[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [EnergyPlus_Support] ASHRAE 90.1 building envelope compliance methods



Proposed Case:
If your contruction on the proposed design has an insulation layer rating and type (eg. continuous insulation...sometimes even two layers are required) better than the perscribed minimum in the tables, then yes that would show complience. But you still need to model something and then your model construction assembly should have the U-value as determined by the standard (Appx A...and don't forget to de-rate the insulation/framing layer insulation rating). After you have deturmined the U-value, you need to build a construction that will yield this value and keep it as close to the real contruction as possible to retain thermal mass effects.

Baseline Case:
Same process, but if you build the contruction properly using the required Rated insulation R-values from the tables and follow the descriptions of the constructions in Appx A, then you will land almost exactly on the rated assembly u-value listed in the tables. 

Mit freundlichen GrüÃ?en- Sent from my iPhone (excuse the brevity)

i. A.
Jean Marais
b.i.g. bechtold
Tel.   +49 30 6706662-23

On 07.10.2013, at 12:35, <seanking.1970@xxxxxxxxxxx> wrote:

 

Still a bit confused here:


The following is from Users' Manual 2007 SI edition:

For above-grade opaque constructions, the design criteria are expressed in terms of a maximum U-factor or a minimum R-value. If insulation is installed that has the prescribed R-value, then there is no need to demonstrate compliance with the thermal performance (U-factor) of the construction assembly. When using the maximum U-factor criteria, Appendix A of the Standard has defaulted U-factors for most constructions so that you rarely have to calculate a U-factor to show compliance.


If we follow the lines in red shown above, the U-factor used (calculated based on R-value of insulation)) for modelling might still be different with the U-factor read from Table 5.5-1 through 5.5-8.


Any ideas?


Sean



---In EnergyPlus_Support@xxxxxxxxxxxxxxx, <energyplus_support@xxxxxxxxxxxxxxx> wrote:

The thing not to confuse is that the requirement to the insulation layers of the construction assembly is not the same as the total assembly U-value. Also, like Sean said, if you hand calculate the U-value of a construction as put forward in Appx. A, you will find that they closely match with those in the Tables (there are some rounding errors, especially from I-P to SI units. Just don't compare the R-values required of the insulation to the U-values of the entire assembly and expect to get the same values.



---In EnergyPlus_Support@xxxxxxxxxxxxxxx, <energyplus_support@xxxxxxxxxxxxxxx> wrote:

If you use Appendix A in 90.1, you will find that the required R-values come very close to the required U-factor as long as you use the construction assemblies as described in the appendix. If your construction assemblies are significantly different than those specified in Appendix A, then the U-factor path should be used (for both baseline and proposed).


Look to the 90.1 Users' Manual for more guidance.


Rahul





---In EnergyPlus_Support@xxxxxxxxxxxxxxx, <energyplus_support@xxxxxxxxxxxxxxx> wrote:

The consensus for modelling purposes at least is that the U-value of the assembly is to be held for the baseline case. The R-value of the insulation layer is not nessesary, although constructions can be made to apply to both. Note the R-values of insulation layers are "rated" values which sometimes need to be derated in accordance with appx A (eg. Steel-framing/insulation layer).

A note to some other recent posts regarding ASHRAE rated assembly U-Values: e+ calculates these according to the ASHRAE 90.1 standard for the summary reports.

Mit freundlichen GrüÃ?en- Sent from my iPhone (excuse the brevity)

i. A.
Jean Marais
b.i.g. bechtold
Tel.   +49 30 6706662-23

On 04.10.2013, at 12:58, <seanking.1970@...> wrote:

 

Dearl all,


In ASHRAE Standard 90.1 2007 SI Edition, Page.18, it states:


5.5.3 Opaque Areas. For all opaque surfaces except doors, compliance shall be demonstrated by one of the following two methods:

1. Minimum rated R-values of insulation for the thermal resistance of the added insulation in framing cavities and continuous insulation only. Specifications listed in Normative Appendix A for each class of construction shall be used to determine compliance.

2. Maximum U-factor, C-factor, or F-factor for the entire assembly. The values for typical construction assemblies listed in Normative Appendix A shall be used to determine compliance.


My question is simple but very confused to me:

While modelling baseline buildings, there must be different U-factors between using these two options (using certain R-value from column next to U-factor column will certainly not generate the same U-factor shown in that column). Therefore EnergyPlus will generate different outputs on thermal performance (I am quite sure E+ works out heat transfer through building element using its U-factor). 

So the question is: How do we know which method we should use in the model? I suppose everyone might prefer a bigger U-factor (when creating a baseline building) for whichever method being used.

Is my understanding right? I look forward to any advisable comments.

Sean

Reply via web post Reply to sender Reply to group Start a New Topic Messages in this topic (6)
|**|begin eg


__._,_.___


Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx

The primary EnergyPlus web site is found at:
http://www.energyplus.gov

The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/

Attachments are currently allowed but be mindful that not everyone has a high speed connection.  Limit attachments to small files.

EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.



Your email settings: Individual Email|Traditional
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch to Fully Featured
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe

__,_._,___