Nordic ATWC Series Manual

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Maritime Geothermal Ltd.
P.O. Box 2555, 170 Plantation Road
Petitcodiac, NB E4Z 6H4
[phone]
ATWC-Series
High Temperature Air to Water Heat Pump
R134a with Switchable R410a Cascade Mode
Model Sizes 45-100
Space Heating or Dedicated Domestic Hot Water Options
[email protected]
www.nordicghp.com
002536MAN-00
PRELIMINARY
24-Sep-2021
Installation and Service Manual

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ATWC—65—HAC—C—1D—P—xx
Series:
ATWC = high temperature cascade
air to water heat pump
Nominal Size:
45 = nominal 3 ton
55 = nominal 4 ton
65 = nominal 5 ton
75 = nominal 6 ton
80 = nominal 6.5 ton
100 = nominal 8 ton
Functions:
H = Heating
AC = Active Cooling
Refrigerant:
C = cascade R410a/R134a
Voltage Code:
1 = 230-1-60 VAC
2 = 208-3-60 VAC
4 = 460-3-60 VAC
6 = 220-1-50 VAC
7 = 380-3-50 VAC
Indoor Loop Exchanger:
P = brazed plate (single wall)
D = brazed plate (double
wall for DHW)
Revision:
01, 02 etc.
Compressor:
D = dual scroll
WARNING: Ensure all access panels are in place and properly secured before applying power to the unit.
Failure to do so may cause electrical shock.
WARNING: Before performing service or maintenance on the heat pump system, ensure all power sources
are DISCONNECTED. Electrical shock can cause serious personal injury or death.
WARNING: Heat pump systems contain refrigerant under high pressure and as such can be hazardous to
work on. Only qualified service personnel should install, repair, or service the heat pump.
CAUTION: Safety glasses and work gloves should be worn at all times whenever a heat pump is serviced.
A fire extinguisher and proper ventilation should be present whenever brazing is performed.
CAUTION: Venting refrigerant to atmosphere is illegal. A proper refrigerant recovery system must be
employed whenever repairs require removal of refrigerant from the heat pump.
SAFETY PRECAUTIONS
Model Nomenclature
ACEC—65—C—1—KDE—xx
Series:
ACEC = All weather Condenser / Evaporator
Cascade (air source outdoor unit)
Nominal Size:
45 = for ATWC-45
55 = for ATWC-55
65 = for ATWC-65
75 = for ATWC-75
80 = for ATWC-80
100 = for ATWC-100
Voltage Code:
1 = 208/230-1-60
Air Coil:
S = Standard
K = Coated
Fan Type:
D = Direct Drive
Fan Motor:
E = ECM (Variable Speed)
Revision:
01, 02 etc.
Refrigerant:
C = cascade R410a/R134a

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APPLICATION TABLE - INDOOR UNIT
SIZE FUNCTION REFRIGERANT VOLTAGE COMPRESSOR INDOOR
COIL
REVISIONS
ATWC-45 H A C C
1
2
4
6
7
D P
D 00
ATWC-55 H A C C
1
2
4
6
7
D P
D 00
ATWC-65 H A C C
1
2
6
7
D P
D 00
ATWC-75 H A C C
1
2
6
7
D P
D 00
ATWC-100 H A C C 2
7 D P
D 00
This manual applies only to the models and revisions listed in this table.
ATWC-80 H A C C
1
2
6
7
D P
D 00
Maritime Geothermal Ltd. has a continuous improvement policy and reserves the right to modify specification
data at any time without prior notice.
APPLICATION TABLE - FIRMWARE AND PC APP
Firmware Version* Associated PC APP Version
MGT GEN2 Bootload Firmware V4.00+ MGT GEN2 PC APP V2.20+
APPLICATION TABLE - OUTDOOR UNIT
MODEL REFRIGERANT VOLTAGE AIR COIL BLOWER TYPE BLOWER MOTOR REVISIONS
ACEC-45 C 1 K D E 00
ACEC-55 C 1 K D E 00
ACEC-65 C 1 K D E 00
ACEC-100 C 1 K D E 00
This manual applies only to the models and revisions listed in this table.
ACEC-75 C 1 K D E 00
ACEC-80 C 1 K D E 00

