Patent ID: 7113888

Claim:
A performance prediction program for a ground source heat pump system having a plurality of buried tubes as heat exchangers and a computer functioning by the program, wherein the computer comprises: a dimensionless distance calculating means for calculating a dimensionless distance (r*) by non-dimensionalizing a radial distance (r) from one of said plurality of buried tubes using the following expression (1); r * = r r p expression ⁢ ⁢ ( 1 ) where r p : radius of buried tube r: radial distance from buried tube a first dimensionless time calculating means for non-dimensionalizing the following expression (2) using a dimensionless time t* equal to at/r p and a dimensionless temperature T* equal to λT/(r p ·q) when an underground temperature (T S ) for any distance (r) from a predetermined one of said plurality of buried tubes within an elapsed time (t) is given by said expression (2), and which calculates a first dimensionless time (t 1 *) bounded by a zero segment in which said dimensionless temperature shows no change for said dimensionless distance and a linear increase segment in which said dimensionless temperature linearly increases for said dimensionless time; T s ⁡ ( r , t ) = 2 π ⁢ ⁢ λ s ⁢ ∫ 0 t ⁢ q ⁡ ( t ) ⁢ I ⁡ ( r , t ) ⁢ ⁢ ⅆ t ⁢ ⁢ where ⁢ ⁢ I ⁡ ( r , t ) = ⁢ ∫ 0 ∞ ⁢ ( 1 - ⅇ - au 2 t ) ⁢ J 0 ⁡ ( u ⁢ ⁢ r ) ⁢ Y 1 ⁡ ( u r p ) - Y 0 ⁡ ( u ⁢ ⁢ r ) ⁢ J 1 ⁡ ( u r p ) u 2 ⁡ [ J 1 2 ⁡ ( u r p ) + Y 1 2 ⁡ ( u r p ) ] ⁢ ⁢ ⅆ u expression ⁢ ⁢ ( 2 ) a: thermal diffusivity of the ground q: heat flow on the surface of buried tube λ s : thermal conductivity of the soil u: eigenvalue J x : the X root of the Bessel function of the first kind Y x : the X root of the Bessel function of the second kind a second dimensionless time calculating means for calculating a second dimensionless time (t 2 *) bounded by a logarithmic increase segment in which said dimensionless temperature for said dimensionless distance logarithmically increases and said linear increase segment; a boundary time acquiring means for obtaining an elapsed time corresponding to said first dimensionless time as a first boundary time (t′) and an elapsed time corresponding to said second dimensionless time as a second boundary time (t″); an underground temperature change calculating means for acquiring said first boundary time and said second boundary time, and for calculating an underground temperature change at any point for a distance between said plurality of buried tubes r d by the following approximate expression (3); and T s ⁡ ( r , t ) ≅ ⁢ T s ⁡ ( r , t ″ - t ′ ) + T s ⁡ ( r , t ′ - t ″ ) ≅ ⁢ - 2 πλ s ⁡ ( t 2 * - t 1 * ) ⁢ ∫ t 1 * t 2 * ⁢ q ⁢ ⁢ ⅆ t * - 2 πλ s ⁢ r * ⁢ 2 ⁢ T s * ⁢ ❘ r * = 1 t * - t 2 * expression ⁢ ⁢ ( 3 ) a tube surface temperature change calculating means for calculating an underground temperature change on a surface of said plurality of said buried tubes by a summation of said underground temperature changes for respective buried tubes.