Sea water district cooling feasibility analysis for Hawaii [pdf] (2002) | Hacker News Reader

Sea water district cooling feasibility analysis for Hawaii [pdf] (2002)

energy.hawaii.gov

I've read about this before when Toronto was implementing a system like this. The City of Toronto cools a large portion of it's downtown office towers using this method. They draw cold water from deep in Lake Ontario to be pumped into chillers to cool the office buildings. Seems to be environmentally friendly and cost efficient.

A couple of links:

https://www.acciona.ca/projects/construction/port-and-hydrau...

https://www.toronto.ca/community-people/get-involved/public-...

Sorta. They run heat exchangers between the in-bound municipal water and loops that go to the office buildings.

So it helps with some eco-effects (ie: there’s no dumping of the heated water), but everyone’s municipal water is a bit warmer in summer. I don’t think the effects of that have been calculated. Can offset water heating a bit; but other office towers use that water for their a/c cooling needs.

They deepened the water intake too, so it definitely means colder tap water in winter too, which residents mostly have to heat up inefficiently.

Is there a limit how hot or cold your waste water can be?

In many eastern europe cities heating is centralised and uses quite expensive wood or oil burners. Wondering if extremely deep geothermal bores could serve 200-500k people.

It’s kinda hilarious (to people living in areas with actual seasons) to hear about summer and winter in Hawaii. Based on the temp averages I see on weather.com, there is some variation. But how does it actually feel? Does “Hawaii winter” feel like actual different season or is it just “slightly less hot summer”/every other day?

Temperature measurements are usually counted as above ground, in shade measurement for the time/date given. In Hawaii the difference in summer/winter is in number of hours of sunshine (due to cloudy/rainy season), sun altitude at solar noon (due to position in northern hemisphere), and total numbers of daylight hours (same thing, due to position in northern hemisphere).

All these factors mean that during summer you need to cool offices in Honolulu more than in winter, even though that the measured difference in temperature at noon can be minuscule.

It feels different to us in Hawaiʻi, mainly due to increased rainfall.

Days are shorter in the winter and the weather patterns are different. Summer is much hotter and the trade winds blow stronger. Winter storms come from north of japan and bring north swells. In the Summer storms near Australia send swell up from the south. And it rains more in winter as another hner indicated. I recall it rained for about 3 weeks straight one year.

It's relative. If you step off a plane in winter you might think the 64°F night-time temp is downright balmy. But if you've lived there for long enough it's "freezing" and requires a nice warm sweater.

But yeah, most freestanding houses have neither, and need neither active heading out cooling (aside from a ceiling fan for circulation).

For the last 30+ years though, it seems like there's been an importation of building design that rely upon air conditioned spaces (concrete with sealed windows basically) where buildings from mid century would have ensued outdoor access on two sides with louvered windows for cross ventilation.

I wonder if this deep water cooling proposal is basically an attempt to mitigate the rather short-sighted move to these more energy consuming buildings and the realization that they are needlessly expensive to operate and not in line with the community's purported environmental ideals.

> deepened the water intake too, so it definitely means colder tap water in winter

Would it be so expensive to have two intakes?

If they considered the (mostly negative) externalities I described, a valve could've been a good idea. But getting people water a few degrees warmer in winter saves somebody else money, not them.

Maybe collecting deeper water improved water quality in some other way. Dunno.

I just don't understand why Hawaii government has been so slow to mandate the most economically-net-positive renewables, given their astronomical electricity costs (old, shipped-in fuel, diesel-fired generators).

Solar hot water, solar PV, wind. Stop being held over a barrel with these electricity costs. They live in the most conducive place for it in the world, yet don't take advantage of it, really.

Minor quibble: It’s more efficient to use a heat pump water heater, and max out your PV solar instead of splitting PV solar with solar water heating.

Is it? Solar PV overall efficiency is probably 15-20% of the incoming solar power. While, a solar thermal hot water system can reach 50% or higher efficiency, even accounting for storing the hot water for several hours.

Solar thermal also just requires fairly cheap mirror like surfaces, while solar PV requires semiconductor chips.

Heat pumps are at the 400% efficiency level so by your numbers they're already ahead. And PV has other advantages. It's easier to install since it doesn't require specific tubing and the panels are much lighter. The energy is useful for other things when you don't need as much hot water. And efficiency goes up in winter because PV is more efficient in the cold whereas efficiency of thermal solar goes down as you need to heat the panel before heating the water. It will depend on your local PV and heat pump costs but thermal solar seems less and less relevant these days.

AIUI, ground source heat pumps get really expensive when the ground is really hard. A reasonable proxy is “do your neighbors have basements?” If the answer is “no”, then it’s probably because digging is more trouble than it’s worth.

Efficiency is still good for air source heat pumps IIRC. They only go down to 100% at well below freezing which is probably not a problem in Hawaii. Ground source only requires a small hole though, of the kind that is done for water. I'm in a granite rich area where basements are very rare but water wells are very common and reasonable cost to drill.

Mitsubishi air source heat pumps maintain ~79% capacity at -22F (check with your local Mitsubishi diamond split dealer for deets).

> “do your neighbors have basements?” If the answer is “no”, then it’s probably because digging is more trouble than it’s worth.

Basements are popular in cold climates because footings already need to be dug several feet down to get below the frost line. In warmer areas, basements are uncommon even if digging is easy.

