Combining an air-water heat pump and solar thermal

[Garald]

Sorry, winter *morning*. 15 W m^{-2} is slightly optimistic but not wrong, at least not on a sunny day. See http://susdesign.com/windowheatgain/index.php  Bit counterintuitive, in that the peaks for March and October are higher than those at other times - why is that?

 

Bit funny that 15 W/m^2 should give very little rise in temperature, given that that's not what it happens in the summer, and, if the app is right, one doesn't get more than 10 W m^{-2} then. Latitude 49 N, orientation SES.

 

 

[Garald]

Let me see. Consider a fairly sunny winter morning  in late December, with sunlight falling head-on to bookcases directly in front of them (this is essentially what the simulation shows), transmitting about 10 W/m^2 to the bookcases. 

 

 

It's actually hard to choose whom to believe about the volumetric specific heat of different kinds of wood - if you believe that, as is often stated online (e.g. https://tinyurl.com/4hmedzr9), the specific heat of pine is 2300J/kg C (at which humidity?) then IKEA pine would have a volumetric specific heat (heat capacity) of 0.92*10^6 J/m^23C - yet, according to https://tinyurl.com/yc72tjhz  (which looks like a serious source), even oak barely achieves 0.85*10^6 J/m^2 C at 10% humidity.

 

Well, let us say that we have empty bookcases with backpanels that are made of 2cm of solid wood with volumetric specific heat 0.8*10^6 J/m^3 C. That gives us 16kJ/C per square meter of surface. Since 10 W/m^2 means 36 kJ/hour m^2,

we see that the backpanels are getting 2 C warmer every hour, for, say, 2 hours.

 

Surely that's good - that means that the bookshelves are absorbing not so very little heat without breaking a sweat. What difference will they make on the room temperature, or on the energy radiated in the course of the day to someone directly in front of them? I don't know.

 

What is also clear is that a flimsy backpanel would not absorb all that heat (its temperature would change significantly and quickly, and then its heat-absorption properties would change). Of course there are also books, but they don't cover the backpanel entirely.

 

The moral, I guess, is that it is not actually stupid of thinking of having bookshelves with solid-wood back panels, if they are going to have sun shining directly on them on sunny but cold winter mornings, and you'd like the heat back later in the day.

Putting 3mm cork sheets on the back of those panels may be overkill (since the temperature of the backpanel will have risen by at most 4C or so) or not - I do not know.

 

Or am I interpreting this wrongly?

[Garald]

And on books, right, I would never put them in a basement. Direct sunlight indoors is not that bad - at most, the spines will get discolored over the years. I don't recall that actually happening to me  - though come to think of it, my Springer volumes do seem to be of many different shades of yellow now... At any rate, since I've barely noticed, it's not a problem I would think important.

[Garald]

Oh. I was assuming 0 light reflectance. 

 

So, the conclusion should really be: it is not necessarily stupid of thinking of bookshelves with solid-wood back panels that are relatively dark (varnished, painted, it may not matter)?

[JohnMo]

I will bow out, way to much effort being spent discussing the thermal properties of books and book shelves.  No idea what that has to do ASHP or solar thermal.

 

 

 

 

 

 

[SteamyTea]

8 hours ago, Garald said:

See http://susdesign.com/windowheatgain/index.php  Bit counterintuitive, in that the peaks for March and October are higher than those at other times - why is that?

Only had a quick look, but the units are showing kWh.m^-2.  Is that for the whole month?

So taking January, at noon, 13 kWh.m^-2

Divide by 31 (days in month) and that comes out as a mean of 0.42 kWh.m^-2.

This seems a bit high, but may be correct for a clear sky when the direct beam is measured.

[Garald]

4 hours ago, JohnMo said:

I will bow out, way to much effort being spent discussing the thermal properties of books and book shelves.  No idea what that has to do ASHP or solar thermal.

 

 

 

 

 

 

Well, I said it was veering off-topic, but it *is* solar thermal, after a fashion, with a wooden tank full of books instead of water, and serving both as solar panel and as a radiator.

 

[SteamyTea]

5 minutes ago, Garald said:

but it *is* solar thermal, after a fashion

Passive solar heating.

The one thing that has always crosses my mind when thinking about it, is, if it worked, we would all be using it.

[Iceverge]

 

 

 

ST isn't at the races anymore unless you have only a tiny area of roof to work with. 

[Garald]

3 hours ago, SteamyTea said:

Passive solar heating.

