GLOSSARY OF TERMS
Hours of operation:
The hours during the day when the building is ventilated with outdoor air—typically the time when the building is occupied.
Days per week:
Days per week that the building is ventilated with outdoor air.
CFM of outdoor air:
The rate of outdoor air ventilation during the hours of operation..
Expected cost for electricity in $/kWh. (Default $.08/kWh)
Peak Demand Charge:
Expected electric demand charge in $/kW. (Default: $10/kW)
Months of Peak Demand Charge:
The number of months the utility assesses a demand charge during the year. (Default: 6 months)
Expected cost for gas in $/therm. (Default: $1/therm)
The heating efficiency for the heating system. (Default: 80%)
The cooling efficiency rating for the HVAC system. (Default is 10 EER.)
Airxchange Wheel Total Effectiveness:
Airxchange total energy recovery wheels generally recover 70% of the difference in sensible and latent energy (total energy) between the building exhaust and incoming ventilation air streams.This effectiveness can vary depending on the system.
HVAC Fan Power (% of Total System):
In most DX systems, fan power represents approximately 15% of total energy consumption. Energy Recovery ventilation enables a smaller DX system to be installed. As a result, significant operating savings can be attributed to operating a smaller fan in the smaller system.
Installed Cost per Ton:
Estimated installed cost for the HVAC system on a per ton basis.
Installed Cost per cfm for ERV:
The installed cost for the energy recovery system. This number will vary depending on size and system design. $4 per cfm is a general average but may vary between $2 and $6 per cfm.
Airxchange Wheel Cooling Capacity:
Airxchange energy recovery wheels provide significant cooling capacity. Consequently, a system with energy recovery will require less mechanical tonnage than one without.
Airxchange Wheel Heating Capacity:
Airxchange energy recovery wheels provide significant heating capacity. Consequently, a system with energy recovery will require less mechanical mbh capacity than one without.
Peak Demand Reduction:
The cooling capacity reduction also translates into reduced peak demand (kW), which in turn reduces operating cost and may qualify for utility rebates.
Annual Cooling Energy Saved:
Estimate of savings in kWh of using a system with energy recovery versus one without.
Annual Heating Energy Saved:
Estimate of savings in mbtu of using a system with energy recovery versus one without.
Cooling Operating Cost (Savings):
Estimated net change in annual operating cost that energy recovery contributes during the cooling season.
Heating Operating Cost (Savings):
Estimated net change in annual operating cost that energy recovery contributes during the heating season.
Cost (Savings) to operate smaller unit fan:
When a DX/ERV system is properly right sized, there are operating savings for the resulting smaller system fan. The system fan generally represents 15% of the total system energy consumption. This variable can be adjusted in the input section.
Cost (Savings) to run ERV fan:
An energy recovery wheel increases static pressure on the HVAC system. Fan power is necessary to overcome this static pressure. The program estimates the cost to operate those fans with approximately 0.8 inches of pressure drop across the wheel.
Cost of HVAC Unit:
An HVAC unit with energy recovery will have smaller mechanical capacity than one without energy recovery. This field estimates the incremental first cost reduction from installing this smaller mechanical system. It is critical that systems be right sized with energy recovery in order to maximize payback as well as overall performance.
Cost of ERV:
Estimated incremental cost to add energy recovery ventilation to the system.
Net Capital Expenditure:
Cost of HVAC added with Cost of ERV
Net Capital Expenditure divided by Annual Operating Savings.
Operating Savings divided by Net Capital Expenditure
This program is designed to generate an estimate of the energy savings potential for ERV systems that utilize Airxchange energy recovery wheels.
The program uses ASHRAE weather data and standard ASHRAE design days for the cities listed.
This program was developed to allow a user to easily and quickly generate estimates of savings available and the resulting financial metrics. It is not a replacement for energy modeling software and should not be used in lieu of more sophisticated engineering calculations. Airxchange’s performance and selection software should be utilized for performance analysis of a specific application.