Paper Conference

Proceedings of Building Simulation 2009: 11th Conference of IBPSA

     

INFLUENCE OF GROUND HEAT EXCHANGER MODELLING ON THE PREDICTED EFFICIENCY OF THE HEAT PUMP SYSTEM

Wojciech Kozak, Joachim Seifert, Wolfgang Richter

DOI: https://doi.org/10.26868/25222708.2009.0623-630
Abstract: This paper presents simulations of the integral coefficients of performance of a heat pump system coupled with a vertical ground heat exchanger (GHE). The GHE is simulated using different assumptions concerning the heat transfer in the ground, heat exchange between the ground and the brine and vertical variation of the brine temperature. The differences in the predicted performance coefficients of the heat pump system using the GHE as the lower energy source are analysed and shown to be significant. NOMENCLATURE General cp - thermal capacity of ground in J / (kg × K) dl - length of GHE’s segment in m r₀,IN - inner radius of the GHE’s pipes in m r₀ - outer radius of the GHE’s pipes in m r₁ - borehole radius in m rMAX - maximal radius, the outer boundary in m rQ - dimensionless position of point heat source rS - dimensionless position of the image sink z - z-coordinate of the point source in m z’ - z-coordinate of the image sink in m Hm - length of the GHE in m Latin g - function q& - specific heat flux in W/m r - position relative to GHE’s centre in m rz - radial position of the calculation node in m t - time in s P - electrical power consumption in W Q& - heat flux in W R - thermal resistance in (m² K) / W T - temperature in °C Greek α - thermal diffusivity of the ground in m²/s β - integral coefficient of performance γ - γ = r / Hm η - η = z’ / Hm λ - thermal conductivity in W / (m × K) ρ - density of the ground in kg / m³ ξ - ξ = z / Hm Subscripts hp1 - beginning of the heating period hp2 - end of the heating period a - external i - internal init - initial condition sys - global property of the system A - auxiliary devices except for the pump of the heating system C - compressor Cont - control units HP - heat pump S - storage tank
Pages: 623 - 630
Paper:
bs2009_0623_630