Ordenación y manejo de las Cuencas de los ríos: Pasto, Guamuez, Bobo, Juanambú,

prevent

a. Reheating b. Recooling

c. Mixing or simultaneously supplying air that has been previously mechanically heated and air that has been previously cooled, either by mechanical cooling or by economizer, and

d. Other simultaneous operation of heating and cooling systems to the same zone.

Exceptions:

a. Zones for which the volume of air that is reheated, recooled, or mixed is less than the larger of the following:

1. 30% of the zone design peak supply rate; 2. The outdoor airflow rate required to meet the

ventilation requirements of Section 6.2 of ASHRAE Standard 62.1 for the zone;

3. Any higher rate that can be demonstrated, to the

Standard 90.1-10 provides two exceptions for reheat that allow the designer to use reheat if it can be shown that the annual system energy use can be reduced by using a higher air flow rate. The 2012 IECC does not have this exception.

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2012 IECC Standard 90.1-10 Comparative Notes

1. Zones where special pressurization relationships or cross-contamination requirements are such that VAV systems are impractical.

2. Zones or supply air systems where at least 75 percent of the energy for reheating or for providing warm air in mixing systems is provided from a site- recovered or site-solar energy source.

3. Zones where special humidity levels are required to satisfy process needs.

4. Zones with a peak supply air quantity of 300 cfm (142 L/s) or less and where the flow rate is less than 10 percent of the total fan system supply airflow rate. 5. Zones where the volume of air to be reheated, recooled or mixed is no greater than the volume of outside air required to meet the minimum ventilation requirements of Chapter 4 of the International

Mechanical Code.

6. Zones or supply air systems with thermostatic and humidistatic controls capable of operating in sequence the supply of heating and cooling energy to the zones and which are capable of preventing reheating, recooling, mixing or simultaneous supply of air that has been previously cooled, either mechanically or through the use of economizer systems, and air that has been previously mechanically heated.

satisfaction of the authority having jurisdiction, to reduce overall system annual energy losses through a reduction in outdoor air intake for the system.

4. The air flow rate required to comply with applicable codes or accreditation standards, such as pressure relationships or minimum air change rates.

b. Zones that comply with all of the following:

1. The air flow rate in dead band between heating and cooling does not exceed the larger of the following:

i. 20% of the zone design peak supply rate; ii. The outdoor air flow rate required to meet the

ventilation requirement of Section 6.2 of ASHRAE 62.1 for the zone;

iii. Any higher rate that can be demonstrated, to the satisfaction of the authority having jurisdiction, to reduce overall system annual energy usage by offsetting reheat/recool energy losses through a reduction in outdoor air intake.

2. The air flow rate that is reheated, recooled, or mixed in peak heating demand shall be less than 50% of the zone design peak supply rate.

3. Airflow between dead band and full heating or full cooling shall be modulated.

c. Laboratory exhaust systems that comply with 6.5.7.2 d. Zones where at least 75% of the energy for reheating or

for providing warm air in mixing systems is provided from a site-recovered (including condenser heat) or site- solar energy source.

C403.4.5.1 Single duct variable air volume (VAV) systems, terminal devices. Single duct VAV systems shall use terminal devices capable of reducing the supply of primary supply air before reheating or recooling takes place.

No Comparable Provision Standard 90.1-10 does not include provisions specifically for single duct VAV systems and a further analysis should be done on Section 6.5.2.1 to

determine if it meets the intent of the 2012 IECC. C403.4.5.2 Dual duct and mixing VAV systems,

terminal devices. Systems that have one warm air duct and one cool air duct shall use terminal devices which are capable of reducing the flow from one duct to a minimum before mixing of air from the other duct takes place.

No Comparable Provision Standard 90.1-10 does not include provisions specifically for single duct VAV systems and a further analysis should be done on Section 6.5.2.1 to

59

2012 IECC Standard 90.1-10 Comparative Notes

C403.4.5.3 Single fan dual duct and mixing VAV systems, economizers. Individual dual duct or mixing heating and cooling systems with a single fan and with total capacities greater than 90,000 Btu/h [(26 375 W) 7.5 tons] shall not be equipped with air economizers.

