ASHRAE Journal - February 2011 - 62

solar Nzeb project	

photo 1 (left):	Installation	of	the	insulated	concrete	form	(ICF)	foundation	blocks	around	Equinox	House	perimeter.	Note	the	plastic	 web	that	both	holds	the	Styrofoam	walls	together	and	supports	the	rebar.	photo 2 (right):	ICF	foundation	wall	prior	to	pouring	 concrete.	Note	that	the	concrete	footer	below	the	ICF	wall	is	close	to	the	original	grade	of	the	surrounding	ground.

Ground Heat transfer
W
by ty Newell, Member	ASHRAE; and ben Newell, Associate	Member	ASHRAE

ith	few	exceptions,	visitors	to	Equinox	House	ask	how	much	

insulation	is	below	the	concrete	slab	floor.	There	is	no	insula-

tion	below	the	floor.	Ground	heat	transfer	in	buildings	is	an	important	

factor,	especially	in	regard	to	superefficient	buildings.	But	it’s	difficult	 to	analyze,	model,	and	predict.	In	designing	Equinox	House,	we	looked	 at	the	foundation	wall	and	underslab	ground	heat	transfer	in	relation	 to	the	house	loads	and	energy	cost	to	decide	whether	to	use	insulation.
The coupling between a building and the ground is difficult to define due to the transient, multidimensional analyses required along with a general lack of property information for soils in a specific location. For our design assessment, we constructed a finite volume heat transfer model. The simulation is a three-dimensional, transient model that solves an implicit form of the conduction equation for the ground and foundation wall regions. We define a region that extends 30 m (100 ft) horizontally from the building perimeter and 5 m (16 ft) below the floor to a level where we define a constant ground temperature of 10°C (50°F). Computational cells are 1 m by 1 m (39 in. by 39 in.) in horizontal dimensions by 99 mm in depth (3.9 in.). Approximately three years of iterations are required to reach a cyclical thermal steady state.

Soil properties are always a problem. What type of soil? How wet is the soil? The structure’s floor is quite complicated as well. Underneath the slab are thickened concrete regions under the internal bearing walls, some internal piers that tie into the footer but leave the insulated concrete form (ICF) wall intact, some sand in the plumbing drain trenches, fill from who knows where, and crushed rock. Under the house, the soil most likely dries out, while the exterior ground varies throughout the year with changes in moisture and freezing. We did not incorporate freezing or varying properties into the model. We explored a range of soil thermal diffusivities (~3 to 8 × 10–7 m2/s [32.3 to 86.1 ×10–7 ft2/s]), representing dry, low thermal conductivity to wet, higher thermal conductivity soils. Floor surface effects such as carpets or other flooring, along with structures (tables) that radiatively block the floor’s view of other room surfaces have been examined, and we have found that their impact is not significant with the ground’s internal resistance dominating the situation.

this is the sixth in a series of columns. Find previous columns at www.ashrae.org/ashraejournal.
62	 ASHRAE	Journal	 ashrae.org	 	 February	 2011



