How many (low-temperature) radiators are enough?

[Garald]

So, two narrow, tall radiators at about 500W, each close to one of the two ends of the long inside wall? And another one in the long corridor, since it will be used as library space (and so that it does not count as unheated space)? Does that sound best?

[Garald]

https://www.extremeweatherwatch.com/cities/paris/lowest-temperatures-by-year

[Garald]

Two like these, say? 1508*0.41*2 = 1154 > 916

https://www.leroymerlin.fr/produits/chauffage-plomberie/chauffage-gaz/radiateur-a-eau-chaude/radiateur-a-eau-chaude-acier/radiateur-eau-chaude-vertical-acova-filin-blanc-1508w-h-200-x-l-43-1-cm-82730059.html

Edited September 14, 2022 by Garald

[Garald]

Or just one of these (3252*0.41 = 1333 > 916), though I'm not sure that having just one radiator for such a long space is a good idea.

 

https://www.radiator-outlet.nl/eca-geribbelde-verticale-radiator-200x60-cm-wit-ra.html

 

Or even this one, if we feel like living dangerously (2710*0.41 = 1111 > 916)

 

https://www.radiator-outlet.nl/eca-geribbelde-verticale-radiator-200x50-cm-wit-ra.html

 

Or are two halves really best?

 

[ReedRichards]

If you put in too many radiators or size them for an outside temperature you very rarely encounter then you will need a bigger heat pump.  This will cost more and you may find that it has to cycle on and off a lot of the time when it is milder outside because it cannot modulate down low enough to give you just a little heat continuously.  Conventional wisdom is that this is a bad thing.  My heat pump is sized to give me enough heat at -3.7 C, which in my locale is a temperature achieved 99.6% of the time.   

[Garald]

Well, how far down can a heat pump modulate? (Can't one regulate the radiators themselves, as in any other system?)

 

What is wise? Get exactly what the model instructs me would be enough (on "full") for the kind of chill that happens once every couple of years, as opposed to once a generation? (I am not minded to freeze!) How accurate is the model?

[SteamyTea]

14 hours ago, Garald said:

and then multiply everything by 2

Then we add our birthday, and a little bit more for a laugh.

Oh, engineers, though you said salesmen.

[HughF]

9 hours ago, Garald said:

Well, how far down can a heat pump modulate? (Can't one regulate the radiators themselves, as in any other system?)

 

What is wise? Get exactly what the model instructs me would be enough (on "full") for the kind of chill that happens once every couple of years, as opposed to once a generation? (I am not minded to freeze!) How accurate is the model?

Not as much as a (decent) gas boiler….. there are two schools of thought, size it perfectly to the load and run the fan and compressor at maximum or oversize it and run the fan and compressor slower.

 

I’m going for the latter, buying a 9kW (peak) unit for a 6.7kW modelled heat loss.

[ReedRichards]

10 hours ago, Garald said:

Well, how far down can a heat pump modulate? (Can't one regulate the radiators themselves, as in any other system?)

 

What is wise? Get exactly what the model instructs me would be enough (on "full") for the kind of chill that happens once every couple of years, as opposed to once a generation? (I am not minded to freeze!) How accurate is the model?

 

Different models of heat pump have different ranges of modulation.  I have observed that my 12 kW heat pump seems to be able to modulate down to 2 kW and then upwards in roughly 0.5 kW steps but that was just on one particular day when I was watching it closely.  Of course you can regulate the radiators but that will reduce the demand for heat (although possibly not by as much as you would think) so require greater modulation ability from your heat pump.

 

I have not looked at the heat loss model you are using but you must have to assume an outside temperature to calculate a heat loss.  In principle my heat pump can match the demands of  my house for heat and hot water at -3.7 C with a little bit of headroom.  So if it was -10 C outside I might find that I could only heat my house to 16 C instead of the normal 21 C; in which case I would have to light the stove.  But when it's +10 C outside, my heat pump can provide the necessary heat without having to cycle on and off too much        

[Garald]

It seems reasonable to demand of a heat pump in the Paris area to be able to heat to 20-21C without breaking a sweat when it's -7C outside. For reference, the season-weighted performance of heat pumps there seems to be defined as 0.75*(their performance at 7C) + 0.25*(their performance at -7C). No doubt -7C weather will become rarer and rarer with time, but it's still a temperature that is reached every two years or so, and not always when you expect it.

 

For less than -10C, yes, there's the chimney in the library, but keeping it clean isn't free (and I'm a bit too paranoid to make the chimney in the main bedroom usable, though I could).

 

Here's the information on the heat pump I plan to get (it's the right size for the coop's outhouse, which I have bought for that purpose), but I don't even know what to look for in order to find out how easy it is to regulate. https://www.amzair.eu/wp-content/uploads/dlm_uploads/2015/04/pac-amzair-optimduo-dossier-technique-20211125.pdf

[ReedRichards]

The Technical Dossier doesn't seem to offer any help with regard to ease of operation.  You need to track down the Operating Instructions.

[Garald]

Is this what we seek?

 

https://www.amzair.eu/wp-content/uploads/dlm_uploads/2020/11/pac-amzair-optim-dossier-installation-et-mise-en-service-20211129_5.5_pcooem_l.pdf

[ReedRichards]

No, I don't think so.  That looks like the Installation Instructions; I don't see anything about how to operate the heat pump when it is installed.

[Garald]

I think this must be it:

 

https://www.amzair.eu/wp-content/uploads/dlm_uploads/2020/11/notice-utilisateur-tout-gamme-20210610_5.5.pdf

 

[ReedRichards]

There is an important feature of heat pumps which in the UK goes by the name of Weather Compensation.  It means (if I understand the french correctly) "Les températures d’eau sont calculées en fonction de la température extérieure (intégrée à la machine - loi d’eau)."  When it is warmer outside you don't need as much heat from your radiators.  So the target temperature of the water leaving the heat pump can be reduced, which makes for more economical operation.  The heat pumps in your literature lay claim to this feature but I cannot find how to engage/disengage it or how you would change the compensation curve/line if required.

 

There is another useful feature termed, in the UK, "Load Compensation" which is basically the same as PID ( https://en.wikipedia.org/wiki/PID_controller ).  Again I have not found any documentation on this feature.

 

This lack of documentation is not that unusual.  My installer had to send me a copy of a training manual he had for fuller instructions on my LG heat pump; they were not supplied as standard.