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Table of Contents
Tables & Documents ........................................................ 5
ATWC System Description .............................................. 6
General Overview ................................................................... 6
1. Heating Mode ..................................................................... 6
Auxiliary Heat .................................................................... 6
Defrost Operation.............................................................. 6
2. Cooling Mode ...................................................................... 6
One or Two Buffer Tanks? .............................................. 7
Single Buffer Tank Systems .................................................... 7
Dual Buffer Tank Systems ...................................................... 7
ATWC Sizing ....................................................................... 8
Air Source Heat Pumps .......................................................... 8
Heat Pump Sizing for Space Heating / Cooling ....................... 8
Auxiliary Heat Sizing ............................................................... 8
Installation Basics ............................................................. 9
Sample Bill of Materials .......................................................... 9
Unpacking the unit .................................................................. 9
Indoor Unit Placement ............................................................ 9
Outdoor Unit Placement ........................................................ 10
Line Sets ............................................................................... 10
Outdoor Unit Mounting Height .............................................. 10
Outdoor Fan Speed Reduction ............................................. 10
Average Max. Snow Depth Map - Canada ............................ 11
Wiring ................................................................................. 12
Indoor Unit Power Supply Connections ................................ 12
Outdoor Unit: Power Connections ........................................ 12
Indoor Loop Circulator Pump Wiring ..................................... 12
Control Transformer .............................................................. 12
BACnet Connections ............................................................ 13
Setpoint Control Connections ................................................ 13
Setpoint Control: Aux. Connections ....................................... 13
Outdoor Unit: Signal Connections ......................................... 14
Aquastat Connections (Optional) .......................................... 14
Disable Switch (field installed) ............................................... 14
Defrost Indicator (field installed) ............................................ 14
002543CDG - Typical ATWC/ATW2 Series Wiring ............... 15
002375QSS - AltSource Tanks: Getting Started ................... 16
002067CDG - Typ. Heating Only Zone Wiring (Setpoint) ...... 17
002068CDG - Typ. Htg/Cooling Zone Wiring (Setpoint) ........ 18
Piping ................................................................................. 19
Number of Tanks .................................................................. 19
Indoor Loop Water Lines ........................................................ 19
002540PDG - Piping Connections - Space Heating/Cooling . 20
002366PDG - Recommended Buffer Tank Piping ................. 21
002528PDG - Buffer Tank Piping - Multiple Units .................. 22
002252PDG - 2 Tank Piping with a Reversing Heat Pump .... 23
002527PDG - 2 Tank Piping w/Multiple Rev. Heat Pumps .... 24
002367PDG - Auxiliary Boiler Piping ..................................... 25
000530PDG - Typical Zone Types ......................................... 26
002541PDG - Piping Connections - Direct DHW Heating ...... 27
002545PDG - Tank Piping for Direct DHW Heating ............... 28
Outdoor Unit Line Sets .................................................. 29
Line Set Interconnect Tubing ................................................ 29
Indoor Unit Connections ........................................................ 29
Outdoor Unit Connections ...................................................... 29
Oil Traps ............................................................................... 29
Filter-Dryer ............................................................................ 29
Pipe Insulation ...................................................................... 30
Silver Soldering Line Sets ..................................................... 30
Pressure Testing ................................................................... 30
Vacuuming the System .......................................................... 30
Charging the System ............................................................. 30
002544CDG - Typical ATWC Line Set Connections .............. 31
Operation ........................................................................... 32
1. BACnet Control ................................................................. 32
2. Signals / Hardwired Control .............................................. 32
3. Setpoint Control ................................................................ 32
Setpoint Control Method 1 - Indoor Loop (ICR), One Tank .... 32
Typical ATWC-Series Setpoints ......................................... 33
Top Up S1 Function ........................................................... 33
Summer Setback ................................................................ 33
Hydronic Auxiliary in Defrost .............................................. 33
Outdoor Reset .................................................................... 34
Setpoint Control Method 2 - Indoor Loop (ICR), 2 Tanks ....... 34
Setpoint Control Method 3 - External HTS/CTS, One Tank .. 35
Setpoint Control Method 4 - External HTS/CTS, 2 Tanks ..... 36
PC Application (PC App) ............................................... 37
LCD Interface & Menus .................................................. 49
BACnet Interface .............................................................. 51
Startup Procedure ........................................................... 55
Pre-start Inspection ............................................................... 55
Unit Startup ........................................................................... 56
Startup Record ...................................................................... 57
Routine Maintenance ...................................................... 58
Troubleshooting Guide .................................................. 59
Repair Procedures .......................................................... 68
Pumpdown Procedure .......................................................... 68
General Repair Procedure .................................................... 68
Vacuuming & Charging Procedure ....................................... 68
Compressor Replacement Procedure ................................... 69
Control Board Replacement Procedure ................................ 70
LCD Interface (Display) Board Replacement Procedure ....... 71
Model Specific Information ........................................... 72
Shipping Information ............................................................. 72
Refrigerant Charge ............................................................... 72
Indoor Loop Flow Rates ........................................................ 72
Operating Temperature Limits .............................................. 72
Sound Levels (dBA) .............................................................. 72
Pressure Drop Data ............................................................... 73
Performance Tables .............................................................. 74
Electrical Specifications ........................................................ 80
Wiring Diagram (208/230-1-60) ............................................ 81
Electrical Box Layout (208/230-1-60) .................................... 82
Wiring Diagram (208-3-60) ................................................... 83
Electrical Box Layout (208-3-60) ........................................... 84
Wiring Diagram (460-3-60) .................................................... 85
Electrical Box Layout (460-3-60) ........................................... 86
ACEC-45/55 Wiring Diagram ................................................. 87
ACEC-65/75/80/100 Wiring Diagram ..................................... 88
ATWC Refrigeration Circuit - Cascade Heating Mode ........... 89
ATWC Refrigeration Circuit - Warm Weather Heating Mode . 90
ATWC Refrigeration Circuit - Defrost/Cooling Mode .............. 91
Dimensions: ATWC-45/55 ..................................................... 92
Dimensions: ATWC-65 .......................................................... 94
Dimensions: ATWC-75/80/100 .............................................. 96
Appendix A: Control Board Description ..................... 98
Appendix B: USB Driver Installation ......................... 102
Appendix C: PC App Installation ............................... 103
Appendix D: Updating Firmware ................................ 104
Warranty .......................................................................... 106

