Go to Forum Home › Building Services › Degree-days method
- This topic has 9 replies, 2 voices, and was last updated 10 years, 9 months ago by Tom Foster.
-
AuthorPosts
-
-
1 April 2013 at 8:20 am #31794
Trying to get clear how to establish 'base temp'. From CIBSE Guide A 7th Ed para 2.5:
“Accumulated temperature differences are calculated as the
difference between the prevailing external, dry bulb
temperature and a ‘base temperature’. This is the external
temperature at which, in theory, no artificial heating (or
cooling) is required to maintain an acceptable internal
temperature.”Say an uninhabited building, with no solar gain, only subject to conductive/convective fabric losses/gains (via U-value) and to air-change losses/gains, relative to external dry-bulb air temp. No gain from occupants body heat, lighting/cooking/appliances/hot water tank, no solar gains.
In that case, ignoring thermal lag, stored heat etc, internal air temp will simply follow external air temp. So if I deem the target “acceptable internal temperature” to be say 18C, then 'base temp' – “the external temperature at which … no artificial heating … is required” – must be 18C.
Correct?
-
4 April 2013 at 10:01 am #38868
Bump! Any comments?
-
8 April 2013 at 12:22 pm #38869
Thanks for replying Mark.
In applying the degree-day method, I am hoping to avoid the complicated guestimating that conventionally seems to be immediately involved, to decide on the appropriate 'base temp' for the building – before looking up in the tables you have to know what 'base temp' applies. Whereas I'd prefer an approach that simply makes 'base temp' equal to desired internal temp.
Asking the same question on
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=10336&page=1
got mainly scepticism about my suggestion that gains from occupants' body heat, lighting/cooking/appliances/hot water tank, and solar gains could be accurately estimated as the first contribution to reqd heat input, to which fueled input wd then be added to supply the remainder.They thought a better approach would be to select from some database of comparable buildings plus do some regression analysis, to arrive at a base temp, say 15.5C instead of 18C, which already assumed those incidental gains, so that only fueled input would remain to be added.
To me, the latter approach seems far more of a guestimate, whereas I see little difficulty in quantifying the incidental gains.
Any opinions?
-
24 May 2013 at 6:37 pm #38870
Any opinions?
-
2 June 2013 at 8:47 pm #38871
Tom
It sounds like you should get PHPP and give it a whirl.Mark
-
15 June 2013 at 9:30 pm #38872
I do hope AECB still sees ways of approaching questions, other than PHPP as panacea.
-
25 June 2013 at 8:22 pm #38873
Not expecting you to do all the answering Mark – but where's everyone else gone?
If a simple Q about degree-days can't be asked here, then where?
Note I'm not asking how to calculate gains (which yes PHPP wd be great for) – but want to check the validity of a way to establish degree-days 'base temp'
Don't tell me PHPP holds the answer to that. -
1 July 2013 at 7:28 pm #38874
I've already commented on the basic method. And confimed that you are on the right track.
….erm. There is open software available (auditable i.e. in MS Excel format) that can help you to corroborate that you are using an appropriate calculation methodology. This will help you to ensure that the degree day method that you are employing accords with BS EN standards.
Mark
-
1 July 2013 at 8:42 pm #38875
OK, thanks Mark
-
2 July 2013 at 4:53 pm #38876
Thanks – that's v clear.
… assuming that gains and losses through the fabric were approximately equa
by that you're just confirming, as I said “ignoring thermal lag, stored heat etc”?
-
-
AuthorPosts
- You must be logged in to reply to this topic.