Measuring How A Room Behaves Thermally
By measuring the thermal performance of a room over an extended period, but especially through the heating season, I should get an idea of any further work that could be done in that room or elsewhere in the house (for example in reducing unwanted air infiltration) to further improve performance. We're never going to hit Passivhaus levels of insulation or air-tightness, but this should give us a clue where real remaining returns may be lurking, getting us closer to the goal of no space heating needed at all, and thus minimised bills and carbon footprint.
Nick Taylor very kindly donated/lent me a number of bits of kit 2011/10/09, including four iButton temperature sensors (DS1921G-F5 "Thermochron" devices and USB reader, each capable of recording 2048 data points at regular intervals), with which I hope to monitor temperature in and around the room over an extended period (a year or more if possible), at sampling intervals of ~1h reflecting the time scales of forced temperature changes, eg from putting rads on before bed.
I expect to use a finer granularity to start with, then when I get bored of crawing around in the loft to download data, etc, drop to a coarser measurement interval.
| Number | Device ID | Target Location |
|---|---|---|
| 1 | A70000002B776221 | In floor void under room. |
| 2 | A70000002B82C321 | In room ~mid-height (~1m up). |
| 3 | A70000002B9A4F21 | Just above ceiling plasterboard in loft (under most of the loft insulation). |
| 4 | A70000002BAE8D21 | Above loft insulation. |
Mission 1
For the start of this 'mission' beginning early afternoon 2011/10/09, expected to run until about the start of November, I have reset all four iButtons to take samples every 30 minutes (in °C) (so should last just over 42 days before filling up), no roll-over allowed, synced to my laptop's time and with low- and high- temperature alarms at 0/40. Initially I am going to let them sit together to calibrate against one another.
I will deploy the ones that I can (into the loft) later the same day, but the others may have to wait until work on the room is completed which may take several more days.
Initial samples when all four were left stacked together on my desk at an ambient temperature of ~19.6°C, in .csv files: 1, 2, 3, 4. All are showing in the middle samples 19.5°C or 20°C which indicates an accuracy/precision of 0.5°C and all reasonably close. The timestamps in the .csv files indicate BST, ie local time, rather than UTC, so I may have to be careful with 'missions' that cross BST/GMT boundaries.
By 2011/10/09 16:40BST (15:40UTC) all four buttons had been deployed, with the following caveats:
- Pinned (in small plastic bag) to joist in floor void quite close to rad pipes and exterior wall (and possibly in a draught) so will probably show wild temperature swings. May have to be moved during remaining insulation/redecoration works on room.
- Pinned (in small plastic bag) behind door out of the way for now. May have to be moved during remaining insulation/redecoration works on room.
- In small plastic bag. Actually next to loft hatch above landing for ease of access, not actually above room but only a few inches at most from its perimeter.
- As stated, pinned to rafter hanging approximately above centre of room.
After about 24 hours I took current samples from under-floor and in-room (the room has had the windows wide open all day and night to dry the plaster):
which shows the floor void to be a little better sheltered than I'd feared (the temperature dropped much less overnight than in the room). See .png graph.
2011/10/15 17:00 BST: with all the insulation work done (including the aerogel-filled window reveals today) I will be closing the windows for a few days, and will keep the doors shut at night, to get an indication of the thermal performance of the rooms unheated with forecast daytime max temperature ~16°C and night min ~6°C.
2011/10/16 10:30 BST: with the room windows closed, external temperatures dropping, and no heating on, the temperature under the floor can be seen to be dropping much more at night, probably due to the draught/infiltration that can be felt by hand from outside!
See .png graph.
2011/10/19 and 2011/10/20: the room was being primed and painted, so windows were open during the day and at night.
2011/10/21: radiators being fitted (etc) in late afternoon/evening (and air-infiltration under the floor greatly reduced with squirty foam), so windows open and iButton 1 displaced to behind the door for the duration. After all done, windows closed and another set of readings captured:
See .png graph.
(2011/10/23: in early afternoon briefly opened window to dissipate some paint fumes and let in some sunlight and again briefly a couple of times more, but room otherwise remaining shut/curtained from morning of 22nd for about 3 days.)
2011/10/25: now with all four sensors graphed, the dramatic swings in the loft temperature (4/purple) can be clearly seen, while over the last 3 days the underfloor (1/red) is much more stable suggesting that the air infiltration probably has been reduced.
