4.1   Overview

The objective of the Building Energy Efficiency Standards (Energy Standards) requirements for mechanical systems is to reduce energy consumption while maintaining occupant comfort. These goals are achieved by:

1.    Maximizing equipment efficiency, both at design conditions and during part load operation

2.    Minimizing distribution losses of heating and cooling energy

3.    Optimizing system control to minimize unnecessary operation and simultaneous use of heating and cooling energy

The Energy Standards also recognize the importance of indoor air quality for occupant comfort and health. To this end, the Energy Standards incorporate requirements for outdoor air ventilation that must be met during all operating conditions.

This chapter summarizes the requirements for space conditioning, ventilating, and service water heating systems for non-process loads in nonresidential buildings. Chapter 10 covers process loads in nonresidential buildings and spaces.

This chapter is organized as follows:

Section 4.1 provides an overview of the chapter and the scope of the mechanical systems requirement in the Energy Standards.

Section 4.2 addresses the requirements for Heating, Ventilation, and Air Conditioning (HVAC) and service water heating equipment efficiency and equipment mounted controls.

Section 4.3 includes mechanical ventilation, natural ventilation, and demand controlled ventilation.

Section 4.4 covers construction and insulation of ducts and pipes, and duct sealing to reduce leakage.

Section 4.5 covers control requirements for HVAC systems including zone controls, and controls to limit reheating and recooling.

Section 4.6 covers the remaining requirements for HVAC systems; including sizing and equipment selection, load calculations, economizers, electric resistance heating limitation, limitation on air-cooled chillers, fan power consumption and fan and pump flow controls.

Section 4.7 covers the remaining requirements for service water heating.

Section 4.8 covers the performance method of compliance.

Section 4.9 covers compliance requirements for additions and alterations.

Section 4.10 covers the glossary, reference, and definitions.

Section 4.11 describes the mechanical plan check documents, which includes information that must be included in the building plans and specifications to show compliance with the Energy Standards, including the mechanical compliance documents.

Acceptance requirements apply at all times to the systems covered regardless of whether the prescriptive or performance compliance approach is used.

Chapter 12 describes mandated acceptance test requirements, which are summarized at the end of each section. The full acceptance requirements are in §120.5 of the Energy Standards and in the 2016 Reference Appendix NA7.

4.1.1    HVAC Energy Use

Mechanical and lighting systems are the largest consumers of energy in nonresidential buildings. The amount of energy consumed by various mechanical components varies according to system design and climate. For most buildings in lower elevation California climates, fans and cooling equipment are the largest components of energy consumed for HVAC purposes. Energy consumed for heating is usually less than fans and cooling, followed by service water heating.

Figure 4-1 – Typical Nonresidential Building Electricity Use

Heating, cooling and ventilation account for about 28% of commercial building electricity use in California.

Source IEQ RFP, December 2002, California Energy Commission No. 500-02-501.

4.1.2    Mandatory Measures

Mandatory measures, covered in §110.0-110.5 and §120.0-120.9, apply to all nonresidential buildings, whether the designer chooses the prescriptive or performance approach for compliance and include:

1.  Equipment certification and equipment efficiency - §110.1 and §110.2.

2.  Service water heating systems and equipment - §110.3.

3.  Spa and pool heating systems and equipment - §110.4.

4.  Restrictions on pilot lights for natural gas appliances and equipment - §110.5.

5.  Ventilation requirements - §120.1.

6.  Control requirements - §120.2.

7.  Pipe insulation - §120.3.

8.  Duct construction and insulation - §120.4.

9.  Acceptance tests in §120.5 and the 2016 Reference Appendices NA7.

10.  Commissioning - §120.8.

11.  Commercial Boilers - §120.9.

4.1.3    Prescriptive and Performance Compliance Approaches    

The Energy Standards allow mechanical system compliance to be demonstrated by meeting the mandatory requirements and the requirements of either the prescriptive or performance compliance approaches.  Prescriptive Compliance Approach

The measures in the prescriptive compliance approach, §140.4, cover specific requirements for individual components and systems that directly comply with the Energy Standards, including:

1.    Load calculations, sizing, system type and equipment selection - §140.4(a) and (b).

2.    Fan power consumption - §140.4(c).

3.    Controls to reduce reheating, recooling and mixing of conditioned air streams; - §140.4(d).

4.    Economizers - §140.4(e).

5.    Supply temperature reset - §140.4(f).

6.    Restrictions on electric-resistance heating - §140.4(g).

7.    Fan speed controls for heat rejection equipment - §140.4(h).

8.    Limitation on centrifugal fan cooling towers - §140.4(h).

9.    Minimum chiller efficiency - §140.4(i)

10.  Limitation on air-cooled chillers - §140.4(j).

11.  Hydronic system design - §140.4(k).

12.  Duct sealing - §140.4(l).

13.  Supply fan control - §140.4(m).

14.  Mechanical System Shut-off control - §140.4(n).  Performance Compliance Approach

The performance compliance approach, §140.1, allows the designer to trade off energy use in different building systems. This approach provides greater design flexibility but requires extra effort and a computer simulation of the building. The design must still meet all of the mandatory requirements.

Performance approach trade-offs can be applied to the following disciplines: mechanical, lighting, envelope, and covered processes. The performance approach requires creating two models using Energy Commission-certified compliance software:

1.    Base-case building energy model which meets all of the mandatory and prescriptive requirements.

2.    Proposed building energy model that reflects the proposed building design.

The proposed model complies if it has a lower TDV value than the base-case model.

The performance approach may only be used to model the performance of mechanical systems that are covered under the building permit application (see Section 4.8 and Chapter 11 for more detail).