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Tables & Documents
Tables
Documents
Table 1 - Heat Pump Size vs. Heated Area .............................................................................................. 8
Table 2 - Auxiliary Heat Sizing ................................................................................................................ 8
Table 3 - Power Supply Connections .................................................................................................... 12
Table 4 - Outdoor Unit Power Supply Connections ............................................................................... 12
Table 5 - Indoor Loop Circulator Connections ....................................................................................... 12
Table 6 - Control Transformer ............................................................................................................... 12
Table 7 - BACnet Connections .............................................................................................................. 13
Table 8 - Setpoint Control Connections ................................................................................................. 13
Table 9 - Setpoint Control: Aux. Connections ........................................................................................ 13
Table 10 - Outdoor Unit Signal Connections ......................................................................................... 14
Table 11 - Aquastat (Signals Control) Connections ............................................................................... 14
Table 12 - Buffer Tank Size ................................................................................................................... 19
Table 13 - Line Set Sizing ..................................................................................................................... 29
Table 14a - 3-way Service Valve Tooling .............................................................................................. 29
Table 14b - 3-way Service Valve Torques ............................................................................................. 29
Table 15 - Extra Charge for 3/8” / 3/4” Line Sets ................................................................................... 30
Table 16 - Extra Charge for 1/2” / 7/8” Line Sets .................................................................................... 30
Table 17 - Typical ATWC-Series Setpoints ........................................................................................... 33
Table 18 - Maximum Output Temperature ............................................................................................. 34
Table 19 - BACnet Objects - Control Signals (Read/Write) .................................................................... 51
Table 20 - BACnet Objects - Operation Mode Description (Read Only) ................................................. 51
Table 21 - BACnet Objects - Data (Read Only) ...................................................................................... 52
Table 22 - BACnet Objects - Alarm Descriptions (Read Only) ............................................................... 53
Table 23 - BACnet Objects - Fault Descriptions (Read Only) ................................................................. 54
Table 24 - Shipping Information (Indoor Unit) ........................................................................................ 72
Table 25 - Shipping Information (Outdoor Unit) ..................................................................................... 72
Table 26 - Refrigerant Charge ............................................................................................................... 72
Table 27 - Indoor Loop Flow Rates ....................................................................................................... 72
Table 28 - Operating Temperature Limits .............................................................................................. 72
Table 29 - Outdoor Unit Sound Levels (dBA) ........................................................................................ 72
Table 30 - Indoor Unit Sound Levels (dBA) ........................................................................................... 72
Table 31 - Loop Pressure Drop Data ..................................................................................................... 73
Table 32 - ATWC-Series Electrical Specifications ................................................................................. 80
Table A1 - Control Board Connector Descriptions (Top) ........................................................................ 9 9
Table A2 - Control Board Connector Descriptions (Left Side) .............................................................. 99
Table A3 - Control Board Connector Descriptions (Bottom) ................................................................ 100
Table A4 - Control Board Connector Descriptions (Right Side) ........................................................... 101
002543CDG - Typical ATWC/ATW2 Outdoor Unit, Aux. Heat, & Indoor Circulator Wiring ................... 15
002375QSS - AltSource Tanks: Getting Started ................................................................................... 16
002067CDG - Typical Zone and Auxiliary Wiring with GEN2 Setpoint Control (Heating Only) .............. 17
002068CDG - Typical Zone and Auxiliary Wiring with GEN2 Setpoint Control (Heating & Cooling) ..... 18
002540PDG - Typical ATWC Piping Connections - High Temperature Space Heating/Cooling ........... 20
002366PDG - Recommended Hydronic Buffer Tank Piping .................................................................. 21
002528PDG - Buffer Tank Piping - Multiple Units .................................................................................. 22
002252PDG - Two Tank Piping with a Reversing Heat Pump ............................................................... 23
002527PDG - Two Tank Piping with Multiple Reversing Heat Pumps .................................................... 24
002367PDG - Auxiliary Boiler Piping ..................................................................................................... 25
000530PDG - Typical Zone Types for Hydronic Applications ................................................................. 26
002541PDG - Typical ATWC Piping Connections - Direct DHW Heating with Double Wall Cond. ....... 27
002545PDG - Tank Piping for Direct DHW Heating for Heat Pumps with Double Wall Condenser ....... 28
002544PDG - Typical ATWC to Outdoor Unit Line Set Connections ...................................................... 31
002491SCH - ATWC-**-HAC-C-1D-* Schematic Diagram ..................................................................... 81
002537ELB - ATWC-**-HAC-C-1D-* Electrical Box Diagram ................................................................. 82
002492SCH - ATWC-**-HAC-C-2D-* Schematic Diagram ..................................................................... 83
002538ELB - ATWC-**-HAC-C-2D-* Electrical Box Diagram ................................................................. 84
002493SCH - ATWC-**-HAC-C-4D-* Schematic Diagram ..................................................................... 85
002539ELB - ATWC-**-HAC-C-4D-* Electrical Box Diagram ................................................................. 86
002441SCH - ACEC 45/55 Schematic Diagram .................................................................................... 8 7
002488SCH - ACEC 65-100 Schematic Diagram .................................................................................. 90
002454RCD - ATWC-Series Refrigeration Circuit - Cascade Heating Mode ......................................... 89
002455RCD - ATWC-Series Refrigeration Circuit - Warm Weather Heating Mode ............................... 90
002456RCD - ATWC-Series Refrigeration Circuit - Defrost/Cooling Mode ........................................... 91