See .png graph.2011/10/30: with the room now occupied for a few days (and heating still not on) temperatures seem to be drifting slowly upwards. (Only sensors 1 and 2 updated this time. Sensor 2 has moved to the bookcase.) Note that the .csv files a given in local time, so there's a 'repeat' hour starting at 1am on the 30th as the clocks went back. (A spike up to 20°C on sensor 1 and 21°C on sensor 2 can be seen at 12:12 as the readings were taken on the laptop; glitches to be expected.)
See .png graph.
2011/11/04: central heating went on briefly a little before 6pm today. A fairly sharp rise by 1.5°C to 19°C at 18:42 can be seen for sensor 1 probably as expected due to its proximity to the CH pipe run; the room itself only got to 19.5°C.
2011/11/06: external temperatures have been between about 14°C; day and 11°C night. (Only sensors 1 and 2 updated this time.) There is just over a fortnight's life left of this mission: I still expect to see heating on before its end.
See .png graph.
2011/11/07: after sudden panic that I did not know actually depth of loft insulation (which I then measured as 240mm--300mm approximately), I took the opportunity to take readings from the two sensors in the loft (and move the 'above ceiling' sensor 3 more directly over the room. Did not want to disturb the carpet again so did not read sensor 1.
See .png graph.
2011/11/14: after death of W7 laptop (again) spent much of the day trying to get some sorts of reader (preferably Java) working on Linux (SheevaPlug) or OS X, so readings for sensor 2 reflect that of my desk rather than Morgan's room! I am managing to cobble something together using owfs directly on the SheevaPlug, having failed to get anything Java-y to work there on the Mac. The initial data set showed a bizarre 31-day offset, ie one month out.
- in 2 (.dat) *nx timestamp and degrees C
On my system command to mount owfs is:
/opt/owfs/bin/owfs --allow_other -C -u -m /owfsmnt/
For install, background, etc, see for example:
- owfs (One Wire FileSystem) on SourceForge.
- iButton/1-Wire in the Ubuntu forums.
- Installing 1-wire USB adapter DS9490R on Ubuntu 9.04 noting in particular the other packages to apt--get first: automake autoconf autotools-dev gcc g++ libtool libusb-dev fuse-utils libfuse-dev swig python2.4-dev tcl8.4-dev php5-dev.
- script cobbled together to extract data from owfs.
2011/11/18: taking samples and ending mission 1 shortly after noon today, using owfs:
- under 1 (.dat) *nx timestamp and degrees C
- in 2 (.dat) *nx timestamp and degrees C
- ceiling 3 (.dat) *nx timestamp and degrees C
- loft 4 (.dat) *nx timestamp and degrees C
Mission 2
I've started mission 2, with buttons in the same places, with a more (synchronised) sampling of once per hour on the hour starting at approximately 2011/11/18 15:00 GMT/UTC.
The owfs reader still sees a time 1 month out from the Windows 7 reader. Grrr.
2011/11/20: a quick sample of the in-room sensor (2) shows that temperature was never below about 18°C overnight even though outside was about 4°C at 07:30-ish. handily preceded by a little late afternoon sunshine ie local greenhouse effect!
- in 2 (.dat) *nx timestamp and degrees C
2011/11/24: another quick sample:
- in 2 (.dat) *nx timestamp and degrees C
2011/12/11: a full sample set, c/o owfs:
- under 1 (.dat) *nx timestamp and degrees C
- in 2 (.dat) *nx timestamp and degrees C
- ceiling 3 (.dat) *nx timestamp and degrees C
- loft 4 (.dat) *nx timestamp and degrees C
2011/12/23: a full sample set, c/o owfs:
- under 1 (.dat) *nx timestamp and degrees C
- in 2 (.dat) *nx timestamp and degrees C
- ceiling 3 (.dat) *nx timestamp and degrees C
- loft 4 (.dat) *nx timestamp and degrees C
2011/12/27: just the in-room sensor (2) shows that temperatures have been rock solid over the last couple of days while the house has been empty (13.5°C) and the MHVR off:
- in 2 (.dat) *nx timestamp and degrees C
2012/01/06: a full sample set, c/o owfs:
- under 1 (.dat) *nx timestamp and degrees C
- in 2 (.dat) *nx timestamp and degrees C
- ceiling 3 (.dat) *nx timestamp and degrees C
- loft 4 (.dat) *nx timestamp and degrees C