TRANE WSHP-1 Ducted Water Source Heat Pump Instructions

: June 17, 2024
: Trane

Table of Contents

TRANE WSHP-1 Ducted Water Source Heat Pump
Product Information
Product Usage Instructions
FAQ

TRANE WSHP-1 Ducted Water Source Heat Pump

TRANE-WSHP-1-Ducted-Water-Source-Heat-Pump-product

Product Information

Specifications

Heat Pump Type: Water-Source
Refrigerant: R-454B (A2L)
Occupancy Classification: Commercial
System Category: High Probability

Product Usage Instructions

System Configuration

The ducted water-source heat pump system consists of two heat pumps, WSHP-1 and WSHP-2. WSHP-1 is a 5-ton unit serving a 1445-ft2 zone, while WSHP-2 is a 3-ton unit serving an 885-ft2 zone. Both units have a ceiling height of 10 ft.

Air Distribution

The WSHPs are located in the ceiling plenum. The supply air is ducted to diffusers throughout the office space, while the return air is drawn through a ceiling-mounted grille and ducted back to the WSHPs. The supply and return ductwork is located in the ceiling plenum.

Refrigerant

Both WSHPs use R-454B (A2L) refrigerant. WSHP-1 contains a single refrigeration circuit with a total refrigerant charge of 5.8 lb, while WSHP-2 contains a single refrigeration circuit with a total refrigerant charge of 3.6 lb.

Compliance with ASHRAE Standard 15

The system falls under the high probability system category due to its use for human comfort. As a result, Section 7.6 of ASHRAE Standard 15 applies.

Effective Dispersal Volume (Veff)

In this example, the effective dispersal volumes (Veff) of the connected spaces are 14,462 ft3 for WSHP-1 and 8857 ft3 for WSHP-2. These values are used in the calculation of the EDVC (Emergency Discharge Ventilation Calculation).

EDVC Calculation

For WSHP-1, the releasable refrigerant charge (mrel = 5.8 lb) is lower than the calculated EDVC of 133 lb, as per Section 7.6.1. Therefore, WSHP-1 complies with the prescribed limit.

WSHP-2, on the other hand, has a releasable refrigerant charge (mrel) less than 4 lb, so a leak detection system is not required, according to Section 7.6.2.3.

The calculation of the EDVC for WSHP-2 is based on the floor area served (885 ft2) and the lowest point of any opening in the supply or return air duct (Height = 10 ft). Using these values and interpolating from Table 7-1 in the standard, the refrigerant charge limit (Mdef) is determined to be 31.1 lb.

FAQ

Q: What refrigerant does the water-source heat pump use?

A: The water-source heat pump uses R-454B (A2L) refrigerant.

Q: Does WSHP-2 require a leak detection system?

A: No, WSHP-2 does not require a leak detection system as its releasable refrigerant charge is less than 4 lb.

Q: What is the EDVC for WSHP-1?

A: The calculated EDVC for WSHP-1 is 133 lb, which is higher than its releasable refrigerant charge of 5.8 lb, ensuring compliance with the prescribed limit.

Ducted Water-Source Heat Pump

The following abridged material is from Trane application manual APP- APM001-EN, Refrigeration Systems and Machinery Rooms: Application Considerations for Compliance with ASHRAE® Standard 15-2022. It is strongly recommended that any user of this document also reviews the source material for additional clarifications, givens, and commentary.
A water-source heat pump is classified by Standard 15 as a “high-probability” system, since leaked refrigerant has a high probability of entering the occupied space. When designing a high-probability system, the occupied space must be of sufficient “volume” to safely disperse and dilute any leaked refrigerant. Dilution is the solution! The maximum allowable refrigerant charge, known as the Effective Dispersal Volume Charge (EDVC), is calculated using the volume available to disperse the leaked refrigerant, and depends on the refrigerant’s safety group classification.
Standard 15 may provide more than one approach for complying with the EDVC. The designer may use one or a combination of several of these approaches. For the purposes of brevity, it is not possible to discuss all possible approaches, so this document only focuses on the simplest approach. Refer to Trane application manual APP-APM001-EN for additional approaches.
Because ASHRAE Standard 15 is under continuous maintenance, the requirements can change frequently. This document is based on the 2022 published version. Refer to the ASHRAE web site for the most current version of the standard, including any published addenda and errata.

Example: Ducted Water-Source Heat Pump System Serving a “Commercial” Occupancy with an A2L Refrigerant
Given: A water-source heat pump (WSHP) consists of two heat pumps, each serving a zone on a commercial office building. WSHP-1 is a 5-ton unit that serves a 1445-ft2 zone, with a 10-ft ceiling height. WSHP-2 is a 3-ton unit that serves an 885-ft2 zone, with a 10-ft ceiling height.