The one thing that has always crosses my mind when thinking about it, is, if it worked, we would all be using it.

 

Well, but it is becoming the thing - Passivhaus and so forth; the question is whether get any of that to any perceptible extent when renovating an old building.

[SteamyTea]

38 minutes ago, Garald said:

question is whether get any of that to any perceptible extent when renovating an old building.

Realistically only by building a new house inside the old one.

Biggest problems, in old houses, are low insulation, thermal bridging and dreadful ventilation control.

Apart from that, they are quite good.

[Garald]

Right, I'm going to be working on all three. Or rather, I'll be helping the architect a bit on the first two, and watching her work on the last one; she's a ventilation expert. 

 

I'm getting the keys in ten days' time, and then we get started with a thermal camera.

[SteamyTea]

5 hours ago, Garald said:

I'm getting the keys in ten days' time, and then we get started with a thermal camera

Post up the pictures, we all like thermal images.

[Garald]

Got the keys on Tuesday. The morning of the purchase, I set the heater on low, and set the thermostat to 26C. When I went back in the evening, the house was properly overheated, in spite of its poor insulation, and the heater showed 40C as the water temperature. (Of course it may have gone higher; the heaters felt somewhat warmer than 40C, though not by that much - I could put my hand on them for an arbitrarily long time.) It wasn't a cold day - just a rainy spring day, with sun for a couple of hours in the afternoon. 

 

The previous owners told me that they never put the heater at a level beyond medium (which seems to correspond to 60+epsilon), and that seems to have been quite enough even in winter, even though the insulation is quite bad.

 

All in all, I suppose that's evidence that a low-to-medium temperature will suffice, right? The radiators are largeish (except for those in the main library, which also has southern exposure and a chimney).

 

I had a long talk with the architect on Wednesday while she checked every wall with a thermometer. We'll probably choose 15-20cm of alveolar insulation (synthetic), except for a wall with humidity issues, where we plan on using hemp-based insulation, and a few places where we don't have much width to work with and we'll use cork (or something as high-performing as cork). Sounds reasonable?

 

We haven't got thermal images yet - I'm trying to hire a certified technician to do that, so that I can get the subsidies you are supposed to get in France when you undertake major energy-efficiency renovations.

[joth]

13 minutes ago, Garald said:

It wasn't a cold day - just a rainy spring day, with sun for a couple of hours in the afternoon. 

Did you record the outside temperature at all? Otherwise any experiments are quite meaningless.

 

In my experience (in the UK) using a thermal imaging camera any time other than winter (sub 10°C outside, ideally sub 5) won't yield much useful information at all. Will be interested to see what you can achieve in mid summer.

 

 

[Garald]

Weather Underground states the temperature at a nearby weather station to have been 13C when we got started (8:30am) and about the same when I dropped by, but it peaked at 19C in the afternoon. Really not great, but we did what we could - we'd even programmed things in advance so that we would get a spot of cool weather. The first full week in June will be about the same - that will be our last chance to hire someone to use a thermal imaging camera and not get garbage, I take.

 

Before we tested the walls with a laser thermometer (Wednesday morning) I took care to heat the entire house up to 30C. We did get very different results on different walls. All recent windows were surprisingly good (they were about 29C) but the walls were all over the map, from 20C to 30C, if I remember correctly. (25C seemed typical; only a couple of nasty spots got 20C).

[SteamyTea]

3 minutes ago, Garald said:

Before we tested the walls with a laser thermometer (Wednesday morning) I took care to heat the entire house up to 30C.

Better off doing it a few hours after sunset, then surface wall heating from solar gain is not distorting the readings.

[Garald]

I'll probably have to do that myself then. I guess all laser thermometers are born equal?

[joth]

11 hours ago, Garald said:

We haven't got thermal images yet - I'm trying to hire a certified technician to do that, so that I can get the subsidies you are supposed to get in France when you undertake major energy-efficiency renovations

Just to understand, thermal camera imaging (before and after?) is a mandatory part of the process to get the subsidy? (At first I thought you were saying you can't get money off the imaging work unless it is certified, not that it's mandatory)

I'm interested in how this whole process works. (I doubt it's documented in English at all.🤣)

 

So the idea is to overheat the house as hot as possible and then measure the temperature grade visible outside, even if it's >20°C outside temperature in the shade?

Certainly sounds like a job best done at night time

 

Thanks 

 

Edited May 27, 2022 by joth

[SteamyTea]

Just now, joth said:

Certainly sounds like a job best done at night time

The assessor can do it on the way home from his mistress.

