Part 4 - HEATING, VENTILATING AND AIR CONDITIONING (HVAC) SYSTEMS

 

 

 

4.1    Scope

 

This section provides the minimum requirements for design, sizing and control of space conditioning by heating, cooling and ventilation equipment. These requirements are in addition to those provided in the Building Code of Pakistan.

 

4.2    System Design

 

4.2.1    System Sizing

 

For the purpose of sizing HVAC systems, the heating and cooling design loads shall include sensible and latent heat gain and loss from conduction, solar radiation, infiltration, ventilation and internal loads. The design loads shall be calculated according to the procedure described in the Building Energy Code Compliance Handbook or the procedures in the ASHRAE Handbook 1989 Fundamentals.

 

Interior and exterior design conditions shall be those shown in Appendix II.

 

4.2.2    Simultaneous Heating and Cooling:

 

Use of simultaneous heating and cooling by reheating or recooling supply air or by concurrent operation of independent heating and cooling system serving a common zone shall be restricted as below:

 

(a)    Recovered energy: Recovered energy in excess of the new energy expended in the recovery process may be used for the control of temperature and humidity.

 

(b)    New energy for humidity control: New energy may be used to prevent relative humidity from rising above 60 percent for comfort control.

 

(c)    New energy for temperature control: New energy may be used for temperature control if minimized in accordance with para 4.2.2.(c).1 through 4.2.2.(c).5.

 

1.  Reheat system: Systems employing reheat and servicing multiple zones, other than those employing variable air volume for temperature control, shall be provided with a control that will automatically reset the system cold air supply to the highest temperature level that will satisfy the zone requiring the coolest air. Single zone reheat systems shall be controlled to sequence reheat and cooling.

 

2.  Dual duct and multizone systems: These systems other than those employing variable air volume control, shall be provided with controls that will automatically reset:

 

a.  The cold deck air supply to the highest temperature that will satisfy the zone requiring the coolest air and

 

b.  The hot deck air supply to the lowest temperature that will satisfy the zone requiring the warmest air.

 

3.  Recooling System: Systems in which heated air is recoooled, directly or indirectly, to maintain space temperature shall be provided with control that will automatically reset the temperature to which the supply air is heated to the lowest level that will satisfy the zone requiring the warmest air.

 

4.  Multiple zones: For systems with multiple zones, one or more zones maybe chosen to represent a number of zones with similar heating/cooling characteristics. A multiple zone system that employs reheating or recooling for control of  not more than 2.3 6 m3/s  (5000ft3/min) or 20 percent of the total supply air of the system which ever is less, shall be exempt from the supply air temperature reset requirements ofparagraph4.2.2.(c).1 through 4.2.2.(c).5.

 

5.  Concurrent Operations: Concurrent operation of independent heating and cooling systems serving common spaces and requiring the use of new energy for heating and/or cooling shall be minimized by one or both of the following:

a.  By providing sequential temperature control of both heating and cooling capacity in each zone.

b.           By limiting the heat energy. input through automatic reset control of the heating medium temperature (or energy input rate) to only that necessary to offset heat loss due to transmission and infiltration and, where  applicable, to heat the ventilation air supply to the space.

 

4.2.3    Transport Energy:

 

(a)    All air system:

 

1.  The air transport factor for each all‑air HVAC system shall not be less than 8.0. The factor shall be based on design system air flow for constant volume systems. The factor for variable air volume systems may be based on average conditions of operations. Energy for transfer of air through heat recovery devices shall not be included in determining the factor: however, such energy shall be included in the evaluation of the effectiveness of the heat recovery system.

 

Air transport factor = Space Sensible Heat Removed/

    (Supply + Return Fan(a) Power Input)*

 

* Both expressed in same unite, either watts or Btu/h

 

 

2.  For purpose of these calculations, Space Sensible Heat Removed is equivalent to maximum coincident design sensible cooling load of all spaces for which the system provides cooling. Fan Power Input is the rate of energy delivered to the fan prime mover.

