Nordic ATW Series Manual

ISSUE 02: 7-Dec-2021 Page 1 001970MAN-04
Maritime Geothermal Ltd.
P.O. Box 2555, 170 Plantation Road
Petitcodiac, NB E4Z 6H4
[phone]
ATW-Series
Reversing Central Air to Water Heat Pump
Two-Stage R410a
Model Sizes 25-75
[email protected]
www.nordicghp.com
001970MAN-04
ISSUE 02: 7-Dec-2021
Installation and Service Manual

ISSUE 02: 7-Dec-2021 Page 2 001970MAN-04
Series:
ATW = Air To Water heat pump
Nominal Size:
25 = 020 compressor
45 = 030 compressor
55 = 040 compressor
65 = 051 compressor
75 = 060 compressor
Functions:
H = Heating
AC = Active Cooling
W = Domestic Hot Water
Refrigerant:
P = R410a
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:
C = Copper
Y = CuNi coil & piping
Z = CuNi coil only
Revision:
01, 02 etc.
ATW—75—HACW—P—1T—C—xx
Compressor:
S = 1 Stage Scroll
T = 2 Stage 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
ACE—75—P—1/6—KDE—xx
Series:
ACE = All weather Condenser / Evaporator
(air source outdoor unit)
Nominal Size:
25 = for AT_-25
45 = for AT_-45
55 = for AT_-55
65 = for AT_-65
75 = for AT_-75
Voltage Code:
1/6 = 220~277-1-50/60
Air Coil:
S = Standard
K = Coated
Fan Type:
D = Direct Drive
Fan Motor:
E = ECM (Variable Speed)
Revision:
01, 02 etc.
Refrigerant:
P = R410a

ISSUE 02: 7-Dec-2021 Page 3 001970MAN-04
APPLICATION TABLE - INDOOR UNIT
SIZE FUNCTION REFRIGERANT VOLTAGE COMPRESSOR INDOOR
COIL
REVISIONS
ATW-25 H A C W P
1
2
4
6
7
T
C
Y
Z
03 04
ATW-45 H A C W P
1
2
4
6
7
T
C
Y
Z
03 04
ATW-55 H A C W P
1
2
4
6
7
T
C
Y
Z
03 04
ATW-65 H A C W P
1
2
4
6
7
T
C
Y
Z
03 04
ATW-75 H A C W P
1
2
4
7
C
Y
Z
03 04
6 S
This manual applies only to the models and revisions listed in this table.
T
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 V3.60+ MGT GEN2 PC APP V2.00+
APPLICATION TABLE - OUTDOOR UNIT
MODEL REFRIGERANT VOLTAGE AIR COIL BLOWER TYPE BLOWER MOTOR REVISIONS
ACE-45 P 1/6 S
K D E 03 04
ACE-55 P 1/6 S
K D E 03 04
ACE-65 P 1/6 S
K D E 08
ACE-75 P 1/6 S
K D E 08
This manual applies only to the models and revisions listed in this table.

