Thermal system with exhaust heat exchanger

Abstract

A thermal system for providing thermal conditioning to a facility includes a facility air circuit for circulating a facility air throughout the facility and a downhole fluid circuit for circulating a downhole fluid. The facility air circuit is thermally connected to a heat pump for exchanging heat with the facility air. The downhole fluid circuit includes the heat pump for exchanging heat with the downhole fluid, a main loop, including a borehole heat exchanger (BHE) for exchanging heat between the downhole fluid and a geological formation, and an exhaust loop including an exhaust heat exchanger coupled to an exhaust of the facility air circuit, wherein the exhaust loop is configured to circulate at least some of the downhole fluid through the exhaust heat exchanger to exchange heat between the downhole fluid and an exhaust flow of the facility air exhausted from the facility at the exhaust.

What is claimed is: 
     
         1 . A thermal system for providing thermal conditioning to a facility, including:
 a facility air circuit for circulating a facility air throughout the facility, the facility air circuit being thermally connected to a heat pump for exchanging heat with the facility air; and   a downhole fluid circuit for circulating a downhole fluid, comprising:
 the heat pump for exchanging heat with the downhole fluid; 
 a main loop, including a borehole heat exchanger (BHE) for exchanging heat between the downhole fluid and a geological formation; and 
 an exhaust loop including an exhaust heat exchanger coupled to an exhaust of the facility air circuit, wherein the exhaust loop is configured to exchange heat between the downhole fluid and an exhaust flow of the facility air exhausted from the facility at the exhaust. 
   
     
     
         2 . The thermal system of  claim 1 , wherein the exhaust loop is configured to circulated at least some of the downhole fluid to the exhaust heat exchanger. 
     
     
         3 . The thermal system of  claim 1 , further comprising a fluid distribution device included in the downhole fluid circuit for distributing the downhole fluid between the main loop and the exhaust loop, wherein the fluid distribution device includes one or more of an actuatable valve or a pump. 
     
     
         4 . The thermal system of  claim 3 , wherein the fluid distribution device is configured to dynamically modulate the circulation of the downhole fluid such that a portion of the downhole fluid flows to the exhaust loop and a portion of the downhole fluid flows through the main loop. 
     
     
         5 . The thermal system of  claim 1 , wherein the exhaust heat exchanger is connected to the main loop via the exhaust loop in series between an outlet of the heat pump and an inlet of the BHE such that the downhole fluid flows from the outlet of the heat pump, through the exhaust heat exchanger via the exhaust loop, and to the inlet of the BHE. 
     
     
         6 . The thermal system of  claim 3 , further comprising:
 one or more downhole temperature sensors for measuring one or more downhole fluid temperatures at one or more of an inlet of the BHE, an outlet of the BHE, an inlet of the heat pump, an outlet of the heat pump, an inlet of the exhaust loop, or an outlet of the exhaust loop;   one or more air temperature sensors for measuring one or more air temperatures of one or more of an inlet of the exhaust heat exchanger, or an outlet of the exhaust heat exchanger; and   a controller for controlling the fluid distribution device to distribute the downhole fluid between the exhaust loop and the BHE based on the one or more downhole fluid temperatures, the one or more air temperatures, or both.   
     
     
         7 . The thermal system of  claim 6 , wherein the controller is configured to distribute the downhole fluid to the exhaust loop based on the downhole fluid temperature at the outlet of the exhaust loop being a threshold difference from the downhole fluid temperature at the outlet of the heat pump. 
     
     
         8 . The thermal system of  claim 1 , wherein the exhaust loop includes a bypass line for selectively connecting the exhaust heat exchanger to the heat pump to bypass the BHE, and wherein the bypass line includes a bypass fluid distribution device for selectively directing the downhole fluid to the bypass line. 
     
     
         9 . The thermal system of  claim 1 , wherein the facility air circuit is configured to exchange heat directly with the heat pump. 
     
     
         10 . The thermal system of  claim 1 , further comprising facility fluid circuit for exchanging heat between the heat pump and the facility air via a facility fluid of the facility fluid circuit. 
     
     
         11 . The thermal system of  claim 1 , wherein the main loop and the exhaust loop are connected in parallel to the heat pump via decoupling manifolds, and wherein the main loop and the exhaust loop each include one or more fluid distribution devices for independently controlling a flowrate of the respective loops for exchanging heat with the heat pump at independent flowrates. 
     
     
         12 . A method of operating a thermal system, comprising:
 thermally conditioning a facility including facility air using a heat pump;   exhausting at least some of the facility air from the facility as an exhaust flow of the facility fluid; and   passing the exhaust flow through an exhaust heat exchanger to exchange heat between the exhaust flow and a downhole fluid of a downhole fluid circuit to recover at least some heating or cooling of the facility fluid to the downhole fluid.   
     
     
         13 . The method of  claim 12 , further comprising circulating the downhole fluid through the downhole fluid circuit to exchange heat between the downhole fluid and the heat pump. 
     
     
         14 . The method of  claim 13 , further comprising circulating the downhole fluid through a borehole heat exchanger (BHE) positioned in a geological formation to exchange heat between the heat pump and the geological formation. 
     
     
         15 . The method of  claim 14 , further comprising circulating the downhole fluid between the exhaust heat exchanger and the heat pump to exchange heat between the exhaust flow and the heat pump. 
     
     
         16 . The method of  claim 15 , further comprising circulating the downhole fluid without circulating the downhole fluid in the BHE. 
     
     
         17 . The method of  claim 14 , further comprising circulating the downhole fluid between the exhaust heat exchanger and the BHE to exchange heat between the exhaust flow and the geological formation without exchanging heat at the heat pump. 
     
     
         18 . The method of  claim 14 , further comprising:
 circulating the downhole fluid between the exhaust heat exchanger and a decoupling tank of the downhole fluid circuit at a first flowrate to exchange a first heat between the exhaust flow and an energy storage of the decoupling tank;   circulating the downhole fluid between the BHE and the decoupling tank at a second flow rate to exchange a second heat between the geological formation and the energy storage of the decoupling tank; and   circulating the downhole fluid between the decoupling tank and the heat pump to exchange a third heat between the energy storage of the decoupling tank and the heat pump.   
     
     
         19 . A thermal system for providing thermal conditioning to a facility, including:
 a facility air circuit for circulating a facility air throughout the facility, the facility air circuit being thermally connected to a heat pump for exchanging heat with the facility air; and   a downhole fluid circuit for circulating a downhole fluid, comprising:
 the heat pump for exchanging heat with the downhole fluid; 
 a borehole heat exchanger (BHE) for exchanging heat between the downhole fluid and a geological formation; and 
 an exhaust heat exchanger coupled to an exhaust of the facility air circuit and configured to exchange heat between the downhole fluid and an exhaust flow of the facility air exhausted from the facility at the exhaust; 
 wherein the downhole fluid circuit is configured to operate in a plurality of modes, including:
 a first mode for exchanging heat between the geological formation via the BHE and the heat pump; 
 a second mode for exchanging heat between the exhaust flow via the exhaust heat exchanger, the geological formation via the BHE, and the heat pump; 
 a third mode for exchanging heat between the exhaust flow via the exhaust heat exchanger and the heat pump. 
 
   
     
     
         20 . The system of  claim 19 , wherein the downhole fluid circuit is further configured to operate in a fourth mode for exchanging heat between the exhaust flow via the exhaust heat exchanger and the geological formation via the BHE.