 

(b)    Other Systems:

 

Air and water, all‑water and unitary systems employing chilled, hot, dual temperature or condenser water transport systems to space terminals shall not require greater transport energy (including central and terminal fan power and pump power) than an equivalent all‑air system providing the space sensible heat removal and having an air transport factor not less than 8.0.

 

4.2.4    Balancing:

 

HVAC system design shall provide means for balancing air and water systems. In doing so, the consideration shall include, but not be limited to, dampers, temperature and pressure test connections and balancing valves.

 

4.2.5    Controls

 

4.2.5.1    Temperature Controls:

 

Each system shall be provided with at least one adjustable thermostat for the regulation of the temperature. Each thermostat shall be capable of being set by adjustment or selection of sensors as follows:

 

(a)  When used to control heating only: 13 C to 24 C (55 F to 75 F).

 

(b)  When used to control cooling only: 21 C to 29 C (70 F to 85 F).

 

(c)  When used to control both heating and cooling it shall be capable of being set from 13 C to 29 C (55 F to 85 F) and shall be capable of operating the system heating and cooling in sequence. The thermostat and/or control system shall have an adjustable dead band of upto 5.5 C (10 F) or more except as allowed in para 4.2.2. (c) .5. Dead band is defined as the temperature range in which no heating and cooling energy is used.

 

The recommended internal dry bulb temperature shall be 26 ^oC for summers and 21 ^oC for winters (see Appendix II).

 

4.2.5.2    Humidity Controls:

If a system is equipped with a means for adding moisture to maintain specific selected relative humidity’s in space or zones, a humidistat shall be provided. The humidistat shall be capable of being set to prevent new energy from being used to produce space‑relative humidity above 30 percent. When a humidistat is used in a system for controlling moisture removal to maintain specific selected relative humidity’s in spaces or zones, it shall be capable of being set to prevent new energy from being used to produce a space relative humidity less than 60 percent.

 

4.2.5.3    Zoning:

 

(a)  Multifamily Dwelling: For multifamily dwellings, each individual dwelling unit shall be considered separately and shall have at least one thermostat for regulation of space temperature.

 

(b)  All other types of buildings or occupancies: At least one thermostat for regulation of space temperature shall be provided for:

 

1.  each separate system

 

2.  each separate zone (see definitions). As a minimum each floor of a building shall be considered as a separate zone. In a multistory building where the perimeter system offsets ,only the transmission losses of exterior wall, an entire side of uniform exposure may be zoned separately. A readily accessible manual or automatic means shall be provided to balance the heating and/or cooling input to each floor.

 

c)    Control Setback and Shut‑off

 

1.  Multifamily Dwelling: The thermostat required in para  4.2.5.3(a) or an alternate means  including, but not limited to  switch or clock, shall provide a  readily accessible manual or  automatic means for reducing the  energy required for heating and  cooling during periods of non‑use  or reduced need including, but not  limited to, unoccupied periods and  sleeping hours. Lowering thermostat set points to reduce  energy consumption of heating  systems shall not cause energy to  be expended to reach the reduced  setting.

2.  Other Buildings and Occupancies: Each system shall be equipped with readily accessible means of shutting off or reducing the energy used during periods on non‑use or alternate uses of the building spaces or zones served by the system. The following are examples that meet requirement:

 

‑  Manually adjustable automatic timing devices

 

‑  Manual devices for use by operating personnel

 

‑  Automatic Control Systems

 

4.2.6    Mechanical Ventilation:

 

4.2.6.1    Switches and Dampers

 

Each mechanical ventilation system (supply and/or exhaust) shall be equipped with a readily accessible switch or other means for shut off or for volume reduction or shutoff when full ventilation is not required. Automatic or gravity dampers that close when the system is not operating shall be provided for outdoor air intake and exhausts. Automatic or manual dampers installed for the purpose of shutting off ventilation systems shall be designed with tight shutoff characteristics to minimize air leakage.

