EnergyTransfer results evaluation

Hi everyone,

I wanted to bring up some issues I encountered while analyzing the EnergyPlus results from my simulations in DesignBuilder.

Let me provide a brief overview of the model: It’s a three-storey office building (2315 m2 and 6327 m3) located in a cold climate with temperatures dropping to -35°C. The building operates from 8:00 to 18:00, Monday to Saturday, aiming for a comfortable indoor temperature range of 20-22°C. The building incorporates a PV system on both the roof and facade.

The heating system consists of an electric boiler and an air-to-water heat pump connected to radiators via a heat exchanger. Additionally, there is an underground water-to-water heat pump connected to the ventilation heating coil. Cooling is available but currently disabled for this analysis.

Currently, I am examining the simulation results for the heating period from September 1 to May 31, comparing two mechanical ventilation concepts in DesignBuilder:

  • AHU with recirculation (Proportional and economizer (Lockout with compressor)) featuring a Heating Recovery Unit (plate exchanger with 70% efficiency).
  • Simple AHU with an extract fan. The decision to include the HRU was made due to increased electricity consumption and inconsistent temperature conditions.

During my analysis, I referred to the following EnergyPlus tables:

  • Annual and Peak Values – Electricity
  • Annual and Peak Values – Other
  • Annual Building Sensible Heat Gain Components

My results and HVAC design Energy-Transfer2805 hosted at ImgBB — ImgBB

As I reviewed the results, I came across some questions, particularly regarding the EnergyTransfer parameters:

  1. 23293 and 48696 kWh - For the LoopToLoop EnergyTransfer parameter, I observed negative values. According to EnergyPlus documentation (p. 1070, 1.25.21 HeatExchanger:FluidToFluid), negative heat transfer indicates energy extraction from the demand side of the loop and addition to the supply side. However, my loop is configured differently. I noticed a correlation between LoopToLoop and Boiler EnergyTransfer when increasing the boiler temperature from 60 to 80°C. I wonder if this LoopToLoop EnergyTransfer parameter affects the final energy balance or if it represents losses between the consumption and supply loop of the heat exchanger.
  2. 8981 and 14763 kWh - The values obtained by subtracting the totals of Radiant Heating Demand and EnergyTransfer from the Boiler and AWHP. I’m uncertain how to categorize these values and assign them specific meanings in the analysis.
  3. When combining Heating and Ventilation EnergyTransfer parameters such as Cooling and Heating EnergyTransfer and EnergyTransfer Plant, I obtained the EnergyTransfer Facility value. I assume this represents the energy from internal gains within the building envelope. Can you provide further details on how to describe these types of EnergyTransfer?
  4. 89936 и 161281 kWh - In the results tables, I did not find any specific values for Mechanical Ventilation Loss when I added all the Sensible Cooling Load Components and subtracted the EnergyTransfer Facility. I’m unsure if I’m properly identifying and designating these values to achieve an accurate energy balance.
  5. 169456 kWh - Lastly, I noticed a significantly high value related to heat recovery. Is this value plausible? When considering all Internal Heat Gains and AHU Heating (250550 kWh), the heat recovery accounts for 67.6% of the total. I’d appreciate clarification on whether such a large heat recovery value is feasible.

Thank you for your assistance in addressing these questions.