| 1. |
- Monzó, Patrcia, et al.
(författare)
-
A monthly based bore field sizing methodology with applications to optimum borehole spacing
- 2016
-
Ingår i: ASHRAE Transactions. - : ASHRAE. - 0001-2505. ; 122:1, s. 111-126
-
Tidskriftsartikel (refereegranskat)abstract
- The required length of vertical ground heat exchangers(GHX) used in ground-coupled heat pump (GCHP) systems isdetermined so that the outlet temperature from the GHXremains within certain limits for the worst ground load condi-tions. These conditions may not necessarily occur after 10 or20 years of operation, as is usually assumed, but often occurduring the first year of operation.The primary objective of this paper is to develop a generalmethodology for the calculation of the total required bore fieldlength on a monthly basis during the first year of operationusing the framework of the ASHRAE bore field sizing method.Itisathreephaseprocess.Thefirstphaseconsistsofanalyzingandorderinggroundloadsaccordingtothefirstmonthofoper-ation.Next,afirstsetofrequiredlengthsisdeterminedbyusingthe analyzed ground load components and assuming atemperaturepenaltyTp=0.Then,aniterativeprocesstocalcu-latethetemperaturepenaltyattheendofeachmonthiscarriedout to obtain the final required length for the worst conditions.The methodology is exemplified in a particular case witha slight annual cooling thermal imbalance and with a highinfluence of the hourly peak in heating. For this particularcase, it is shown that the required bore field length occursduring the first year and that the starting month of operationhas a strong influence on the results.Finally,itisshownthatitispossibletoreducetheboreholespacing when the annual ground load is quasibalanced. In thecase studied here, the minimum length occurs for a borehole-to-borehole spacing of about 3.2 m (10.50 ft)
|
|
| 2. |
- Monzó, Patrcia, et al.
(författare)
-
A study of the thermal response of a borehole field in winter and summer
- 2013
-
Konferensbidrag (refereegranskat)abstract
- A Ground Source Heat Pump system is a well-known technology used to provide space heating and cooling in residential and commercial buildings. For large energy demands, a number of boreholes, which can vary between tens and hundreds, may be required. The boreholes can be arranged in linear, square, rectangular, or any other configuration not necessarily symmetric. The heat exchangers in the boreholes are typically connected in parallel. Recently, the idea of a more flexible configuration of multiple Borehole Heat Exchangers (BHEs) has been introduced in commercial applications, enabling the system to operate in a more versatile manner, dividing the ground into different thermal zones. In this new arrangement, the BHEs are connected into thermal sub-groups allowing them to operate separately as sub-systems, depending on the building energy needs and the seasonal periods. In this project, the temperature response of a multiple BHE configuration is obtained from simulations in a numerical model using FEM software, Comsol Multiphysics© under different operational conditions. First, the loads are imposed under the usual conditions so that all boreholes are operated to provide heating in winter and cooling in summer. The results of this study show that our numerical model presents a good agreement with the ones generated from EED when the system is balanced. Moreover, some hypothetical scenarios with respect to the BHEs arrangement and the operational mode are performed thanks to the flexibility of our numerical model. The hypothetical scenarios provide a first approach about the thermal behavior of the boreholes and their interactions within the field with respect to its wall temperature, previous operation and thermal storage. Further work will be devoted to study more realistic scenarios.
|
|
| 3. |
- Monzó, Patrcia, et al.
(författare)
-
Numerical generation of the temperature response factors for a borehole heat exchanger field
- 2013
-
Ingår i: Numerical generation of the temperature response factors for a borehole heat exchanger field.
-
Konferensbidrag (refereegranskat)abstract
- Ground Coupled Heat Pump (GCHP) systems connected to a set of vertical ground heat exchangers require short and long term dynamic analysis of the surrounding ground for an optimal operation. The thermal response of the ground for a multiple Borehole Heat Exchanger (BHE) field can be described by proper temperature response factors or “g-functions”. This concept was firstly introduced by Eskilson (1987). The g-functions are a family of solutions of the transient heat conduction equation and each of them refer to a given borehole field geometry. Furthermore the g-functions are the core of many algorithms for simulating the ground response to a GCHP system, including the well-known commercial software EED.Analytical approaches based on the Finite Line Source (FLS) model have been developed by Eskilson (1987), Zeng et al. (2002) and later by Lamarche (2007). Such solutions can be in principle applied together with space superposition to infer the thermal response for any BHE configuration.This study is a continuation of the previous work presented in Acuña et al. (2012), and a further investigation is devoted to optimize a numerical model of a squared configuration of 64 boreholes using the commercial software Comsol Multiphysics©. Symmetry conditions and different Fourier numbers have been applied and explored together with the effects related to the dimensions of the calculation domain with respect to the BHE depth and BHE field width. Furthermore, a parametric analysis is addressed to boundary conditions, which points out possible limits on the calculation domain extension. The results of the proposed numerical model are compared with the g-functions embedded within the EED software as well as those calculated by FLS method through the spatial superposition. In a closer approximation to reality, the numerical model is also studied accounting for an adiabatic part at the top of the BHE.
|
|
