Plan a practical path to lower-carbon domestic hot water with CO₂ heat-pump technology, Dalrada and ATI of New York.
Why start with hot water?
Showers, kitchens and other domestic uses create a daily heating requirement. The study starts with the volume, delivery temperature and timing of that demand, then includes storage and distribution losses. Domestic hot water (DHW) is a different service from space heating.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 5, 21
Local Law 97: building-level obligations
NYC Local Law 97 generally covers buildings exceeding 25,000 gross square feet, and certain groups of buildings exceeding 50,000 square feet. Emissions limits began in 2024 and become stricter in 2030. Coverage, exceptions and compliance pathways must be checked for the property.
NYC DOB — LL97 greenhouse gas emissions reductions
Evaluate the whole building
A heat pump changes the way heat is supplied. It does not, by itself, establish compliance or a savings result. Compare the proposed electricity use, retained fuel use and other building loads against the applicable emissions methodology.
NYC DOB — LL97 greenhouse gas emissions reductions · NYC DOB — LL97 building emissions limits
Start with the right records
Identify the property, floor area and use. For emissions reporting, NYC DOB now requires ESPM property types from 2026. Bring the existing LL97 assessment, if available, rather than assuming that a building name or size determines the complete pathway.
NYC DOB — LL97 building emissions limits
Local Law 97 is a New York City law. No automatic tax credit, refrigerant incentive, emissions reduction or compliance guarantee is offered here.
Information to prepare for your hot-water review: Property address; gross floor area; building use; BBL/BIN if known; current hot-water fuel; recent utility records; existing LL97 review.
Select an option below to explore the approach relevant to your project.
New construction: plan the hot-water plant
Coordinate demand, storage, distribution, electrical service and the equipment location while the building is still being designed. Space and access can be reserved before the layout becomes difficult to change.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 16-18, 21-25
Existing buildings: move DHW off the gas boiler
Focus the retrofit study on domestic hot water. A dedicated CO₂ heat-pump and storage arrangement can take over the DHW duty while the existing boiler continues to serve space heating. Backup and peak-demand responsibilities are defined in the project.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 5, 21
New construction: design low-temperature space heating
For a new building, evaluate radiant floors or low-temperature radiators with a deliberately cool return. This project targets a heat-pump inlet/return of 68–77°F (20–25°C) for the heating pathway; emitter ratings and the hydraulic arrangement must support that target.
Air-to-water CO₂ (R744) heating system — user’s manual — p. 22
One coordinated study
DHW serves taps and showers; space heating serves rooms. If both are requested, establish separate loads, operating temperatures and priorities. Any shared plant or simultaneous operation needs a specific hydraulic and control design.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 21-22
One 125-class R744 air-to-water platform. Each application has its own load, water temperatures and hydraulic design.
Information to prepare for your hot-water review: Choose new construction, existing building or space heating; identify whether DHW, space heating or both are required; give the project stage and target date.
Bring heat production, storage and daily demand together early, while the building design can still make room for them.
Begin with the load
Establish daily hot-water volume at a stated temperature, cold-water inlet temperature, peak draw periods and available recovery hours. A daily total alone cannot describe a morning peak.
Charge storage deliberately
The manual describes once-through gas coolers and stratified storage: cooler water enters the heat pump and heated water is stored for later use. Keeping the colder and hotter layers distinct helps preserve favorable inlet conditions.
Air-to-water CO₂ (R744) heating system — user’s manual — p. 5
Coordinate the building interfaces
Reserve a location with adequate airflow, service access, structural support and drainage. Plan insulated pipe routes, tank access, electrical capacity and a freeze-protection strategy with the design team.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 16-18, 23-28
Read the principle diagram
P03 shows a conceptual pressurized DHW arrangement derived from the manual’s tank examples. Coordinate the mixing assembly, recirculation strategy, potable-water interfaces and protective devices as part of the project design.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 4, 21, 24 · Dalrada DCE 125 brochure and performance curves — p. 1
The diagram is not a construction drawing. It does not establish tank capacity, equipment count, pipe size, structural loading or code acceptance.
Information to prepare for your hot-water review: DHW demand schedule; cold-water and delivery temperatures; roof and plant-room plans; structural constraints; electrical one-line; proposed pipe routes.
An air-to-water CO₂ heat pump for commercial hot-water production. Explore how it works, then evaluate the operating conditions relevant to your project.
Start cold. Store hot.