Oh, well I mean for simple cheap residential don't-have-a-lot-of-money-to-spend, a do it yourself hot water solar system is just about the cheapest, easiest thing you can do, right?

> I just don't understand why Hawaii government has been so slow

Island time is a real thing. And politics in Hawaii takes nepotism and "good old boys" networks to the next level. Things are the way they are because the people in charge are happy with it.

HART (the light rail system they're building) is a complete disaster, for the same reasons.

I can't see the government there being able to handle much of any major infrastructure project. The airport expansion is moving at a glacial pace as well. And it's a miracle the H3 ever got built.

No need for mandates. Power and fuel are expensive so people already have a strong incentive to invest in renewable power and efficiency improvements.

Out of state folks are investing into 8,000 acres of solar plant in central Ohio. My guess is that there are material administrative impediments to the process rather than lack of demand.

As is usually the case, it's complicated.

The government has actually taken steps to push us down that road by mandating that all generation is renewable by 2045. Of course that's easy to say and harder to do, but I'm not sure it should be up to the government on how we get there.

The entity with the most responsibility to get there is HECO, which has a bit of a mixed record.

On one hand they have been pretty good about encouraging customer generation with net metering, and later grid supply options. Unfortunately there is a bit of an engineering problem there as we have pretty much reached the saturation of customer solar such that in the middle of cold sunny days, there is more electricity being produced than consumed (see duck/nessie curve). This would sound like a good thing, but with an extremely old grid and no utility level storage, it's kind of not.

A more reactive utility perhaps would have done a better job upgrading the grid to allow for distributed generation, but HECO spent the better part of the last 5 years trying to get themselves sold to a mainland utility to drive returns to shareholders instead of placing institutional focus on solving current or future problems for ratepayers. Serving two masters, etc.

Kauai has a much more interesting situation as their utility went through that whole sale to the mainland thing in the 90's, which failed and provided the opportunity for the ratepayers to buy the owners out and created a cooperative utility. I don't live there but from the outside looking in it looks like they are being much more proactive about renewables and more importantly, storage.

Absent some kind of massive game changer in wave or wind generation, the whole game is really storage. I know a lot of people who would love to install solar, but HECO is already at max capacity absent a way to store electricity at scale.

Finally the part that gets talked about the least is economic inequality. Hawaii's real estate is expensive, but it is driven by investment from outside the state, making it almost impossible for people who live here to afford homes. That interacts with the energy piece because you have to be a homeowner to benefit from solar, so solar contributes to wealth inequality as people who are fortunate enough to own homes also reap the benefits of government subsidies and cheap electricity, while people too poor to own homes are left paying the retail rates. And this is before we even get into the distortions of behavior that net metering encourages when you treat a kwh of solar in the day as equal to a kwh of petroleum at night.

Cornell University has a similar cooling system using cold water from Cayuga Lake.

https://fcs.cornell.edu/departments/energy-sustainability/ut...

Skytherm roof is better. No need to pump sea water or lake water just put the water in containment on your roof and uncover it as you want solar heating (winter daytime), radiant cooling (summer nighttime), or cover it if you want thermal capacity heating (winter nighttime) or thermal capacity cooling (summer daytime).

http://www.solarmirror.com/fom/fom-serve/cache/30.html

(October 2002)

Any more recent developments on this front?

Since then there's been a lot of wind farms installed in Hawaii and most homes have solar powered water heaters (from personal observation). Don't know anything about the sea cooling concept but it seems viable and for long time cornell has done it or at least on a tour they said they did https://fcs.cornell.edu/departments/energy-sustainability/ut...

https://www.ithacajournal.com/story/news/local/2015/10/02/co...

Interesting..

Ah here is the older one I remember from a tour https://fcs.cornell.edu/departments/energy-sustainability/ut...

Talking to locals in Maui most aren’t very happy with the wind farms. They’re considered an eye sore and they were sold under the pretense of lower electricity bills which never happened.

Looks like a deal was "reached" in 2018 [1], but just this week "Honolulu Seawater Air Conditioning to end development after 15 years" [2] and their website is now a scam. The Wayback Machine has the original [3].

[1] https://www.bizjournals.com/pacific/news/2018/10/09/hawaii-f...

[2] https://www.bizjournals.com/pacific/news/2020/12/19/honolulu...

[3] http://web.archive.org/web/20200929031903/http://honoluluswa...

How far is it practical to move hot/cold water?

Could a big pipeline (say 5 yards diameter) be built between the north and south of the US to bring icy water for cooling in Texas and take back hot water to heat detroit?

Pipes could be tapped in any place for water too, ending per-state water shortages while other states have flooding...

you can move water with canals just fine, but it won't be cold any more

It would be interesting economics to revisit this now with much lower interest rates, higher labour costs and very different plant costs due to changes in technology and lower cost manufacturing of some of the components.

Millions of kWh. Aka, many GWh. Why call it the former instead of the latter?

I assume it makes it relatable to people who are accustomed to seeing kWh on their electric bills.

Bills for thousands of cents.

That's what the submitter chose as a submission title. The document's title is "Sea Water District Cooling Feasibility Analysis for the State of Hawaii".

If you want to normalize the SI units, you could also replace "many GWh" with "many TJ".

I also think we should say the moon is 384 Mm instead of 384,000 km. Mega meters are awesome, we should use them more. And the earth sun distance is 150 Gigameters.

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