Modeling and Design of Net ZEBs as Integrated Energy Systems - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 93

load (thermal annual imbalance), the highest monthly ground load, and the
peak hourly ground load, R 10y , R 1m , and R 6h are effective ground thermal
resistancescorrespondingto10years,onemonth,and6hgroundloads,and
R b is the effective borehole thermal resistance.
The three ground thermal resistances are calculated assuming a cylindrical
heat source solution in conjunction with temporal superposition (see
Philippe, Bernier, and Marchio (2010) for more details).
2.2.5 Combined Heat and Power (CHP) for Net ZEBs
Another important technology for Net ZEBs are combined heat and power
(CHP) systems, also known as cogeneration systems, or even trigeneration
systems ( Figure 2.26 ) (Dinçer and Rosen, 2002) when both useful heat and
cooling are produced inaddition toelectricity using renewable fuels,suchas
biomass/biogas. Cooling is usually done using absorption chillers.
Fig. 2.26 Schematic of trigeneration system
Usually, it is difficult to achieve Net ZEB status based on a site energy
balance for a house/building since the biomass usually has to be brought
from another site. However, cogeneration is a thermodynamically efficient
use of a renewable fuel and is dispatchable - that is, a CHP system can
be run when electricity is needed. Standard electricity production systems
discard some energy as waste heat whereas cogeneration systems use this
thermal energy.