Building Time Lag-Thermal Modelling 1

[friartuck]

Has anyone got any decent info on thermal lag and the effects on the buildings heating/cooling system.

I am working on a job where the client wants to do some 'new' things i.e. avoid cooling or at least reduce it by using the buildings natuaral ability to absorb heat into the structure.

I understand that concrete has a 'admittance factor' which is the ability of the fabric to absorb heat (rather than let it pass through in an equilibrium sort of way)

I need to know how for instance making the floor 300mm concrete as against say 100mm concrete will affect the building and the heating/cooling systems.

I went to see a building in Germany with an 'eco' design and this had 300mm concrete on top of 100mm insulation. There was external solar shading, etc.etc and natural ventilation.

I know that building constructed in the 1800's were relativeley thermally heavyweight and subsequently much cooler than todays modern lightweight buildings.

Anyone got any experience in this department---or is there a good 'read'anywhere?




Friar Tuck of Sherwood

 

[GMcD]

Here's a link to a good website with a lot of other stuff on it:

http://www.squ1.com/index.php?http://www.squ1.com/passive/passive.html

-play with the thermal mass time-lag diagram there.

I've been designing thermal mass buildings for a while now, and have it down to some pretty simple rules of thumbs. The key is to concentrate on reducing heating and cooling loads by a high performance envelope first, especially the glass - eliminate solar heat gains and have high thermal performance to reduce/eliminate the perimeter versus interior thermal loads differential. There is a fine balance to be made when controlling solar heat gain- you want to reduce it so the cooling requirements are low, but you also want to have "some" amount of it for passive solar heating, depending on the specific climate zone you are designing the building for.

Here are some other links to surf:

http://www.empa.ch/plugin/template/empa/*/5383/---/l=1

http://www.termodeck.com/index.html

http://www.bigwalls.net/johnm/thermalmass/Thermal.ppt

http://www.sustainable-energy.vic.g... design/Energy efficient design/materials.asp

- click on the thermal mass fact sheet in the blurb there.

greenbuildings.santa-monica.org/pdf/en6.pdf

Do a google search on keywords like "building thermal mass design" and the like and see what else you get. My own experience is for designing radiant slab heating/cooling systems along the lines of the Swiss Batiso Buildings and similar to the stuff that Transsolar has been doing in Germany.

 

[friartuck]

wow

thanks

looks like some really good bedtime reading

thanks again GMcD

Friar Tuck of Sherwood

 

[GMcD]

You're welcome. Play around in that

http://www.squ1.com

website- the link I posted above was supposed to take you to the Thermal Mass calculator link - but when I tried it it just takes you to the opening page for the passive design section. Look on the left side of the Squ1 Page there, and find the link that says "Efficient Design", then to "Thermal Analysis", then to "Thermal Mass" and there are a couple of graphic "toys" to play with to simulate the thermal time lag of different building assemblies.

HVAC engineers need to know how the building envelope performs - building physics.

 

[IRstuff]

But, I think that this is already accounted for by the A/C system anyway.

The A/C won't kick in until a certain temperature is reached, which is where the building lagged it to in the first place.

TTFN

 

[GMcD]

IRStuff: yeah, but better passive building design reduces and eliminates the need to techno-AC solutions. If the building envelope is designed properly, you can virtually eliminate a large amount of energy and infrastructure to heat and cool a building for human comfort. The lowest life cycle cost component of a high performance HVAC and lighting system is the windows and the solar control thereof. A thermal mass system allows the cooling loads to be offset to later in the day/evening when people leave the building, and you can either use cool night air to "re-cool" the mass, or hydronic radiant systems to re-cool the internal mass, or, if the diurnal temperature swings are high, do nothing, and the natural cooling overnight will cool the mass off and it will stay cool during the hot daytime. Typical middle east architecture. Cliff dwellings and the Anastazi, old churches all over, etc.

 

[imok2]

This seems to be in your neck of the woods

Bennetts Associates £22m Wessex Water headquarters is so environmentally friendly that its better than the BRE's idea of as good as it gets! The building itself looks to have achieved an energy rating one third of that of an air conditioned city office block of the same size. The concrete mass of the structure serves as a heatsink, and the ventilation relies on opening high level windows. Though the cafeteria, boardrooms and mechanical control centre do have mechanical air conditioning, everything else is worked by nature
Building. 20 October