ISSUE 02: 7-Dec-2021 Page 4 001970MAN-04
Table of Contents
Tables & Documents ........................................................ 5
ATW 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
ATW Sizing .......................................................................... 8
Air Source Heat Pumps .......................................................... 8
Heat Pump Sizing ................................................................... 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
Outdoor Fan Speed Reduction ............................................. 10
Outdoor Unit Mounting Height .............................................. 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
002019CDG - Typ. ATW 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
002069CDG - Typ. Heating Only Zone Wiring (Signals) ........ 19
002070CDG - Typ. Htg/Cooling Zone Wiring (Signals) .......... 20
Piping ................................................................................. 21
Number of Tanks .................................................................. 21
Indoor Loop Water Lines ........................................................ 21
Domestic Hot Water (Desuperheater) Connections .............. 21
002239PDG - Typical Piping Connections - ATW Series ....... 22
002366PDG - Recommended Buffer Tank Piping ................. 23
002528PDG - Buffer Tank Piping - Multiple Units .................. 24
002252PDG - 2 Tank Piping with a Reversing Heat Pump .... 25
002527PDG - 2 Tank Piping w/Multiple Rev. Heat Pumps .... 26
002367PDG - Auxiliary Boiler Piping ..................................... 27
000530PDG - Typical Zone Types ......................................... 28
001055PDG - Connection to On-Demand DHW Tank ........... 29
000970PDG - Desup. Conn. to DHW Pre-Heat Tank ............ 30
002384PDG - DHW Pre-Heat Tank - Multiple Units .............. 31
Outdoor Unit Line Set ..................................................... 32
Line Set Interconnect Tubing ................................................ 32
Indoor/Outdoor Unit Connections .......................................... 32
Oil Traps ............................................................................... 32
Filter-Dryer ............................................................................ 32
Pipe Insulation ...................................................................... 33
Silver Soldering Line Sets ..................................................... 33
Pressure Testing ................................................................... 33
Vacuuming the System .......................................................... 33
Charging the System ............................................................. 33
001983CDG - Typical ATW Line Set Connections ................ 34
Operation ........................................................................... 35
1. BACnet Control ................................................................. 35
2. Signals / Hardwired Control .............................................. 35
3. Setpoint Control ................................................................ 35
Setpoint Control Method 1 - Indoor Loop (ICR), One Tank .... 35
Typical Temperature Setpoints ........................................... 36
Top Up S1 Function ........................................................... 36
Summer Setback ................................................................ 36
Hydronic Auxiliary in Defrost .............................................. 36
Outdoor Reset .................................................................... 37
Setpoint Control Method 2 - Indoor Loop (ICR), 2 Tanks ....... 37
Setpoint Control Method 3 - External HTS/CTS, One Tank .. 38
Setpoint Control Method 4 - External HTS/CTS, 2 Tanks ..... 39
PC Application (PC App) ............................................... 40
LCD Interface & Menus .................................................. 52
BACnet Interface .............................................................. 54
Startup Procedure ........................................................... 58
Pre-start Inspection ............................................................... 58
Unit Startup ........................................................................... 59
Startup Record ...................................................................... 60
Routine Maintenance ...................................................... 61
Troubleshooting Guide .................................................. 62
Repair Procedures .......................................................... 72
Pumpdown Procedure .......................................................... 72
General Repair Procedure .................................................... 72
Vacuuming & Charging Procedure ....................................... 72
Compressor Replacement Procedure ................................... 73
Outdoor Fan Replacement Procedure .................................. 73
Control Board Replacement Procedure ................................ 74
LCD Interface (Display) Board Replacement Procedure ....... 75
Model Specific Information ........................................... 76
Shipping Information ............................................................. 76
Refrigerant Charge ............................................................... 76
Indoor Loop Flow Rates ........................................................ 76
Operating Temperature Limits .............................................. 76
Sound Levels (dBA) .............................................................. 76
Pressure Drop Data ............................................................... 77
Standard Capacity Ratings ................................................... 79
Performance Tables .............................................................. 80
Electrical Specifications ........................................................ 85
Wiring Diagram (208/230-1-60) ............................................ 86
Electrical Box Layout (208/230-1-60) .................................... 87
Wiring Diagram (208-3-60) ................................................... 88
Electrical Box Layout (208-3-60) ........................................... 89
Wiring Diagram (460-3-60) .................................................... 90
Electrical Box Layout (460-3-60) ........................................... 91
ACE-45/55 Wiring Diagram .................................................... 92
ACE-65/75 Wiring Diagram .................................................... 92
ATW-Series Refrigeration Circuit - Heating Mode ................. 93
ATW-Series Refrigeration Circuit - Cooling/Defrost Mode ..... 94
Dimensions: ATW-25/45 ........................................................ 95
Dimensions: ATW-55 ............................................................. 97
Dimensions: ATW-65/75 ........................................................ 99
Appendix A: Control Board Description ................... 101
Appendix B: USB Driver Installation ......................... 105
Appendix C: PC App Installation ............................... 106
Appendix D: Updating Firmware ................................ 107
Warranty .......................................................................... 110

