

@Swank - yes, the modern heat store tanks aren't that big and also don't come cheap. I did also read about building big tanks under the foundations, or it was possibly also a deep gravel bed. It is one of those faded memories about a development that was definitely using a special structure built underneath a house for heat storage, and I think with insulation as well as the insulation of the soil. Can't currently find it.

 

[Yozh]

There’s a very large-scale cooling system for downtown Chicago that’s also using big tanks along the river and glycerol pipes. It’s decades old. I don’t know why it’s just used for cooling and not heat.

The ice machine that cools Chicago’s skyscrapers

 

[Cthulhu.Science]

Danish Esbjerg puts trust in one of world’s largest heat pumps
Sustainable district heating spells the end for coal-fired power plant and serves 100,000 households

Denmark is a leader in regional heat pumps. They are also a leader in garbage incinerator plants, often combining the two.
Number of heat pumps in operation in Denmark from 2013 to 2020