23 84 00 HUMIDITY CONTROL EQUIPMENT

.01 Design Requirements

1. Application
   1. Section 23 84 00 of this Standard is intended to cover special circumstances where the occupancy or a process requires humidification or dehumidification outside of the default indoor design criteria defined in Section 23 00 00. 
   2. Centralized or terminal humidification shall not be provided for ordinary space conditioning purposes.

      1. For reference to designer: Humidification systems have the potential to cause considerable damage to building envelopes and contribute to indoor air quality issues. OPP requires specific documentation and approvals to avoid the mis-application of these systems. The successful implementation of a humidification system requires a firm understanding of the environmental requirements, operational capabilities of the equipment, and coordination with other building systems.

   3. Humidification is only permissible to maintain specific environmental conditions for a special equipment or process. These special purposes shall be identified by the Designer during the schematic design phase and are subject to review and approval by OPP.

      1. The Designer shall document on the design drawings the required temperature/humidity ranges, operational tolerances, and location of all humidified spaces/equipment.

2. Allocation

   1. To preserve the integrity of building enclosures and avoid indoor condensation, the Designer shall prioritize allocating humidified spaces to locations without exterior exposure.

   2. Where exterior exposure in humidified spaces is unavoidable the Designer shall perform the following building envelope analysis, which is subject to review and approval by OPP.

      1. Calculate the interior surface temperatures at Design winter conditions.

      2. Establish the indoor air dewpoint range according to the required temperature and humidity targets.

      3. If condensation were to occur, identify the risks to the occupancy and/or process.

      4. Evaluate the effects of moisture migration through the building envelope materials

   3. Humidified spaces shall be provided with vapor barrier to manage moisture migration between adjacent spaces with different levels of humidification.

3. System Selection

   1. Designer shall calculate humidification and dehumidification loads based on indoor design requirements, climatic conditions, and moisture gain due to internal loads, infiltration, and envelope moisture migration. Calculations shall be submitted to OPP for review and approval.

   2. Humidification:

      1. All humidification loads shall be calculated based on ASHRAE Climatic Design Information for the “99.6% Heating DB” condition.

   3. Dehumidification:

      1. All dehumidification loads shall be calculated based on ASHRAE Climatic Design Information for the “0.4% Dehumidification” condition.

      2. Refer to Table 238400.01 - Dehumidification system selection matrix

4. Recognized industry resources

   1. The following chapters from ASHRAE HVAC Systems and Equipment Handbook

      1. Humidifiers

      2. Air-Cooling and Dehumidifying Coils

      3. Desiccant Dehumidification and Pressure-Drying Equipment

      4. Mechanical Dehumidifiers and Related Components

   2. The Dehumidification Handbook – Third Edition (Munters)

   3. Whole Building Design Guide (https://www.wbdg.org/)

      1. Building Envelope Design Guide

.02 Humidifiers

1. Heating source selection:
   1. Steam is the preferred source for direct-injection humidifiers and indirect steam generators. The only exception is where connection to the campus hot water heating system is anticipated. The Designer shall consult with OPP Engineering Services to determine where steam should be avoided in a particular building.

   2. Where campus steam is unavailable, natural gas is the second preference. Electricity shall be the heating source of last resort.

2. Heated pan, centrifugal, ultrasonic, and wetted-media type humidifiers are prohibited.

3. All isothermal humidifiers require insulated dispersion tubes. This insulation shall be factory applied, non-fibrous/closed-cell, UV light resistant, and have a minimum R-value of 0.5. Steam-jacketed manifolds are prohibited due to the operational limitations from the associated sensible heat gain.

4. Atomizing humidifiers

   1. Pressurized water-humidifiers are the only permissible type of atomizing humidifier.

   2. Atomizing humidifiers shall not be used for terminal humidification.

   3. For reference to Designer: Adiabatic-type humidifiers (atomizing) require additional heating coil capacity to compensate for the drop in air temperature associated with the heat of vaporization. This can limit the operational flexibility of air systems. The applicability of isothermal versus adiabatic humidifiers shall be reviewed on a case-by-case basis.

5. Direct steam injection humidifiers

   1. Direct injection humidifiers shall be provided with a motorized isolation valve and a steam control valve.

6. Self-contained humidifiers

   1. Self-contained (indirect) humidifiers shall utilize building steam or natural gas as the energy source where available.

   2. Immersed electrode canister type shall be used for non-critical or temporary applications only.

   3. Resistive electric type shall be used for most applications where the energy source is electric.

7. All humidifiers requiring make-up water shall be provided with water treatment systems – no exceptions.

   1. Humidifiers fed from water softeners shall be provided with an automatic flushing and dilution cycle.

   2. Humidifier equipment and piping fed with demineralized water (RO/DI) must withstand the corrosive effects of this water.

8. Follow manufacturer’s guidelines for locating duct mounted distribution manifolds.

9. Provide access panel with a glass vision panel on downstream side of duct mounted manifolds.

10. Duct mounted humidifiers shall be installed in a section of welded 304 stainless steel ductwork with a minimum length resulting from 1 foot upstream plus three times the absorption distance downstream of the humidifier. The humidifier section shall have a double-sloped bottom with drain connection.

.03 Dehumidifiers

1. Three main types of dehumidifiers are typically used for controlling humidity levels. The Designer shall utilize the existing campus utilities to the greatest extent possible given the dehumidification application and its level of criticality.

   1. Cooling/Reheat systems are the preferred method of dehumidification as they are conventional and cost effective.

   2. Desiccant systems

   3. Small packaged heat pump dehumidifiers are typically limited to temporary, portable systems and are not intended for permanent installation. If used, these units shall be arranged so condensate is piped to the sanitary system.