ISSUE 02: 7-Dec-2021 Page 5 001970MAN-04
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 ................................................................................................................... 21
Table 13 - Line Set Sizing ..................................................................................................................... 32
Table 14a - 3-way Service Valve Tooling .............................................................................................. 32
Table 14b - 3-way Service Valve Torques ............................................................................................. 32
Table 15 - Extra Charge for Model Sizes 25-45 .................................................................................... 33
Table 16 - Extra Charge for Model Sizes 55-75 .................................................................................... 33
Table 17 - Typical Temperature Setpoints ............................................................................................. 36
Table 18 - Maximum Output Temperature ............................................................................................. 36
Table 19 - BACnet Objects - Control Signals (Read/Write) .................................................................... 54
Table 20 - BACnet Objects - Operation Mode Description (Read Only) ................................................. 54
Table 21 - BACnet Objects - Limits Description (Read Only) ................................................................. 54
Table 22 - BACnet Objects - Data (Read Only) ...................................................................................... 55
Table 23 - BACnet Objects - Defrost Mode Description (Read Only) ..................................................... 56
Table 24 - BACnet Objects - Alarm Descriptions (Read Only) ............................................................... 56
Table 25 - BACnet Objects - Fault Descriptions (Read Only) ................................................................. 57
Table 26 - Shipping Information (Indoor Unit) ........................................................................................ 76
Table 27 - Shipping Information (Outdoor Unit) ..................................................................................... 76
Table 28 - Refrigerant Charge ............................................................................................................... 76
Table 29 - Indoor Loop Flow Rates ....................................................................................................... 76
Table 30 - Operating Temperature Limits .............................................................................................. 76
Table 31 - Outdoor Unit Sound Levels (dBA) ........................................................................................ 76
Table 32 - Indoor Unit Sound Levels (dBA) ........................................................................................... 76
Table 33 - Loop Pressure Drop Data ..................................................................................................... 77
Table 34 - Standard Capacity Ratings - Heating ................................................................................... 79
Table 35 - Standard Capacity Ratings - Cooling ................................................................................... 79
Table 36 - ATW-Series Electrical Data .................................................................................................. 85
Table A1 - Control Board Connector Descriptions (Top) ...................................................................... 102
Table A2 - Control Board Connector Descriptions (Left Side) ............................................................ 102
Table A3 - Control Board Connector Descriptions (Bottom) ................................................................ 103
Table A4 - Control Board Connector Descriptions (Right Side) ........................................................... 104
002019CDG - Typical ATW 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
002069CDG - Typical Zone and Auxiliary Wiring with GEN2 Hardwired Option (Heating Only) ........... 19
002070CDG - Typical Zone and Auxiliary Wiring with GEN2 Hardwired Option (Heating & Cooling) ... 20
002239PDG - Typical Piping Connections - ATW Series ...................................................................... 22
002366PDG - Recommended Hydronic Buffer Tank Piping .................................................................. 23
002528PDG - Buffer Tank Piping - Multiple Units .................................................................................. 24
002252PDG - Two Tank Piping with a Reversing Heat Pump ............................................................... 25
002527PDG - Two Tank Piping with Multiple Reversing Heat Pumps .................................................... 26
002367PDG - Auxiliary Boiler Piping ..................................................................................................... 27
000530PDG - Typical Zone Types for Hydronic Applications ................................................................. 28
001055PDG - Single Unit Connection to On-Demand Domestic Hot Water Pre-Heat Tank .................. 29
000970PDG - Desuperheater Connection to DHW Pre-Heat Tank ....................................................... 30
002384PDG - Desuperheater Connection to DHW Pre-Heat Tank - Multiple Units .............................. 31
001983CDG - Typical ATW to Outdoor Unit Line Set Connections ....................................................... 34
001799SCH-04 - ATW-**-HACW-P-1*-* Schematic Diagram ................................................................. 86
001800ELB-02 - ATW-**-HACW-P-1*-* Electrical Box Diagram ............................................................ 87
002190SCH-04 - ATW-**-HACW-P-2*-* Schematic Diagram ................................................................. 88
002189ELB-02 - ATW-**-HACW-P-2*-* Electrical Box Diagram ............................................................ 89
002192SCH-04 - ATW-**-HACW-P-4*-* Schematic Diagram ................................................................. 90
002191ELB-02 - ATW-**-HACW-P-4*-* Electrical Box Diagram ............................................................ 91
001951SCH-01 - ACE Outdoor Unit Schematic Diagram ...................................................................... 92
002014SCH-01 - ACE 4-Fan Outdoor Unit Schematic Diagram ........................................................... 92
001840RCD-03 - ATW-Series Refrigeration Circuit Diagram - Heating Mode ........................................ 93
001841RCD-03 - ATW-Series Refrigeration Circuit Diagram - Cooling / Defrost Mode ......................... 94