Both WSHPs consist of a single refrigeration circuit with R-454B (A2L) refrigerant.
The horizontal-style WSHPs are located in the ceiling plenum. Supply air is ducted to diffusers located throughout the office space. Return air is drawn through a ceiling-mounted grille and ducted back the WSHP. The supply and return ductwork is located in the ceiling plenum.
Per Standard 15, the occupancy classification is “commercial” (Focc = 1.0) and this system is categorized as a “high probability” system

Solution (A2L refrigerant)

This is an example of “connected spaces” via a ducted air distribution system (per Section 7.2.3.3). When calculating the effective dispersal volume (Veff) of the connected spaces in this example, include the following:

The volume of the office space: 14,450 ft3 for WSHP-1 and 8850 ft3 for WSHP-2.
The volume of the supply and return ductwork: 12 ft3 for WSHP-1 and 7 ft3 for WSHP-2. (Note that this volume would be ignored if the ductwork is routed through a ceiling plenum that was used as part of the return-air path.)

…but exclude the following:

The volume of the interstitial ceiling plenum is not included in this example, since it is not part of the return-air path.

For this example, the effective dispersal volumes (Veff) of the connected spaces are 14,462 ft3 for WSHP-1 and 8857 ft3 for WSHP-2.

WSHP-1

WSHP-1 consists of a single, 5-ton refrigeration circuit containing 5.8 lb of R-454B refrigerant, while WSHP-2 consists of a single, 3-ton circuit containing 3.6 lb of R-454B. Per Section 7.3.4.1, the releasable refrigerant charges (mrel) are the entire charges of 5.8 lb and 3.6 lb, respectively.
Standard 34 lists R-454B as Group A2L refrigerant with an LFL of 18.5 lb/1000 ft3 or 0.0185 lb/ft3.
Since these are high-probability systems used for human comfort, the use of a Group A2L refrigerant means that the requirements of Section 7.6 apply.
WSHP-1 is ducted, and mrel is greater than 4 lb, so Section 7.6.2.3 requires that it be equipped with a leak detection system that is listed with the equipment. WSHP-1 in this example includes two refrigerant detectors– both of which comply with the requirements of Section 7.6.2.4–to initiate air circulation in the event that a leak is detected. One of the detectors is located in the evaporator section and the other in the compressor section. If a leak is detected in either location, the evaporator fan is activated to disperse any leaked refrigerant. This example WSHP contains a method to allow a leak in the compressor section to be circulated by the supply fan and dispersed throughout the same volume.
Since WSHP-1 uses air circulation to disperse any leaked refrigerant, then per Section 7.6.1.1, the EDVC is calculated to be 133 lb:
EDVC = 0.0185 lb/ft3 × 14,462 ft3 × 0.5 × 1.0 = 133 lb
For WSHP-1 in this example, the releasable refrigerant charge (mrel = 5.8 lb) is lower than the EDVC, so this system complies with the limit prescribed by Section 7.6.1.

WSHP-2

WSHP-2 is also ducted, but mrel is less than 4 lb, so Section 7.6.2.3 does not require a leak detection system.
Since WSHP-2 does not use air circulation to disperse any leaked refrigerant, then Section 7.6.1.2 is used to calculate the EDVC:
The floor area served by WSHP-2 is 885 ft2 and the lowest point of any opening in the supply or return air duct (“Height”) is 10 ft. Using these values, and interpolating from Table 7-1 in the standard, the refrigerant charge limit, Mdef, is 31.1 lb.
Applying the correction factor for R-454B from Table 7-3, the EDVC is calculated to be 30 lb:
EDVC = 31.1 lb × 0.97 × 1.0 = 30 lb
For WSHP-2 in this example, the releasable refrigerant charge (mrel = 3.6 lb) is lower than the EDVC, so this system complies with the limit prescribed by Section 7.6.1.
Refer to the Trane application manual APP-APM001*-EN for more details.

Systems with air circulation

If the system has either continuous air circulation (except during short periods for maintenance or service) or air circulation that is initiated by a refrigerant detector that complies with Section 7.6.2.4, the EDVC is calculated as follows (per Section 7.6.1.1):

EDVC = LFL × Veff × CF × Focc
where,
EDVC = effective dispersal volume charge, lb (kg)

Veff = effective dispersal volume per Sections 7.2.1 through 7.2.3, ft3 (m3)

LFL = lower flammability limit of the refrigerant, lb/ft3 (kg/m3)

CF = concentration factor = 0.5 Focc = occupancy adjustment factor (0.5 for institutional; 1.0 for all others)

Note that the values tabulated in ASHRAE Standard 34 are in units of lb/1000 ft3 and g/m3, so be sure to convert to the correct units when using this formula.
When air circulation is used to disperse leaked refrigerant, the UL product safety standard (UL 60335-2-40) prescribes the minimum circulation air flow rate.

Other refrigeration systems

If the system does not meet the air circulation requirements of Section 7.6.1.1, then the EDVC is calculated as follows (per Section 7.6.1.2):

EDVC = Mdef × FLFL × Focc
where,
EDVC = effective dispersal volume charge, lb (kg) Mdef = refrigerant charge limi from Table 7-1 (lb) or Table 7-2 (kg) FLFL = LFL conversion factor from Table 7-3 Focc = occupancy adjustment factor (0.5 for institutional; 1.0 for all others)

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WSHP-PRB003A-EN December 2023