 

Exceptions: 1. Manual dampers for outdoor intakes may be used in the following cases:

 

a) For single and Multi­family residential buildings

 

b) Dampers are not required when ventilation air flow  is less  than 0.047m3 /S (100 ft3 /min).

 

4.2.6.2    Non‑Residential Kitchen Space

 

a. Non‑residential kitchen space must be designed with an exhaust air and make up air balance such that the space is never under a positive pressure, and never under a negative pressure exceeding .02 inch or 0.51 m.m. w.g. relative to all indoor spaces surrounding the kitchen space, during all cooking hours. NOTE: Makeup air in low volume exhaust hoods can be air that is conditioned by a unit dedicated to the hood exhaust system.

 

b. All exhaust and makeup air system components (fans, dampers, etc.) shall be interlocked in such a way that the balance prescribed in (a) above is maintained throughout all cooking hours, and all variations of cooking operations.

 

c. Net cooking exhaust from the kitchen space shall be the minimum possible consistent with positive performance, (i.e., capture, containment, and removal of all vapors and smoke produced in the cooking processes). Compensating hoods and reduced exhaust hoods should be listed or certified for lower net levels of exhaust, or have their, performance demonstrated to the local authority having jurisdiction, at maximum cooking levels.

 

 

4.2.7    Air Duct System:

 

4.2.7.1    Duct Construction:

 

All duct constructions shall be in accordance with Part 13 of the Building Code of Pakistan.

 

4.2.7.2    Duct Insulation

 

All ducts and plenums installed in or on buildings (except as indicated below) shall be thermally insulated.

 

(a)    All duct systems or portion thereof, shall be insulated to provide a thermal resistance as given in Tables 13.3, and 13.4 of the Building Code of Pakistan (Appendix III & IV).

 

Exceptions:  Duct insulation is not required in any of the following cases:

 

1.  Where delta t is 14C (25F) or less.

 

2.  When the heat gain or loss of the ducts, without insulation, will not increase the energy requirements of the buildings.

 

3.  Within HVAC equipment.

 

4.  Exhaust air ducts.

 

5.  Return Ducts installed within conditioned spaces.

 

6.  Ducts used exclusively for evaporative cooling systems.

 

(b)    The thermal resistance in para 4.2.7.2(a) does not consider condensation. Additional insulation with vapour barrier may be required to prevent condensation.

 

(c)    Except where ducts are installed in or beneath concrete slabs in residential buildings, the minimum installed insulation value for    Except where ducts are installed in or beneath concrete slabs in ducts in unconditioned space is

 

R=0.74m2     C/W (R=4.2 ft2 .h.F./Btu)

 

4.2.8    Pipe Insulation:

 

All piping installed to serve buildings and within buildings shall be thermally insulated.

 

4.2.8.1    Insulation Thickness

 

The minimum pipe insulation thickness shall be as per table 4.0.

 

Table 4.0

 

Minimum Pipe Insulation Thickness

 

*Pipe sizes are nominal dimensions. For piping exposed to ambient temperature, increase thickness by 0.5 in. or 13 m.m. In S.I. Units the pipes manufactured to sizes indicated or nearest size shall be used.

**Run outs to Individual Terminal Units (not exceeding 12 ft or 3.9 m. in length)

 

Exceptions:    Piping insulation is not required in the following cases:

 

(a) Piping installed within HVAC equipment

 

(b) Piping at fluid temperatures between 13C to 49C (55F to 120F) in condition spaces. In unconditioned spaces or outdoors, insulation shall be required.

 

(c) When the heat loss and/or heat gain of the piping, without insulation, does not increase the energy requirement of the buildings.