ISSUE 02: 7-Dec-2021 Page 6 001970MAN-04
General Overview
The ATW-Series heat pump is an air source heat pump
that can heat water for a hydronic heating system, or heat and
cool water for a hydronic heating/cooling system. Applications
include in-floor heating, heating through low-temperature radia-
tors, pre-heating domestic hot water through the use of an indi-
rect tank with hydronic coil, and heating and cooling through
hydronic air handlers.
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 fan, expansion valve (EEV), and outdoor temperature sen-
sor. The remaining components, including the compressor and
all electronics, are contained in the indoor unit. This has several
advantages: minimal installation and service work must be per-
formed outdoors, important components are in the conditioned
space for longevity, antifreeze is not required in the hydronic
loop, no electric compressor heater is required, and heating
domestic hot water is possible (through a desuperheater circuit)
since the fresh water lines are inside and will never freeze.
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.
In additional to the main hydronic water heating/cooling
functions, there is a double-wall desuperheater for pre-heating
domestic hot water with ~5% of the heat pump’s capacity. This
function is only active when the heat pump is running for space
heating or cooling purposes. An energy-efficient bronze head
ECM circ pump for the desuperheater circuit is built in, along
with a temperature control to turn the pump off when the DHW
temperature reaches 140°F/60°C.
Two-stage scroll compressors are standard. The outdoor
air coil is e-coated for corrosion protection, and the coaxial hy-
dronic heat exchanger is copper / steel with optional CuNi inner
tube available for applications where water quality may be an
issue. 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 connectiv-
ity via the free PC App software, data logging & graphing, and
real time readout from electronic temperature & pressure sen-
sors.
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;
refer to the Defrost Operation section below. Refrigerant flow is
controlled by the EEV located in the outdoor unit while the EEV
in the indoor unit is fully open.
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.
ATW System Description
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 3 temperature control (stages 1
& 2 being the two compressor stages). The heat pump will turn
off and only the auxiliary heating system will operate if the out-
door temperature 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. Refrigerant flow is controlled by the
EEV located in the indoor unit while the EEV in the outdoor unit
is fully open. 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 Piping chapter for
an annotated copy of
this diagram

ISSUE 02: 7-Dec-2021 Page 7 001970MAN-04
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 tank for zone use during heating season, 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 systems 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).
Dedicated domestic hot water preheating is not possible in sum-
mer due to no hot tank being available.
Is the go-to option for heating-only 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). Takes more mechanical room space.
Higher equipment cost than a 1-tank system.
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.