[joth]

9 hours ago, Garald said:

I'll probably have to do that myself then. I guess all laser thermometers are born equal?

 

Laser thermometer is probably the way to go, but if you're interested in getting more information then I found a thermal camera that plugs into a smartphone to be pretty handy. 

 

 

 

[scottishjohn]

Combining an air-water heat pump and solar thermal

 this is very possible as it was what I did a long time ago   mylimitations was lack of computers and knowledge for ideal control system -

I,m sure that is all doable easily now assuming modern insulation valves

-but to get best from any solar thermal you need large storage volume - 30c+ from solar panel will be availbe virtually every day of the year -- if underfloor and insulated well it will run that

 the calculations that I came up with -- do your own 

was 10000litre storage for all your heating year round assuming 40-50c  tank temp and plenty of extra heat will go to DWH tank  

you are not trying to get very high temps --just a large volume -you will get high temps with good panels to do DHW  as well --I could send my 300litre tank from 17c in morning(as it run  underfloor overnight ) to boiling by 13.00 hours on a good sunny day ,-40 thermmax unregulated tubes

yes you could use it on most days reasonable  days for HW -- but that would mean more complications in valving -so it always heats HW tank first then when that is full or temp is not high enough it reverts to heating your main lower temp heating storage tank 

I am contemplating the system for my house and maybe less tank size +PV panels to eun elec heater  and maybe 1000litre tank 

 tank would have at bottom  solar coil then underfloor coil in middle and DHW at top 

 

not sure with price of panels +tank  whether it would be any cheaper than a ASHP

still plotting

 

 

Edited June 5, 2022 by scottishjohn

[Roger440]

11 hours ago, scottishjohn said:

Combining an air-water heat pump and solar thermal

 this is very possible as it was what I did a long time ago   mylimitations was lack of computers and knowledge for ideal control system -

I,m sure that is all doable easily now assuming modern insulation valves

-but to get best from any solar thermal you need large storage volume - 30c+ from solar panel will be availbe virtually every day of the year -- if underfloor and insulated well it will run that

 the calculations that I came up with -- do your own 

was 10000litre storage for all your heating year round assuming 40-50c  tank temp and plenty of extra heat will go to DWH tank  

you are not trying to get very high temps --just a large volume -you will get high temps with good panels to do DHW  as well --I could send my 300litre tank from 17c in morning(as it run  underfloor overnight ) to boiling by 13.00 hours on a good sunny day ,-40 thermmax unregulated tubes

yes you could use it on most days reasonable  days for HW -- but that would mean more complications in valving -so it always heats HW tank first then when that is full or temp is not high enough it reverts to heating your main lower temp heating storage tank 

I am contemplating the system for my house and maybe less tank size +PV panels to eun elec heater  and maybe 1000litre tank 

 tank would have at bottom  solar coil then underfloor coil in middle and DHW at top 

 

not sure with price of panels +tank  whether it would be any cheaper than a ASHP

still plotting

 

 

 

Be sure to keep us updated.

 

The appeal of ST is that its DIY-able more easily. And hence much cheaper. The actual level of efficency is rather  unimportant if it gets the job done in a cost effectve manner. Computers and software are something i reallk dont want involved if at all possible. Partly because i struggle with them, and partly because they are invariably more unreliable than what they are managing, and always unsupported 5 mins after you bought them.

 

Of course, you do need space for large tanks.

[scottishjohn]

2 hours ago, Roger440 said:

Computers and software are something i reallk dont want involved if at all possible. Partly because i struggle with them, and partly because they are invariably more unreliable than what they are managing, and always unsupported 5 mins after you bought them.

you could do it in an analologue fashion  with multiple temp stats -if panel above 50c then divert to DHW and when bbelow go to unbderfloor and when dhw reachs max required  temp another one to divert it to underfloor tank,I,m sure there will be a controller out there by now that can do that -was not one when i did my system 20 years ago  in last house 

[bontwoody]

Im actually thinking of doing the same. The house already has 3kW of PV panels which take up virtually all of the good roofspace. My plan is to use a smaller area of SW facing for for 30 evacuated tubes. Because of the higher efficiency of the ST, Im getting a lot of bang per square metre. This should produce most of my DHW for the year with the heatpump propping it up in the winter. Another issue in the UK is the escalating prices of PV and getting an installer to fit them at the moment. I plan to DIY install the ST and connect it to a twin coil cylinder.