No Comparable Provision Standard 90.1-10 does not include provisions specifically for single duct VAV systems and a further analysis should be done on Section 6.5.1 and 6.5.2.1 to determine if it meets the intent of the 2012 IECC. C403.4.5.4 Supply-air temperature reset controls.

Multiple zone HVAC systems shall include controls that automatically reset the supply-air temperature in response to representative building loads, or to outdoor air temperature. The controls shall be capable of resetting the supply air temperature at least 25 percent of the difference between the design supply-air temperature and the design room air temperature. Exceptions:

1. Systems that prevent reheating, recooling or mixing of heated and cooled supply air.

2. Seventy five percent of the energy for reheating is from site-recovered or site solar energy sources. 3. Zones with peak supply air quantities of 300 cfm (142 L/s) or less.

6.5.3.4 Supply-air temperature reset controls. Multiple zone HVAC systems must include controls that automatically reset the supply-air temperature in response to representative building loads, or to outdoor air temperature. The controls shall reset the supply air temperature at least 25% of the difference between the design supply-air temperature and the design room air temperature. Controls that adjust the rest based on zone humidity are allowed. Zones which are expected to experience relatively constant loads, such as electronic equipment rooms, shall be designed for the fully reset supply temperatures.

Exceptions:

a. Climate zones 1a, 2a, and 3a

b. Systems that prevent re-heating, re-cooling, or mixing of heated and cooled supply air.

c. Systems in which at least 75% of the energy for reheating (on an annual basis) is from the site recovered or site solar energy sources.

Standard 90.1-10 exempts supply air temperature reset controls in Climate Zones 1 – 3 where as the 2012 IECC does not. Standard 90.1-10 requires that zones that are expected to see constant loads be designed for the fully reset design temperature.

C403.4.6 Heat recovery for service water heating. Condenser heat recovery shall be installed for heating or reheating of service hot water provided the facility operates

24 hours a day, the total installed heat capacity of watercooled systems exceeds 6,000,000 Btu/hr (1 758 600 W) of heat rejection, and the design service water heating load exceeds 1,000,000 Btu/h (293 100 W). The required heat recovery system shall have the capacity to provide the smaller of:

1. Sixty percent of the peak heat rejection load at design conditions; or

2. The preheating required to raise the peak service hot water draw to 85°F (29°C).

Exceptions:

1. Facilities that employ condenser heat recovery for space heating or reheat purposes with a heat recovery

6.5.6.2.1 Condenser heat recovery systems shall be installed for heating or preheating of service hot water provided all of the following are true:

a. The facility operates 24 hours a day.

b. The total installed heat rejection capacity of the water- cooled systems exceeds 6,000,000 Btu/h of heat rejection.

c. The design service water heating load exceeds 1,000,000 Btu/h.

6.5.6.2.2 The required heat recovery system shall have the capacity to provide the smaller of:

a. 60% of the peak heat rejection load at design conditions, or

b. Preheat of the peak service hot water draw to 85°F. Exceptions:

a. Facilities that employ condenser heat recovery for space

A review of both documents finds them to be about the same.

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2012 IECC Standard 90.1-10 Comparative Notes

design exceeding 30 percent of the peak water-cooled condenser load at design conditions.

2. Facilities that provide 60 percent of their service water heating from site solar or site recovered energy or from other sources.

heating with a heat recovery design exceeding 30% of the peak water-cooled condenser load at design conditions.

b. Facilities that provide 60% of their service water heating from site-solar or site-recovered energy or from other sources.

C403.4.7 Hot gas bypass limitation. Cooling systems shall not use hot gas bypass or other evaporator pressure control systems unless the system is designed with multiple steps of unloading or continuous capacity modulation. The capacity of the hot gas bypass shall be limited as indicated in Table C403.4.7

Exception: Unitary packaged systems with cooling capacities not greater than 90,000 Btu/h (26 379 W).

6.5.9 Hot Gas Bypass Limitation. Cooling systems shall not