ISSUE 02: 7-Dec-2021 Page 8 001970MAN-04
ATW Sizing
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
an indoor water temperature of 105°F (40.5°C) for concrete in-
floor heating or 120°F (49°C) for other heating types. These
numbers can be found in the detailed performance tables in the
Model Specific Information section later in this manual.
This sizing will result in a good compromise between covering
as much of the cold weather heat load as possible without utiliz-
ing 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.
Even in northern heating dominant climates, it should
be ensured that 100% of the cooling load will be covered
when sizing the heat pump.
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
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
25 800 75
55 2,000 185
65 2,600 240
75 3,100 290
45 1,400 130
TABLE 2 - Auxiliary Heat Sizing
Model
Tank Element Size
Recommended AltSource Tank Available
25 7 kW 12 kW (50 gal)
55 12 kW 15 kW (70 gal)
65 15 kW 15 kW (70 gal)
75 20 kW 20 kW (70 gal)
45 10 kW 12 kW (50 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 3 by the heat pump as described
in the Wiring section, and piped in a parallel arrangement as per
the diagram in the Piping section.

ISSUE 02: 7-Dec-2021 Page 9 001970MAN-04
Installation Basics
Sample Bill of Materials -
ATW Series
FROM MARITIME GEOTHERMAL
• ATW SERIES HEAT PUMP W/ACE OUTDOOR UNIT
• SHIELDED 18-8 WIRE
• BUFFER TANK W/ELEMENTS 12/15/20 kW
OPTIONAL FROM MARITIME GEOTHERMAL
• ANTI-VIBRATION PAD
• SOUND JACKET
• SECURE START
• AHW-65 AIR HANDLER(S)
DHW:
• PREHEAT TANK, 40 OR 60 GAL
• ½” COPPER PIPE
• ½” FITTINGS, BALL VALVES, BOILER DRAINS, CV
ELECTRICAL
• HEAT PUMP SERVICE WIRE: 6-3, 8-3, OR 10-3
• BUFFER TANK ELEMENT SERVICE WIRE
• 14-2 OUTDOOR RATED WIRE W/ DISCONNECT
SWITCH FOR OUTDOOR UNIT
• HEAT PUMP BREAKER
• 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 REFRIGERANT FOR LINESETS >20 FT
ZONES
• CIRCULATOR: HEAT PUMP TO TANK
• 1” PIPE & FITTINGS: HEAT PUMP TO TANK
• ZONES CIRCULATOR(S)
• ZONE TRANSFORMER & CIRC CONTACTOR
• ZONE VALVES (IF NOT INDIVIDUAL PUMPS)
• IN-FLOOR 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
For air to water models, the placement of the unit has neg-
ligible effect on the operation and efficiency of the system. It is
recommended that the unit be placed near where the intercon-
nect piping to the outdoor unit will be to keep the piping distance
to a minimum. See the 3D diagram in the Piping section for a
detailed typical component layout.
The front and right side access panels should remain clear
of obstruction for a distance of two feet to facilitate servicing
and general maintenance. Left side access is optional (since
the compressor may be accessed by swinging out the front-side
electrical box), and 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

ISSUE 02: 7-Dec-2021 Page 10 001970MAN-04
Outdoor Unit Placement
The ACE unit must be placed outdoors, with the fan point-
ing away from the building. It should be mounted where mois-
ture or ice under the unit will not be considered to be unsightly,
as might be the case on a paved walkway to the front door for
example.
For ACE-65/75, 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 recommended 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.
There are several ways to accomplish this. First, look up
how much snowfall is expected in your area, either from local
knowledge or weather data. The snowfall map included on next
page can be used as a rough guide for Canada.
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:
ACE-25/45/55 - first remove the three bolts with flat washers
that hold each foot plate in place. Leaving the foot plate in place
on the inside of the cabinet panel, slide the leg over the outside
of the panel and re-install the three bolts and flat washers.
ACE-65/75 -slide the leg over the outside of the two existing
cabinet legs and affix with the kit’s three SS bolts and flat wash-
ers.
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 exceed 70
ft (21 m) in length.
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).
Outdoor Unit
Fan Orientation
piping &
wiring
connections
inside unit

