Several Questions

Carlos · Posts: 25

Hi DB.

I have recently started simulating in DB (I did some in E+). Since this copy of DB is registered, I'll be posting questions daily perharps Wink

I readed all the manual (1.2), but it's quite uncomplete, as a suggest, please, take a little more at it (maybe not as much as the 50 hundred pages E+ has, but more, yes). So,

1) Wall thickness is specified from the project's start, but nothing is mentioned about floor and roof, ¿are they considered as bidimensional objects with no thickness? In the visualization of the house Im'm simulating it appears so, but oppening an example file (Trombe Wall) a thick roof is seen. The roof height is from the upper side of the floor to the lower side of the roof?

2) I found no reference on how to set a paint coating on the outter surfaces of the building. This is a very important issue in the climate i'm simulating (very hot). So, how do i do it?

3) I want to draw walls separated from the Block, not belonging to any zone, just a wall (it doesn't affects the zone's temperature directly, but blocks solar radiation and wind). Also want to put overhangs but wherever I want to put them, not unavoidably at windows, how do i draw them?

4) For the 'montlhy temperatures' at site level, I used the Taverage that are produced by the Slab Program in Energyplus. When running the simulation, find that there is an unbeliveable flux of heat to the ground. I'm modelling an economic dwelling in a zone temperature is most of the day over 30ºC, but te results shows the zone near to a comfort zone because the floor loses up to 2kW. Maybe it could make sense in humid earth, but this climate is very hot and dry, the earth is not a good conductor of heat. What's happening? Is the program really taking into account a poor heat transmission (even when ground temperatures are as low as 20ºC)?

Regards,

Carlos

AJ Lester · Posts: 71 Location: Auckland

Welcome to the DB forum Carlos!

Some replies to your questions, although I can only offer advice that might help, not always definitive answers!

1) In general I think the answer is that the construction is treated in the same way as the walls: thin in representation and volume calculations but thick when the thermal mass etc is worked out. I believe this will partly depend on how you have set up your floor/slab/ceiling representation parameters. To check or change these parameters:

Go to Model Options>Data Tab.

Under Construction and Glazing Data heading you should see a heading marked Zone volume calculations. This heading allows you to select whether or not floor constructions will be subtracted from zone volume. Perhaps setting the height of the walls to be high enough to incorporate your internal floor/ceiling construction and selecting the option to subtract the volume of the internal floor from the zone will make it work?

2)I would suggest that if you know the emissivities reflectances etc. of the paint you intend to use that you could make a copy of the external wall construction you intend using and change its outside emissivities, reflectances etc. to match your paint. (this is just an intuitive answer, there may be a better solution to your problems).

3)Use component blocks. These are entirely designed to act as exterior shading devices without having any thermal zones to simulate. To do this, create a new block, but under block type, select component block, not building block. You can then draw a block of any thickness and size that will shade, useful for external fixed shading devices as well as nearby buildings etc.

4)I take it that you have set up your monthly temperatures at the building level under Location>Site Details>Ground>Monthly Temperatures. Have you also checked on the same tab which ground construction exists for your building? The Cultivated Clay soil that DB defaults to has a fairly high U-Value which may not be suitable for the hard, dry soil you speak of. Finally, although you have almost certainly done this, just in case you haven't, you will need to confirm that your ground floor object is appropriate for the type of construction you are modelling.

I hope some of this might be of help to you.

All the best with your modelling!

Andrew Lester

AJ Lester · Posts: 71 Location: Auckland

Hello again Carlos,

Further to my earlier comments, please take a look at this post on the forum as it contains some very useful feedback from a very capable and knowledgable DB user. It relates to your Q1 and the way that floor/ceilings are dealt with in DesignBuilder.
http://www.designbuilder.co.uk/component/option,com_forum/Itemid,25/page,viewtopic/t,1134/

Again, good luck!

Andrew

Carlos · Posts: 25

Hi.

I tryed finding solar and visible absortances and emissivity for paints, but coulnd't. Only found that generally, emissivity is 0.9 and some solar absortivities. I'm using visible absortance as equal of solar, good aproximation?

The problem came when when adding a material. I added 2 paint materials to the folder "Other". Then i tryed to used them in a construction, but... there was no material in the folder. I searched all te folders in materials and there was nothing. I then created one again and DB didn't let me use the same name I former used because "the file is in use". I used a secondary name, went to constructions and again showed me the folder empty. Came back to materials and it was where I left, in folder 'Other'. I reestarted DB, went to materials and... again, folder 'Other' is empty. What's Hapenning?¡¡??

Also, when running the Design Capacity, DB doesn't notify me of any error, and shows outputs, except that for Total Design Requirement (kW).¿?¿?

Carlos

AJ Lester · Posts: 71 Location: Auckland

Hi Carlos,

I think you'll find that the visible absorptance of the paint you select will be more or less solely defined by the colour of the paint you choose. From memory, white reflects about 96% of all visible light (i.e. visible absorptance of about 4%) and conversely black reflects about 4% of all visible light (i.e. visible absorptance of about 96%). I found some generic paint data that had similar emissivities, all around about 0.9, so this seems to be a reasonable value. Just be aware that if you are using, for example, an aluminium-based paint these frequently have lower emissivities as do some high-gloss laquers.

There are two possible problems I can maybe see with your materials issue:

Firstly, it is important to make sure not to confuse the "materials" with "constructions". Materials are made and are then used as parts of a construction. You will need to add materials to the database, then use these materials in a construction.

Alternately, if this is not the issue, what you may have to do to see those other materials that you have created is the following (taken from an earlier response to a similar issue).

Carlos · Posts: 25

Hi Andrew,

I'm using common paint, so i'm not using aluminum-based finishings.

I have clear the difference between Materials and Constructions. I created some materials, but when trying to create a construction, the material I created earlier don't appear. I tryed then to activate Show Other Regions Data. It worked... partially:

-When I have none project open, the materials now do appear in the folder I created them and I can create a Construction based on them.
-When I open a project, the materials I created, again don't appear in none folder. The constructions I created don't appear either. I already verified when I have a project open, the option Show Other Regions Data is still activated.

It now seems a dream, but I remember in the first days I created some constructions outside any project and could use them in a project by something like 'calling all data', but I don't remember how I did. How do I do it now? I'm in a kind of limbo between the DesignBuilder with no open project and the DesignBuilder with open project. Need to merge them, I don't think it was te best idea to split the data, it carries more troubles than solutions.

About 'the third question', I forgot to upload the file. Now I do, it's 'Prototipo 1-Base'. The problem is that I run the design day simulations (both, Heatign and Cooling), but the kW needed are 0,0 always.

Thanks for your time,

Carlos

Laurent_Support · Posts: 292 Location: Vincennes

Hello,

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