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General Overview
The NORDIC ATWC-Series heat pump is a high tem-
perature switchable cascade air source heat pump that can
heat water to a higher temperature than a standard hydronic
heat pump, or cool water for hydronic cooling applications. Ap-
plications include heating through higher-temperature radiators
or hydronic baseboards, heating domestic hot water to its final
temperature with the optional built-in double wall condenser,
and heating and cooling through hydronic air handlers. Models
range from 3 to 8 tons in size.
Being an air source heat pump, it does not require a
ground loop, instead using an outdoor fan unit to exchange heat
with the outdoor air. Unlike most air source outdoor units on the
market, this outdoor unit contains only an air coil, ECM hub mo-
tor fans, expansion valves (EEVs), and outdoor temperature
sensor. The remaining components, including the compressors
and control board, are contained in the indoor unit. This has
several advantages: minimal installation and service work must
be performed outdoors, important components are in the condi-
tioned space for longevity, antifreeze is not required in the hy-
dronic loop, and no electric compressor heater is required.
Cascade heat pumps like the ATWC use two refriger-
ant circuits. In heating mode, heat is extracted from the outdoor
air by the R410a circuit, and passes that heat on to the R134a
circuit which puts that heat in the indoor water loop. With each
circuit only doing part of the temperature lift, a higher indoor
water temperature is possible. However, normally this means
that the COP is not as good as a standard heat pump when the
temperature lift is low (i.e. when it is not very cold outside). The
ATWC overcomes this problem by switching into non-cascade
mode, only using the R134a circuit, during periods of mild out-
door temperature. Cooling/defrost mode does not have a high
temperature requirement, so always uses non-cascade mode.
The heat pump will be set up to heat or cool water in a
buffer tank to a user-selectable setpoint temperature; when a
zone thermostat requires heat or cooling, it will receive water
flow from that tank by opening a zone valve or starting a zone
pump. (Two buffer tanks, heated and chilled, may be used in-
stead where heating and cooling demands may occur simulta-
neously or close together; see next chapter.) Water tempera-
ture control is usually performed by a built-in routine that main-
tains the buffer tank temperature without external sensors
(’Setpoint Control’). Optionally, BACnet, external tank sensors,
or an external aquastat or controller can be used.
Single stage scroll compressors for both circuits and
brazed plate heat exchangers are standard. The cabinets are
powder coated galvanized sheet metal. Control is overseen by
the Nordic GEN2 programmable control board, which has many
advanced features like laptop connectivity via the free PC App
software, data logging & graphing, and real time readout from
electronic temperature & pressure sensors.
Unlike many other NORDIC heat pumps, there is no DHW
desuperheater on the ATWC series. Instead there is the option
for a double wall condenser for dedicated DHW heating.
Note that there is a significant electrical service require-
ment for ATWC series, with its 2 compressors. 3-phase power
is recommended, and required for size ATWC-100. An electri-
cian should be consulted during the planning phase of any pro-
ject to verify the building’s electrical panel capacity.
1. Heating Mode
In heating mode, heat is extracted from the outdoor air and
transferred to water in the buffer tank. This causes the air coil
to eventually frost up to the point that a defrost cycle is required;
ATWC System Description
refer to the Defrost Operation section below.
If the outdoor temperature is above 34°F(1°C), the outdoor
unit fan starts and stops when the heat pump starts and stops.
If the temperature is below 34°F(1°C), the outdoor fan will re-
main on at a very slow speed when the heat pump is off to mini-
mize the chance of a fan freeze up, and to prevent snow from
entering the unit. The outdoor fan will slowly ramp up to the
required speed upon start.
Auxiliary Heat
Any air source heat pump will need auxiliary heat; see
Sizing section. This can be almost any heating device, but
the most convenient is electric elements in the buffer tank con-
trolled by the heat pump’s stage 2 temperature control (stage 1
being the compressors). The heat pump will turn off and only
the auxiliary heating system will operate if the outdoor tempera-
ture drops below -7°F (-22°C).
Defrost Operation
The heat pump has an advanced defrost control algorithm,
using outdoor temperature and suction pressure to determine
when a defrost cycle should occur and how long it should be.
Precise fan control allows the defrost heat to rise quickly and
then be maintained at a setpoint for quick defrosting.
The outdoor unit has a unique physical arrangement for
combatting the ice build up that is a common problem with air
source heat pumps. The air coil is installed on a 15° angle and
the area below the coil is open (no drip tray). The angle causes
the melting frost/snow to run down the back of the coil to a sin-
gle point of runoff rather than along the entire bottom side of the
coil. It is not possible for runoff to remain between coil pipes
and re-freeze between them, which a common cause of air coil
failure in air source heat pumps.
2. Cooling Mode
In cooling mode, heat is extracted from the buffer tank and
rejected to the outdoor air. There is no defrost cycle in cooling
mode.
The outdoor fan is controlled based on the discharge pres-
sure and will slowly ramp up to the required speed when the
system starts. During operation, the fan speed will automatical-
ly adjust up or down to in order to maintain the discharge pres-
sure setpoint value.
* See
following
chapters for
annotated
diagrams

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One or Two Buffer Tanks?
Single Buffer Tank Systems
By far, this is how most systems are config-
ured. The heat pump either heats water in the
buffer (or DHW) tank for use during heating sea-
son, or chills water in the buffer tank for zone use
during cooling season. Note that a single tank is
always all that is required for heating-only sys-
tems that don’t do cooling.
Advantages Drawbacks
Simplest piping and control. Seasonal switchover from heating to cooling required, either
automatically through a zone controller or via a manual switch.
Takes the least amount of mechanical room space.
Lower equipment cost than a 2-tank system.
Works well for heating and cooling using 2-pipe air handlers
(and in-floor heating).
For space heating/cooling heat pumps, dedicated DHW preheat-
ing is not possible in summer due to no hot tank being available.
Is the go-to option for heating-only or dedicated domestic hot
water (DHW) heating systems.
Simultaneous heating and cooling is not possible; heating and
cooling in close proximity is not practical.
Dual Buffer Tank Systems
There are some situations in which it
is advantageous to use two tanks, one
always heated and one always chilled.
The heat pump has a built in routine to
automatically maintain both the hot and
cold tank temperatures.
In this system, hot and cold water
are available for use at any time. In the
setup described here, the heat pump
switches back and forth using a 3-way
valve to heat one tank or cool the other.
(With a water to water heat pump, it is also
possible to pump heat from one tank to the
other for true “simultaneous” heating and
cooling, although such a system is more
complex to install.)
Advantages Drawbacks
No seasonal switchover is required. Heating and cooling distribution devices need to be separate
devices or flow directed with the addition of zone 3-way valves.
Works well for heating and cooling using 4-pipe air handlers
(and in-floor heating). Requires more mechanical room space.
Higher equipment cost than a 1-tank system.
For space heating/cooling heat pumps, year-round dedicated
domestic hot water preheating is possible.
Plumbing and control may get complicated if using a standalone
heating device (like a boiler) for auxiliary heat.
Simultaneous heating and cooling is possible; heating and cool-
ing in close proximity is practical
Plumbing and control may get complicated for multiple heat
pumps connected to same buffer tanks.
This is an important design choice that needs to be made when planning an installation. These systems are described more
fully in the following chapters.