ISSUE 02: 7-Dec-2021 Page 11 001970MAN-04
Average Maximum Snow Depth - Canada (1979-1997)
Source: Natural Resources Canada

ISSUE 02: 7-Dec-2021 Page 12 001970MAN-04
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
GND Ground All (connect to ground lug)
* Only required if connecting 115VAC circulators.
N Neutral 208/230-1-60*, 208-3-60*,
460-3-60, 380-3-50
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 1.093” /
0.875” knockout for main power supply connection to the electri-
cal box. There are also five 7/8” knockouts and a 1/2” opening
with plastic grommet (grommet hole is 3/8”) for connections to
circulation pumps, controls, optional aquastat, and power and
signal connections to the outdoor unit.
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 tank) so that
it will be turned on whenever the compressor operates. Con-
nect the circulator pump module to the appropriate terminal pair
(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 5 - Indoor Loop Circulator Connections
Signal Description
115V Connection for 115V circulator
(requires Nneutral connection to heat pump)
115V
230V
230V
Use a 2-conductor 14ga cable.
Connection for 230V circulator
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 ACE outdoor unit is powered from the indoor unit.
The power supply for the ACE unit is 208 to 277VAC, 50/60Hz.
The ATW and ACE units have matching terminal strips for these
connections. Use a two conductor, minimum 14ga outdoor rat-
ed 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 in on
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.

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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
CA 24VAC common (ground)
1A Hydronic Auxiliary (hot)
D1 Hydronic Auxiliary dry contacts
D2
H1 Hydronic Auxiliary ONLY dry contacts
(for high temperature auxiliary heat)
H2
Use a 2-conductor 18ga cable.
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 a 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 Con-
trol; 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, a 24VAC signal on terminal 1A (with CA as ground/
common) is available to power the coil of an external contactor
to operate hydronic auxiliary heat. Choose this method 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. This signal can provide a maximum of 500mA at 24VAC.
1A defaults to 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
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. [It will share DO_2 with a brown wire.]
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.
The CA, RA, Y1A, and Y2A connections are located on
the right side towards the top of the control board. The O termi-
nal is found on the terminal strip (along with an alternate R and
C connection). This is shown on the wiring (SCH) diagram
in the Model Specific Information section. The external device
needs to send the 24VAC signal from RA back to the Y1A and
Y2A terminals to call for the two stages of hydronic heating,
and RA 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)
CA 24VAC common (ground)
RA 24VAC hot
Y1A Compressor ON (Part Load)
Y2A Compressor bump up to Stage 2 (Full 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 fan and the heating mode expansion
valve (EEV) in the outdoor unit are controlled by the control
board in the ATW indoor unit, and a temperature sensor is read.
Therefore, communication wiring is required.
Connect the supplied 8 conductor shielded outdoor rated
cable between the terminal strips in the indoor and outdoor
units. The shield ground wire 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 ground wire
short at the cable sheath in the outdoor unit.
TABLE 10 - Outdoor Unit Signal Connections
Signal Description
EEVR Electronic Expansion Valve (Red)
EEVG Electronic Expansion Valve (Green)
EEVW Electronic Expansion Valve (White)
EEVB Electronic Expansion Valve (Black)
TR Outdoor Temperature Sensor (Power)
TG Outdoor Temperature Sensor (Signal)
TB Outdoor Temperature Sensor (Ground)
PWM+ Outdoor Fan Control
Shield GND* Cable shield: see note
Use provided 8 conductor shielded outdoor rated cable.
* Connect only to the indoor unit. In the outdoor unit,
leave this wire unconnected and cut it short at the cable
sheath.
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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