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Comment by Cthulhu_ | Hacker News Reader

I'm still of the opinion that a dial works best. Especially in modern homes (in Europe at least), there seems to be a school of thought that you should just leave your thermostat at the same temperature at all times - the theory being that warming up a cold house in the morning costs more energy than maintaining a stable temperature.

Anyway, my ideal setup would be to install 'smart' thermostat taps on every radiator in the house, either manually turn them down when you're not in the room or have them automatically detect activity or open windows and adjust accordingly. But each one has the authority to trigger the central boiler if needs be, instead of only the master thermostat in the living room.

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> the theory being that warming up a cold house in the morning costs more energy than maintaining a stable temperature

This is only true if the heating happens quickly and the system is less efficient when heating quickly. Otherwise, this doesn't make sense from a physics standpoint. A temporarily lower temperature differential means less kWh of heat lost.

This is a whole research topic, my PhD in fact!

FWIW I run my heat pump intermittently and with locally-smart TRVs that get to call for heat centrally, and a weather compensation only flow temperature curve, and it WORKSFORME!

https://www.earth.org.uk/heat-pump-16WW-control.html

I enjoyed reading this, thank you.

\o/

Fascinating read.

Certainly feels like I'd need PhD from it to successfully install, modify, calibrate and run the installation until its fully adjusted, for the peak comfort and minimum cost/dirty energy use.

I am putting my efforts into making that not be true, at least for something "close enough" to peak comfort/efficiency/whatevs for any nominal shortfall not to matter in real life.

The obsessives amongst us can continue to tweak if we wish...

"Quickly" implies higher power which will make the air around radiators warmer than a slow heating.

The losses are proportional to the temperature differential between outside and inside.

So you should have somewhat higher losses from the hotter air streams from the radiators passing the windows.

Dunno about magnitude though.

Heating systems generally are more efficient when they need to output less power. Whether that cancels the increased heat loss seems to be a question that can’t be answered in general.

I think that maintaining a stable temperature means warm walls/floors/furniture and potentially cooler air temperature, as opposed to a cold house with intermittently warm air. Most people can feel comfortable at a lower thermostat (air) temperature if the walls etc are warm due to maintaining a stable temperature. I don't have calculations or references, YMMV.

>Otherwise, this doesn't make sense from a physics standpoint. A temporarily lower temperature differential means less kWh of heat lost.

This topic comes up anytime thermostats and heating are mentioned. The physics arguments only makes sense if you don't care about comfort. Most people would rather optimize for comfort with some energy/cost savings if possible and the physics folks seem to not care about comfort at all.

> the theory being that warming up a cold house in the morning costs more energy than maintaining a stable temperature

I've heard this theory a lot too, but it doesn't match with physics. A warm house loses more energy than a cold house, due to a higher temperature difference allowing easier heat transfer. So in most homes, with radiators and high temperature CV, it's way more efficient to just turn it off when you gone.

One exception is when you have a very well insulated house, combined with floor heating and a very efficient, low temperature heat pump. In this case, it takes a lot of time for temperature to move in the house and it's already incredibly efficient.

It does match physics if you consider other factors. Apart from the heat pump scenario, this statement can also be true when you have condensing boilers (and okay-ish insulation)

The reasoning: when you heat up the house, then your boiler needs to produce constant high-temperature water. When you keep the house at the same temperature, then the boiler produces much lower temp water and it is more efficient.

Insulation also matters because if your house has outer insulation then it means that heat transfer from the house to the environment is mostly blocked, but cross-room heat transfer is likely not (through the walls). Therefore it is better to heat the whole house than heating just a couple of rooms because if you do the latter then you'll end up heating the whole house anyway but you're using less surface area (meaning you need higher flow temperatures, meaning less efficiency).

> The reasoning: when you heat up the house, then your boiler needs to produce constant high-temperature water. When you keep the house at the same temperature, then the boiler produces much lower temp water and it is more efficient.

How does your boiler produce heat for your water in your scenario?

> Therefore it is better to heat the whole house than heating just a couple of rooms because if you do the latter then you'll end up heating the whole house anyway but you're using less surface area (meaning you need higher flow temperatures, meaning less efficiency).

Just model the other rooms as very weird wall to the outside.

I think in real life there are more constraints. For example there are people that sleep better at a lower temperature than the daily one (so leaving the thermostat at the same temperature it's a minus for them).

Regarding "what is better" from energy efficiency, I would prefer a system that "check it" because my guess is that it depends a lot based on the individual situation. I mean everybody is going crazy over "IA" but a couple of sensors and a system smart enough to adjust your usage based on your particular situation and preferences (like "eco", etc.) is an exception.

In slightly cooler climates, the answer for sleep is to open windows. This works in much of Europe, even through summer.

But of course, not really feasible in Atlanta or Phoenix. Nighttime temps are too warm.

Open windows in a city often means you are invinting in pollution, both air and noise.

Exactly. Current HVAC systems have extensive filtration; some HVAC systems have HEPA filters.

Opening windows also helps to evacuate inner pollution coming from furnitures, wall paint, parquet and other chemicals...

We are talking about places that need heating here.

In general, you should either run the heater or have your window open. Both at the same time is bad news for your energy bill.

> the theory being that warming up a cold house in the morning costs more energy than maintaining a stable temperature.

That's true if you completely stop heating. However if you lower the temperature by roughly 3.5C when you're not home, you'll be saving energy.

So you can for example program it to be 16C when you're out and 19C when you're in. You don't completely turn off heating indeed.

(UK) my boiler has a control with something like the wake..leave timer (it actually has six settings for a midday period as well) and there is a separate thermostat with a temperature dial. The boiler also has a button that advances it to the next time interval if you want instant on (eg if you come home early to a cold house). I find this combo of controls meets all of my needs, given that I have a fairly repeatable daily schedule.

We've used the Tado system with a central boiler and smart radiator knobs for a few years. It's worked fine and hooks up to Home Assistant and can do the things you describe. I'm sure there are some alternatives.

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