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ATWC Sizing
Even in northern heating dominant climates, it should
be ensured that 100% of the cooling load will be covered
when sizing the heat pump. (Note that ATWC models with
the double wall condenser option, used for dedicated DHW
heating, should not be used for space cooling since the double
wall heat exchanger is not optimized for extended periods of
cooling operation.)
Auxiliary Heat Sizing
The easiest way to provide backup heat for new installa-
tions is by installing a buffer tank that has electric elements.
Buffer tanks with elements that are certified for space heating
use are available as accessories from Maritime Geothermal
Ltd., or others may be used.
An element size should be chosen that covers 100% of the
coldest day heat load, according to the heat loss analysis men-
tioned in the last section. This is because the elements will take
over heating duty if the outdoor temperature falls below the mini-
mum for heat pump operation (-7°F/-22°C), or if the heat pump
experiences a problem. If a heat loss analysis is not available,
the following table may be used as a guide.
This is an estimate of which unit size is required for a typi-
cal two-level home (main level and below grade basement) with
R-20 walls, R-40 ceiling and average size and number of win-
dows. The Heated Area is the area of the main level. The table
accounts for a basement the same size as the heated area.
It is highly recommended that a heat loss/gain analy-
sis be performed by a qualified person with software using
the CSA F-280 or Manual J methods before selecting a heat
pump size. The analysis will result in a heat load for the cold-
est day, which is influenced by, for example, the number of lev-
els, the size of the windows, the orientation of the home, at-
tached garage, bonus rooms, walk-out basement, and coldest
outdoor temperature for the region.
In northern climates, a heat pump model size can be se-
lected by matching the calculated heat load to the heat pump’s
heating capacity at an outdoor temperature of 35°F (1.7°C) and
the expected indoor water temperature of 140°F (60°C) to 160°F
(71°C). These numbers can be found in the detailed perfor-
mance tables in the Model Specific Information section later in
this manual. This sizing will result in a good compromise be-
tween covering as much of the cold weather heat load as possi-
ble without utilizing backup heat, while minimizing excessive
cycling (turning on and off frequently) during moderate outdoor
temperatures.
It should be noted that sizing an air source heat pump is
always a compromise between covering coldest-day heat load
and minimizing cycling due to over-capacity in warm weather.
In cooling dominant climates, the heat pump should be
similarly sized, by matching the calculated cooling load to the
standard capacity rating at an outdoor temperature that matches
the local maximum outdoor temperature. The difference here is
that it is necessary to cover all of the cooling load, since there is
no backup cooling.
Air Source Heat Pumps
Since it is harder to extract heat from colder outdoor air,
any air source heat pump will have its lowest heating capacity
on cold days when building heat load is the highest. It is not
generally possible to oversize an air source heat pump to cover
100% of the coldest day heat load, since this would mean ex-
cessive compressor short-cycling during moderate outdoor
weather when heat pump capacity is much higher and heat load
is much lower.
For these reasons, it should be expected that any air
source heat pump will need auxiliary heat on the coldest
days.
Heat Pump Sizing for
Space Heating/Cooling
The table shows the size of home each air source heat
pump model size is generally suitable for, in northern climates.
TABLE 1 - Heat Pump Size vs. Heated Area
Model sq.ft. m2
45 1,400 130
65 2,600 240
75 3,100 290
100 (3 phase only) 4,200 390
55 2,000 185
80 3,500 325
TABLE 2 - Auxiliary Heat Sizing
Model
Tank Element Size
Recommended AltSource Tank Available
45 10 kW 12 kW (50 gal)
65 15 kW 15 kW (70 gal)
75 20 kW 20 kW (70 gal)
100 (3ph only) 28 kW -
55 12 kW 15 kW (70 gal)
80 20 kW 20 kW (70 gal)
For retrofits, the existing heating device (e.g. an electric or
gas boiler) may be used for auxiliary heat. It should be set up to
be activated as heating stage 2 by the heat pump as described
in the Wiring section, and piped in a parallel arrangement as per
the diagram in the Piping section.

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Installation Basics
Sample Bill of Materials -
ATWC Series
FROM MARITIME GEOTHERMAL
• ATWC SERIES HEAT PUMP W/ACEC OUTDOOR UNIT
• SHIELDED DOUBLE TWISTED PAIR WIRE
• BUFFER TANK W/ELEMENTS 12/15/20 kW
OPTIONAL FROM MARITIME GEOTHERMAL
• ANTI-VIBRATION PAD
• COMPRESSOR SOUND JACKETS (2)
• COMPRESSOR SECURE STARTS (2)
• AHW-65 AIR HANDLER(S)
ELECTRICAL
• HEAT PUMP SERVICE WIRE: 3-3, 4-3, 6-3, OR 8-3
• BUFFER TANK ELEMENT SERVICE WIRE
• 14-2 OUTDOOR RATED WIRE W/ DISCONNECT
SWITCH FOR OUTDOOR UNIT
• HEAT PUMP BREAKER: 40 TO 100A
• BUFFER TANK ELEMENT BREAKER
• ELEMENT CONTACTOR & ELEC. BOX
(IF NOT USING TANK W/ DRY CONTACTS)
• THERMOSTAT WIRE 18-4
• THERMOSTAT WIRE 18-2
• FORK TERMINALS FOR TSTAT WIRE (6)
REFRIGERATION
• 1/2” & 7/8” (OR 3/8” & 3/4”) ACR TUBING
• PIPE INSULATION
• EXTRA R410A & R134a REFR. FOR LINESETS >20 FT
HYDRONICS
• CIRCULATOR: HEAT PUMP TO TANK
• PIPE & FITTINGS: HEAT PUMP TO TANK
• ZONES CIRCULATOR(S)
• ZONE TRANSFORMER & CIRC CONTACTOR
• ZONE VALVES (IF NOT INDIVIDUAL PUMPS)
• ZONE PIPING
• OTHER AIR HANDLERS, DUCTING
• ZONE THERMOSTATS
• RELAYS OR ZONE CONTROLLER
• ZONE SUPPLY & RETURN HEADERS:
1” COPPER PIPE & FITTINGS
• PIPE & FITTINGS TO ZONES
• EXPANSION TANK
• 2” STYROFOAM INSUL. (IF PAD NOT PURCHASED)
Unpacking the Unit
When the 2-piece heat pump reaches its destination it
should be unpacked to determine if any damage has occurred
during shipment. Any visible damage should be noted on the
carrier's freight bill and a suitable claim filed at once.
Indoor Unit Placement
The the indoor unit should be placed near the outdoor unit
to keep the two refrigerant line sets as short as possible. The
line sets have a maximum length of 70 ft (21 m) but should be
as short as possible for maximum efficiency.
The front and two side access panels should remain clear
of obstruction for a distance of two feet to facilitate servicing
and general maintenance. No access is required on the back
side.
An anti-vibration pad, available as an accessory, or a
piece of 2” styrofoam should be placed under the unit. This will
deaden vibrations and protect the cabinet from rusting.
* See Piping chapter for an annotated copy of this diagram

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Outdoor Unit Placement
The ACEC unit must be placed outdoors, with the fans
pointing away from the building. There is a detachable cover for
the piping and wiring which automatically places the unit 12
inches (30 cm) away from the building, which is the recom-
mended spacing. If necessary, the unit can be placed 8 inches
(20 cm) from the building: the cover can be shortened by
cutting the tabs and removing one section. Be aware that if
mounted at less than 12 inches from building, there is a risk of
frost forming on the wall during defrost under certain conditions.
Be sure there are no obstructions around the perimeter of the
back, so that return airflow is unimpeded.
There should be little or no obstruction in the fan (front)
direction for at least 10 ft (3 m), and preferably 16 ft (5 m), other-
wise airflow and therefore overall performance will be reduced.
In addition, there should be at least two feet (0.6 m) of
clearance on the electrical box and refrigeration piping side of
the unit to facilitate servicing and general maintenance.
The outdoor unit must be bolted down to prevent a tipping
hazard. See next section.
Note that no field installed filter-dryer is required.
Leg Kit Installation
Outdoor Unit Mounting Height
The outdoor unit must remain clear of snow and ice at all
times. Good performance depends on good airflow, which of
course cannot be achieved if the unit is buried in snow and re-
frozen defrost condensate.
1. If there is less than ~4” (10 cm) of snow accumulation
expected, the unit could be mounted directly on a con-
crete pad. This is not recommended in cold climates,
since ongoing care would be required to ensure re-
frozen condensate does not build up under unit.
2. The unit can be mounted on angle brackets attached
to the side of a building. Be sure to adhere to the
minimum clearance requirement of 8-12” (20-30 cm),
and use brackets designed for twice the unit weight.
3. Two leg kits which add either 15” (38 cm) or 30” (76
cm) of additional height are available as an acces-
sory. For ATWC-65 and larger which use a larger
outdoor unit, only the shorter leg kit is available.
To attach the legs, slide the leg over the outside of the two
existing cabinet legs and affix with the kit’s three SS bolts and
flat washers.
Whether or not a foot kit is used, be sure to mount the unit
using the 4 rubber grommets included with the unit, to dampen
any vibration. The unit must be fastened to its mounting surface
with four bolts through these grommets to prevent a tipping
hazard due to impact or high wind.
IMPORTANT
NOTE:
The line set
between the
indoor and
outdoor units
must not be
longer than
70 ft (21 m).
Outdoor Unit
Fan Orientation
Outdoor Fan Speed Reduction
Should fan noise be a concern, for example if the outdoor
unit is mounted near a frequently open window, the outdoor fan
speed can be reduced (up to a maximum of 25%). This should
only be done if necessary, since a small loss in efficiency will
result.
The fan speed can be reduced via the LCD (see LCD In-
terface & Menus section) or PC App (see PC Application
section).
Line Sets
The ATWC-series is different than most split air source
heat pumps in that 2 field installed line sets (4 refrigerant pipes
total) are required to transport the 2 different refrigerants used in
the cascade refrigeration system. See Outdoor Unit Line Sets
chapter.
connections
inside unit

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Average Maximum Snow Depth - Canada (1979-1997)
Source: Natural Resources Canada

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Wiring
IMPORTANT NOTE: A properly qualified
electrician should be retained for all
connections to the heat pump and associat-
ed controls. The connections to the unit
MUST CONFORM TO LOCAL CODES.
TABLE 3 - Power Supply Connections
Line Description Voltages
L1 Line 1 All
L2 Line 2 All
L3 Line 3 3-phase only
N Neutral
For 208/230-1-60, 208-3-60:
only required if connecting 115v
circulators.
Required for 460-3-60, 380-3-50.
GND Ground All (connect to ground lug)
Indoor Unit Power Supply Connections
Power supply for the heat pump from the breaker panel is
supplied to the indoor unit. The unit has a concentric power
supply knockouts, as well as knockouts and holes for connec-
tions to circulation pumps, controls, optional aquastat, and pow-
er and signal connections to the outdoor unit. All wiring is con-
nected to the indoor unit at the top rear, and fed to the front
electrical box through a wire channel under the top.
A schematic diagram (SCH) and electrical box layout
diagram (ELB) can be found on the electrical box cover of the
unit as well as in the Model Specific Information section of this
manual.
The Electrical Tables in the Model Specific Information
section contain information about the wire and breaker size.
Indoor Loop Circulator Pump Wiring
The indoor unit has provisions for connecting the indoor
circulator pump (between the heat pump and buffer/DHW tank)
so that it will be turned on whenever the compressor(s) operate.
Connect the circulator pump module to the appropriate terminals
(115V or 230V) on the terminal strip marked Indoor Circulator
Pumps, as per the voltage of the circulator pump. Ground
wires should be connected to the ground lug in the electrical
box. Ensure that the total current draw does not exceed the
value indicated on the label in the heat pump electrical box.
For 460VAC models, only 277VAC circulators may be
powered directly from the heat pump. If other voltage circulators
are used, they must be powered using an external contactor
actuated by the ICR terminal on the left side of the control board
and the C (24V ground) terminal.
TABLE 4 - Outdoor Unit Power Supply Connections
Line Description
L1 Supply line
L2 Supply line
GND Ground
Use a 2-conductor outdoor rated 14ga cable.
IMPORTANT NOTE: Most codes require a
disconnect switch visible and/or reachable
from the outdoor unit to be installed in the
power supply cable. If the switch has fuses
or breakers they must be no more than 10A.
Outdoor Unit: Power Connections
The ACEC outdoor unit must be powered from the indoor
unit. The power supply for the ACEC-45/55 unit is 208-277VAC,
50/60Hz, and for ACEC-65 to100 is 208/230-1-60. The ATWC
and ACEC units have matching terminal strips for these connec-
tions. Use a two conductor, minimum 14ga outdoor rated cable
for this connection. Refer to diagram.
Control Transformer
The low voltage controls, including the control board, are
powered by a 100VA class II transformer. 208/230-1-60 and
208-3-60 models have a resettable breaker on the secondary
side for circuit protection. Should the breaker trip, locate and
correct the problem and then reset the breaker by pressing it.
All other voltage models have primary and secondary fus-
es for circuit protection.
IMPORTANT NOTE: For 208/230VAC-1-60
units, if connecting to 208VAC power supply
move the red wire connected to the 240 ter-
minal of the transformer to the 208 terminal.
TABLE 6 - Control Transformer
Voltage Low Voltage Circuit Protection
(1) 208/230-1-60 Resettable breaker on transformer
(2) 208-3-60 Resettable breaker on transformer
(4) 460-3-60 Primary / Secondary fuses
(6) 220-1-50 Primary / Secondary fuses
(7) 380-3-50 Primary / Secondary fuses
OUTDOOR DISCONNECT SWITCH IS A
SAFETY DEVICE ONLY. Turn off breaker to
indoor unit before servicing to avoid costly
damage to electronic control board.
IMPORTANT NOTE FOR 3-PHASE UNITS: If
on startup compressor is noisy and not
pumping, reverse L1 and L2 supply wires.
TABLE 5 - Indoor Loop Circulator Connections
Signal Description
115V
230V
Use a 2-conductor 14ga cable.
Connection for 115V circulator
Connection for 230V circulator
115/230 Connection for 115V or 230V circulator

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Setpoint Control Connections
If using the on-board Setpoint Control routine with sam-
pling to control buffer tank temperature, no external temperature
probe or aquastat is required. In this case, only one control
connection is required, a dry contact from R to O on terminal
strip to switch the heat pump into cooling mode. C may be used
in powering relays as shown in diagrams on following pages.
Note that in a one tank heating/cooling system, the O
signal must be continuously provided during cooling sea-
son. If it toggles with demand, the tank will be repeatedly
heated and cooled, resulting in high power usage.
TABLE 9 - Setpoint Control: Aux. Connections
Signal Description
R
D1
D2 Hydronic Auxiliary Contactor
D1 Hydronic Auxiliary dry contacts
D2
H1 Hydronic Auxiliary ONLY dry contacts
(for high temperature auxiliary heat)
H2
Use a 2-conductor 18ga cable.
Connect with wire jumper and also connect to
Hydronic Auxiliary Contactor
TABLE 8 - Setpoint Control Connections
Signal Description
C 24VAC common (ground)
R 24VAC hot
O Cooling Mode (Reversing Valve)
Use a 3-conductor 18ga cable.
An external temperature probe may be used with the on-
board Setpoint Control routine; this is the required method if
using an ultra-high temperature boiler in parallel with heat
pump on terminals H1-H2. Or two probes (one for hot tank
and one for cold tank) may be used. This is HTS/CTS Setpoint
Control; see Piping and Operation sections for details.
Setpoint Control: Aux. Connections
When using Setpoint Control, there are 3 methods for acti-
vating hydronic auxiliary heat. See diagram on a following
page.
First, if using a heating device that doesn’t have its own
electronic controller or control transformer, e.g. a bare heating
element in the buffer tank: connect coil of an external contactor
to R and D2 on terminal strip, and jumper R to D1 as shown.
This contactor can then be used by the heat pump to toggle high
voltage power to the heating device when auxiliary heat is re-
quired. Default will be OFF when heat pump is powered off.
Second, a dry contact on terminals D1 and D2 is available,
to actuate a heating device that has its own controller and trans-
former. In general, these types of devices will have their own
electronic temperature controller. Connection will be made to
that device’s E-E terminals or similar. D1-D2 defaults to ON
when heat pump is powered off. Therefore, it is necessary to
set the temperature control on the external heating device to a
limiting value, e.g. 125°F, and adjust its settings so it is only
activated by the heat pump’s controller. This method should be
used for the Thermo2000 AltSource tank that is available
from Maritime Geothermal as an accessory; see the setup
instruction sheet that comes with tank and on following page.
Third, a dry contact is available on terminals H1 and H2. It
operates similarly to D1-D2 above, but is only activated when
auxiliary heat is requested AND the compressor is off (i.e. when
the outdoor temperature has dropped below the selectable mini-
mum operating temperature). This should be used to actuate
very high temperature heating devices that would interfere with
heat pump operation if run simultaneously. HTS/CTS control
with tank sensor should be used. Like D1-D2, H1-H2 defaults
to ON.
D1-D2 and H1-H2 default to ON and so must be
used with an auxiliary heating device that has a
HIGH TEMPERATURE LIMITER to avoid a seri-
ous safety hazard.
If it is not desired to have D1-D2 default to ON when heat
pump is powered off, make the following wiring changes in the
heat pump’s electrical box, while referring to the Wiring/
Schematic diagram in the Model Specific Information chap-
ter.
 Find the light brown wire connected between terminal strip
terminal D1 and the Elec. Aux. Relay. Move it from pin 5 to
pin 2 of the relay.
 Find the purple wire connected between the left side of the
control board and the Elec. Aux. Relay. Move if from termi-
nal L4 (NOT_HYD_AUX) to DO_2 (HYD_AUX) on the con-
trol board.
Now D1-D2 will work as before, but will default to OFF when
heat pump is off.
BACnet Connections
If using BACnet for external control of heating/cooling de-
mand and/or monitoring of status, use a shielded twisted pair to
the connector at the bottom left of control board. There is an
optional termination jumper located above the connector.
See the BACnet Interface section for details.
TABLE 7 - BACnet Connections
Line Description
A Communication +
B Communication -
GND Ground
Use a shielded twisted pair cable.

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Aquastat Connections (Optional)
Most installations will use the internal Setpoint Control
routine to control buffer tank temperature, in which case no aq-
uastat is required. However, an aquastat or aquastats can be
used if required, for example if heating two loops with different
setpoint temperatures. This is Signals or Hardwired Control.
C, R, and O connections are located on the main ter-
minal strip. Y1A is located at right side towards the top of the
control board. This is shown on the wiring (SCH) diagram in the
Model Specific Information section. The external device
needs to send the 24VAC signal from R back to Y1A to call for
the single capacity stage of hydronic heating, and R back to O
to activate cooling mode. C is the common or ground terminal
for use in powering the external device.
TABLE 11 - Aquastat (Signals Control) Connections
Signal Description
O Cooling Mode (Reversing Valve)
C 24VAC common (ground)
R 24VAC hot
Y1A Compressor ON (Part Load)
Use an 18ga cable.
Disable Switch (field installed)
A switch to disable demand from the control system may
be installed. On control board, jumper COM_IN to GND, and
toggle 12VDC to IN_SPARE to disable. See the main wiring
diagram in the Model Specific Information section.
Outdoor Unit: Signal Connections
The speed of the fans and the two heating mode expan-
sion valves (EEVs) in the outdoor unit must be controlled by the
control board in the indoor unit, and a temperature sensor must
be read. For ATWC/ATW2 series, this is done by MODBUS
communications between the main control board in the indoor
unit and a small daughter board in the outdoor unit. So the
number of required signal wires is reduced.
Connect the supplied double twisted pair shielded outdoor
rated cable between the terminal strips in the indoor and
outdoor units. The shield itself is connected only to the indoor
unit; do not connect the shield ground to the outdoor unit
(there is no terminal for it). Cut the shield short at the cable
sheath in the outdoor unit.
TABLE 10 - Outdoor Unit Signal Connections
Signal Description
A MODBUS Communications
(use 1 twisted pair)
B
12VDC
GND
Shield
Cable shield: connect only to the indoor
unit. In the outdoor unit, cut the shield
short at the cable sheath.
Use provided double twisted pair shielded outdoor
rated cable.
Power to MODBUS board in outdoor unit
AVOID INSULATION NICKS ON INDIVIDUAL
OUTDOOR UNIT SIGNAL WIRES
SLICE A LINE ALONG WIRE SHEATHING TO-
WARDS THE END, THEN PULL IT AWAY FROM
THE WIRES BEFORE CUTTING OFF.
DO NOT CUT A CIRCLE WITH UTILITY KNIFE
BEFORE SEPARATING SHEATHING FROM BUN-
DLED SIGNAL WIRES.
Defrost Indicator (field installed)
A 24VAC signal is available for an externally installed
indicator, which is active when the heat pump is in defrost
mode. This may be useful for the building operator or home-
owner, to know when buffer tank is being cooled instead of heat-
ed.
The indicator may be installed between terminals SH
and C(SH) at the lower left side of control board.

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Piping
Indoor Loop Water Lines
The connections for the Indoor Loop circuit are 1” or
1-1/4” brass FNPT. They are labelled as INDOOR IN and
INDOOR OUT. The ports are located on the left side of the
unit near the back.
Recommended buffer tank piping is shown in diagrams on
following pages. They show all of the recommended compo-
nents as well as where they should be placed. If other types of
components are used or connected differently, this is done at
user’s discretion with the caution that heat pump may or may
not work properly.
Note there is a separate set of piping diagrams for
DHW heating heat pumps with the double wall condenser
option.
NOTE: It is recommended that the water lines between the
heat pump and the buffer tank be copper or other high tempera-
ture piping.
NOTE: Care should be taken when routing the water lines to
ensure that adequate access to the heat pump is maintained so
as to not compromise ease of serviceability.
The minimum buffer tank size should follow the rule of 8
US gallons per ton of heat pump capacity. The following table
shows the minimum buffer tank size for each heat pump along
with the recommended size. The recommended size will mini-
mize the number of starts per hour and provide longer runtimes
for improved efficiency.
TABLE 12 - Buffer Tank Size
Heat Pump Size Minimum Size
gal (L)
Recommended Size
gal (L)
45 24 (90) 50 (190)
55 32 (120) 70 (265)
75 48 (180) 70 (265)
100 70 (265) 100 (380)
If a tank size is not available, use the next size larger tank.
65 40 (150) 70 (265)
80 52 (200) 70 (265)
Number of Tanks
All dedicated DHW heat pumps (with the double wall con-
denser option) require one DHW holding tank, equivalent in
function to the single buffer tank systems discussed below.
All space heating/cooling heat pumps with single wall con-
denser require at least one buffer tank. If there is one buffer
tank, it will contain the heated or chilled water. The water in the
tank will be chilled when the “O” signal is activated. This buffer
tank may have electric elements for auxiliary heat, or an existing
boiler may be used. See piping diagrams on following pages.
If there is need for heating and cooling simultaneously or
in close proximity, or if need for a seasonal switchover is to be
avoided, two buffer tanks maybe installed. One will be always
be heated, and one will be always be chilled, controlled using
the on-board Setpoint Control routine. This routine has two op-
tions: the “O” signal from an external controller may be used to
tell the heat pump to switch to cooling mode and cool the cold
tank, or the “Auto Maintain” function may be used to automati-
cally maintain both the hot and cold tanks without external input.
See Operation section, and piping diagrams on following pages.
See the chapter One or Two Buffer Tanks? near the begin-
ning of this manual for a discussion of this topic.

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