 

4.2.8.2    Other Insulation Thicknesses:

Insulation thicknesses in Table 4.0 are based on insulation having thermal resistance in the range of 0.028 to 0.032 m² C/W.mm (4.0 to 4.6 ft² h.F/ Btu.in) on a flat surface at a mean temperature of 24C (75F). Minimum insulation thickness shall be increased for materials haying R values less than 0.028 m² .C/W.mm (4 ft²  h.F/Btu.in) or may be reduced for materials having ?‑values greater than 0.032 m²  C/W.mm (4.6 ft²  h.F.Btu.in).

 

(a) For materials with thermal resistivity greater than 0.032 M2  C/W.mm (4.6 ft2 .h.F/But.in) the minimum insulation thickness may be reduced as follows:

 

New Minimum Thickness (in S.I. Units) = 0.032 x Thickness in table 3.3.9 / Actual R

 

New Minimum Thickness (in BTU Units = 4.6 x Thickness in table 3.3.9/Actual R

 

(b) For materials with thermal resistivity less than 0.028 M2 .C/ W.MM (4.0 ft2 .h.F/Btu.in) minimum insulation thickness shall be increased as follows:

 

New Minimum Thickness (S.I. Units )= 0.028 x Thickness in table 3.3./ Actual R

 

New Minimum Thickness (Btu. Units )= 4.0 x Thickness in table 3.3./Actual R

 

 

 

4.2.8.3    Insulation for Condensation

 

The required minimum thicknesses do not consider condensation. Additional insulation with vapour barriers may be required to prevent condensation.

 

4.3    System and Component Efficiency

 

This section deals with the requirements of the equipment arid mechanical component performance for heating, ventilating and air conditioning systems. It specifies the equipment and component efficiency levels. Suppliers of HVAC system equipment and components should furnish upon request by the system designers, contractors or prospective purchasers the inputs) and outputs) of all such HVAC products, based on new equipment and ARI rating conditions, and should cover full load, partial load and standby conditions as required. This shall be used to determine their compliance under this code. The information should also include performance data under other modes of operation and at ambient conditions necessary to make detailed analysis in case of deviation from the specific design criteria under this code.

 

4.3.1    Electric Packaged Equipment (Cooling Mode)

 

The requirements in this section apply to, but are not limited ,to, unitary (central) cooling equipment; packaged systems with air cooled, water‑cooled and evaporatively‑cooled condensers; the cooling mode ,of unitary and packaged terminal heat pumps; air source and water source heat pumps: packaged terminal air conditioners: and room air conditioners.

 

Exception. These requirements do not apply to equipment serving areas such as refrigerated food display cases or other equipment contributing a large amount of heat to the area served.

 

The equipment standards rating conditions shall be as specified in table 4.1. The energy efficiency ratio (EER) of the equipment and the coefficient of performance (C.O.P) as defined below shall be not less than specified in table 4.2.

 

Table 4.1

Rating Conditions For Packaged Equipment

 

 

 

Table 4.2 Minimum C.O.P/EER

Cooling (Performance at sea level)

 

 

 

 

Coefficient of Performance (COP) for packaged equipment in cooling mode is the ratio of the rate of net heat removal to the rate of total on‑site energy input to the air conditioner, expressed in consistent units and under designated rating conditions. (Table 4.1)

 

The rate of net heat removal shall be defined  as the change in total heat content of the  air entering and leaving the  equipment  (without reheat).

 

The total on‑site energy input shall be  determined by combining the energy  inputs to  all elements supplied with the package of the  equipment, including but not limited to,  compressor(s), compressor sump  heater(s) ,  pump(s), supply air fan (s), return air  fan(s), condenser air fan(s), cooling‑tower  fan(s), circulating water pumps) and the , HVAC system equipment control circuit. 

 

4.3.2    Electrically Operated HVAC System Components  (Cooling Mode)

HVAC system components where energy input is  entirely electric shall have standard rating  conditions and energy efficiency ratios and  C.O.P. as indicated in .the following tables: