3.7.6.6 Heat Recovery

90.1-2016 BM

Exhaust to Outside Heat Recovery Effectiveness

Applicability

Any system with outside air heat recovery

Definition

The effectiveness of an air-to-air heat exchanger between the building exhaust and entering outside air streams. Effectiveness is defined as follows:

(Equation 3.7.6-14)

$$HREFF = \frac{EEA_{db}-ELA_{db}}{EEA_{db}-OSA_{db}}$$

where

HREFF

The air-to-air heat exchanger effectiveness

EEAdb

The exhaust air dry-bulb temperature entering the heat exchanger

ELAdb

The exhaust air dry-bulb temperature leaving the heat exchanger

OSAdb

The outside air dry-bulb temperature

Units

Ratio

Input Restrictions

As designed

Baseline Rules

Required for fan systems with a design supply air flow rate of 5,000 cfm or greater if the minimum outside air quantity is 70% of the design air flow rate. If required, the energy recovery system should have at least 50% effectiveness. Energy recovery is not required for the following situations:

  • Systems serving spaces that are not cooled and that are heated to less than 60°F.
  • Systems exhausting toxic, flammable, paint, or corrosive fumes or dust. This exception shall only be used if heat recovery is not used in the proposed design.
  • Commercial kitchen hoods used for collecting and removing grease vapors and smoke classified as Type 1 my NFPA 96. This exception shall only be used if heat recovery is not used in the proposed design.
  • Heating systems in climate zones 1 through 3
  • Cooling systems in climate zones 3c, 4c, 5b, 5c, 6b, 7 and 8
  • Where the largest source of air exhausted at a single location at the building exterior is less than 75% of the design outdoor air flow rate. This exception shall only be used if heat recovery is not used in the proposed design.
  • Systems requiring dehumidification that employ energy recovery in series with the cooling coil. This exception shall only be used if heat recovery is not used in the proposed design.

 

Condenser Heat Recovery Effectiveness

Applicability

Systems that use recover heat from a condenser

Definition

The percentage of heat rejection at design conditions from a DX or heat pump unit in cooling mode that is available for space or water heating.

Units

Percent (%)

Input Restrictions

As designed. The software must indicate that supporting documentation is required on the output forms if heat recovery is specified.

Baseline Rules

Not applicable for most conditions. Condenser heat recovery is required for service water heating in 24-hour-per-day facilities, if the total installed heat rejection of the water cooled system exceeds 6,000,000 Btu/h and the design service water heating load exceeds 1,000,000 Btu/h.

In this case the heat recovery system is required to have the capacity to provide the smaller of 60% of peak heat rejection load at design conditions or preheat the peak service hot water to 85F.

Exceptions to this requirement do not apply.

If a condenser heat recovery system meeting the requirements described in Section 6.5.6.2 cannot be modeled, the requirement for including such a system in the actual building shall be met as a prescriptive requirement in accordance with Section 6.5.6.2, and no heat-recovery system shall be included in the proposed or baseline building designs.

 

Heat Recovery Use

Applicability

Systems that use heat recovery

Definition

The end use of the heat recovered from a DX or heat pump unit. The choices are:

  • Reheat coils
  • Water heating

Units

List (see above)

Input Restrictions

As designed. The software must indicate that supporting documentation is required on the output forms if heat recovery is specified.

Baseline Rules

Not applicable for most conditions. The end use will be water heating if required for 24-hour facility operation.