Mammoth 800 to 5500 CFM: Dedicated Outdoor Air System with Enthalpy Wheels (VHC) User Manual

Page 39

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MAMM-VHC-IOM-1A (JANUARY 2013)

Functional Descriptions

Head Pressure Control

A three-way modulating head pressure control valve is re-

quired to maintain stable operation of the refrigeration sys-

tems when operated on ground loop water systems when

the design water temperature is below 65°F in the cooling

mode. A refrigerant pressure sensor on the compressor

discharge is used to modulate the water flow to the con-

denser using a 2 to 10 VDC signal to artificially keep the

compressor discharge pressure at a high enough operat-

ing condition to prevent the low pressure refrigerant switch

from tripping.
The three-way modulating head pressure control valve

consists of a 24 VAC NEMA 1 or 2 modulating actua-

tor with a temperature rating of −22°F to 122°F [−30°C

to 50°C], nickel plated forged brass valve with stainless

steel ball, stem and replaceable valve cartridge assembly

which is an option and must be externally field mounted.

For outdoor applications a NEMA 4x rated actuator must

be installed. The hydronic valves are intended for use in a

normal indoor/outdoor environment for hot or cold water

or glycol solutions to 60% concentration with a medium

temperature rating of 0°F to 212°F [−18°C to 100°C]. The

valve and actuator are preassembled for 100% flow to the

coil with minimum of 2 VDC signal. The refrigerant pres-

sure sensor is internally factory mounted, prewired and

programmed for the DDC to control the three-way valve. A

6 foot coiled wiring harness is factory supplied with the unit,

located in the compressor compartment for field extension

and wiring to the actuator.
See Table K2 for three-way valve sizing and performance

data. Dimensions, technical and installation data follow.

See the wiring schematic for connection and the VHC-36,

42 and 50 DDC Control Package Manual for sequencing

information.

Water Shut-off

A two-way motorized on/off water shut-off valve is required

to isolate water flowing through both the economizer coil (if

equipped) and water-to-refrigerant condenser for conser-

vation when the unit is off. The water shut-off valve must

be placed upstream of the economizer coil and three-way

economizer control valve and the three-way modulating

head pressure control valve (if equipped). The motorized

water valve must open 90 seconds prior to compressor

start-up and remain open five seconds after the compres-

sor is shut off.
The two-way motorized water shut-off valve is an acces-

sory item and consists of a 24 VAC NEMA 1 or 2 on/off ac-

tuator with a temperature rating of −22°F to 122° F [−30°C

to 50°C], nickel plated forged brass valve and replaceable

valve cartridge assembly which is an accessory and must

be externally field mounted. For outdoor applications a

Appendix K: Water Line Field Mounted Options and Accessories

IMPORTANT

• Water source heat pump external water supply and

return piping shall be in accordance with National

and Local Codes. Line sizing, pressure limiting

devices, backflow preventers, strainers, valves,

flow temperature and pressure measuring, freeze

protection and all other safety or control piping

requirements for system operation are the sole re-

sponsibility of the Installing Contractor and/or Design

Engineer.

• Some external piping components and control inter-

locks are offered as an option or accessory for partly

field and factory installation and are summarized in

Table K1. A detailed functional description follows.

• On open loop systems, a field supplied and installed

water strainer (16–20 mesh minimum) is recom-

mended in the water inlet or supply line to the unit to

eliminate contaminants and must be used for 14, 16

and 21 ton dual circuit WSHP units which utilize a

brazed plate heat exchanger condenser.

• Air vents must be field installed on the high side

of the water supply or inlet line to discharge the

noncondensable air in order to avoid unexpected

high head pressure and poor cooling/heating perfor-

mance.

• Manual shut-off valves in supply and return water

lines are recommended to be field installed for isola-

tion and service.

• A circuit balancing valve with pressure and tempera-

ture gauge connections is recommended to be field

supplied and installed for balancing and service. The

water supply must be sized for the minimum flow as

indicated on the submittals.

• Prior to connection of condensing water supply, ver-

ify water pressure is less than the maximum pres-

sure for components in the water line. To prevent

injury or death due to instantaneous release of high

pressure water, relief valves should be field supplied

and installed in system water piping.

• Maximum working pressure, pressure drop or C

factors for condenser and optional or accessory

components are given in tables below.

Table K1: WSHP Water Line Option or Accessory

Function Field Installed

Factory Installed

Head

pressure

control

Three-way water

control valve with

modulating actuator

Head pressure control

DDC program logic

Refrigerant pressure

transducer

Water

shut-off

Two-way water shut-off

valve with on/off actua-

tor

Water on/off control

DDC program logic

Freeze

protection Water flow switch

Unit on/off control DDC

program logic

Water outlet tempera-

ture sensor

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