ASHRAE Journal - February 2011

Table of Contents for the Digital Edition of ASHRAE Journal - February 2011

ASHRAE Journal - February 2011
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Thermal Coupling of Cooling and Heating Systems
10 Common Problems in Energy Audits
Hall of Fame Feature: History of the Changing Concepts in Ventilation Requirements
A Guide to Wireless Technologies
Building Sciences
Solar NZEB Project
Emerging Technologies
People
Special Section
InfoCenter
Commissioning
Products
Washington Report
Classified Advertising
Advertisers Index
ASHRAE Journal - February 2011 - ASHRAE Journal - February 2011
ASHRAE Journal - February 2011 - Cover2
ASHRAE Journal - February 2011 - 1
ASHRAE Journal - February 2011 - 2
ASHRAE Journal - February 2011 - Contents
ASHRAE Journal - February 2011 - Commentary
ASHRAE Journal - February 2011 - 5
ASHRAE Journal - February 2011 - Industry News
ASHRAE Journal - February 2011 - 7
ASHRAE Journal - February 2011 - Letters
ASHRAE Journal - February 2011 - 9
ASHRAE Journal - February 2011 - 10
ASHRAE Journal - February 2011 - 11
ASHRAE Journal - February 2011 - 12
ASHRAE Journal - February 2011 - 13
ASHRAE Journal - February 2011 - 14
ASHRAE Journal - February 2011 - 15
ASHRAE Journal - February 2011 - Meetings and Shows
ASHRAE Journal - February 2011 - 17
ASHRAE Journal - February 2011 - Thermal Coupling of Cooling and Heating Systems
ASHRAE Journal - February 2011 - 19
ASHRAE Journal - February 2011 - 20
ASHRAE Journal - February 2011 - 21
ASHRAE Journal - February 2011 - 22
ASHRAE Journal - February 2011 - 23
ASHRAE Journal - February 2011 - 24
ASHRAE Journal - February 2011 - 25
ASHRAE Journal - February 2011 - 10 Common Problems in Energy Audits
ASHRAE Journal - February 2011 - 27
ASHRAE Journal - February 2011 - 28
ASHRAE Journal - February 2011 - 29
ASHRAE Journal - February 2011 - 30
ASHRAE Journal - February 2011 - 31
ASHRAE Journal - February 2011 - 32
ASHRAE Journal - February 2011 - 33
ASHRAE Journal - February 2011 - Hall of Fame Feature: History of the Changing Concepts in Ventilation Requirements
ASHRAE Journal - February 2011 - 35
ASHRAE Journal - February 2011 - 36
ASHRAE Journal - February 2011 - 37
ASHRAE Journal - February 2011 - 38
ASHRAE Journal - February 2011 - 39
ASHRAE Journal - February 2011 - 40
ASHRAE Journal - February 2011 - 41
ASHRAE Journal - February 2011 - 42
ASHRAE Journal - February 2011 - 43
ASHRAE Journal - February 2011 - A Guide to Wireless Technologies
ASHRAE Journal - February 2011 - 45
ASHRAE Journal - February 2011 - 46
ASHRAE Journal - February 2011 - 47
ASHRAE Journal - February 2011 - 48
ASHRAE Journal - February 2011 - 49
ASHRAE Journal - February 2011 - Building Sciences
ASHRAE Journal - February 2011 - 51
ASHRAE Journal - February 2011 - 52
ASHRAE Journal - February 2011 - 53
ASHRAE Journal - February 2011 - 54
ASHRAE Journal - February 2011 - 55
ASHRAE Journal - February 2011 - 56
ASHRAE Journal - February 2011 - 57
ASHRAE Journal - February 2011 - 58
ASHRAE Journal - February 2011 - 59
ASHRAE Journal - February 2011 - 60
ASHRAE Journal - February 2011 - 61
ASHRAE Journal - February 2011 - Solar NZEB Project
ASHRAE Journal - February 2011 - 63
ASHRAE Journal - February 2011 - 64
ASHRAE Journal - February 2011 - 65
ASHRAE Journal - February 2011 - 66
ASHRAE Journal - February 2011 - 67
ASHRAE Journal - February 2011 - 68
ASHRAE Journal - February 2011 - 69
ASHRAE Journal - February 2011 - Emerging Technologies
ASHRAE Journal - February 2011 - 71
ASHRAE Journal - February 2011 - 72
ASHRAE Journal - February 2011 - 73
ASHRAE Journal - February 2011 - 74
ASHRAE Journal - February 2011 - 75
ASHRAE Journal - February 2011 - People
ASHRAE Journal - February 2011 - 77
ASHRAE Journal - February 2011 - InfoCenter
ASHRAE Journal - February 2011 - 79
ASHRAE Journal - February 2011 - 80
ASHRAE Journal - February 2011 - 81
ASHRAE Journal - February 2011 - 82
ASHRAE Journal - February 2011 - 83
ASHRAE Journal - February 2011 - 84
ASHRAE Journal - February 2011 - 85
ASHRAE Journal - February 2011 - Commissioning
ASHRAE Journal - February 2011 - 87
ASHRAE Journal - February 2011 - 88
ASHRAE Journal - February 2011 - 89
ASHRAE Journal - February 2011 - 90
ASHRAE Journal - February 2011 - Products
ASHRAE Journal - February 2011 - Washington Report
ASHRAE Journal - February 2011 - Classified Advertising
ASHRAE Journal - February 2011 - 94
ASHRAE Journal - February 2011 - 95
ASHRAE Journal - February 2011 - Advertisers Index
ASHRAE Journal - February 2011 - Cover3
ASHRAE Journal - February 2011 - Cover4
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