The transcritical CO₂ cycle is well suited to a large temperature rise through the gas cooler. A cold inlet and stratified hot-water storage are central to the system concept described in the manual.
Air-to-water CO₂ (R744) heating system — user’s manual — p. 5 · Dalrada DCE 125 brochure and performance curves — p. 1
A purpose-built thermal system
The compressor, air-side heat exchanger, gas cooler, expansion control, water pump and electronic controls work together to transfer heat from air into water. The integrated circulation pump regulates the water-side process.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 29, 32 · Dalrada DCE 125 brochure and performance curves — p. 1
Capacity is an operating-point value
“125” identifies the product class; it is not a promise of 125 kW in every condition. The supplied performance table changes capacity and COP with outdoor air, water inlet and water outlet temperatures. Use all three temperatures when comparing a project with the data.
AEHCO2/125 performance table
Location is part of the engineering
The unit needs unobstructed airflow, maintenance access, a suitable base and drainage. Rooftop placement is an option to study, not a requirement. A basement equipment room cannot be treated as an adequate air source without an engineered air path.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 7, 16-18, 27
Final equipment selection includes the project-specific electrical, hydraulic, structural and installation requirements.
Information to prepare for your hot-water review: Available location and access; electrical supply voltage/phase/frequency; structural information; equipment or quotation reference; photographs of the proposed site.
These details prepare a project conversation or study. Only the fields entered in an interactive tool are used in its calculation.
Outdoor air provides heat. Electricity drives the cycle. A heat exchanger transfers energy into the building’s water.
1. Absorb heat from air
The air-side heat exchanger acts as the evaporator. Refrigerant absorbs heat from the air before returning to the compressor. The fan and air path must remain unobstructed.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 8-9, 27, 29
2. Raise the refrigerant pressure
The compressor uses electricity to circulate and compress the CO₂. The manual describes a transcritical cycle. This is a sealed refrigerant circuit, not a water distribution pipe.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 5, 8, 32
3. Transfer heat into water
The gas cooler releases heat to the water stream. Water inlet temperature matters: colder inlet water supports better CO₂ cycle efficiency. Refrigerant and water remain in separate passages through the heat exchanger.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 5, 29 · Dalrada DCE 125 brochure and performance curves — p. 1
4. Expand and repeat
Expansion control reduces refrigerant pressure before the air-side heat exchanger. P05 is a functional cycle diagram: it does not reproduce every bypass, oil line, sensor or control sequence inside the unit.
Air-to-water CO₂ (R744) heating system — user’s manual — p. 32
What COP actually means
Heating COP is useful heat output divided by electrical input at the stated operating point. It is not an annual efficiency or a bill-saving percentage. Include external pumps and other auxiliaries consistently when estimating whole-system consumption.
Air-to-water CO₂ (R744) heating system — user’s manual — p. 9 · AEHCO2/125 performance table
The manual’s example COP of 6 is an explanatory energy balance, not a fixed rating for this model. Combined heating-and-cooling claims are outside this DHW-focused proposal.
Information to prepare for your hot-water review: Target water inlet/outlet temperatures; intended application; expected operating hours; auxiliary pump arrangement; required control interface.
Understand available output at your winter design condition, then coordinate recovery, storage and backup around the building’s needs.
Compare like with like
At a 50°F (10°C) water inlet and a 149°F (65°C) outlet, the supplied AEHCO2/125 table lists: 148.9 kW and COP 5.44 at 59°F (15°C) outdoor air; 86.3 kW and COP 2.79 at 19.4°F (-7°C); and 67.9 kW and COP 2.28 at 5°F (-15°C). These are table points, not seasonal averages.
AEHCO2/125 performance table — p. 1
Allow for defrost
The manual describes automatic defrost, approximately 2–15 minutes, with the fan stopped, and lists bypass defrost. It does not establish a guaranteed duration for each weather condition or whether the performance table includes defrost losses. Assess recovery and storage across these interruptions.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 10, 29
Protect the water side
Outdoor installation requires a shutdown and freeze-protection plan. The manual warns about draining water during prolonged shutdown below freezing. Any glycol or alternative protection arrangement needs manufacturer confirmation for the actual water circuit.
Air-to-water CO₂ (R744) heating system — user’s manual — p. 28
Respect the data boundary
The supplied table covers outdoor points from 5°F to 59°F (-15°C to 15°C), inlet points from 50°F to 122°F (10°C to 50°C), and outlet columns from 113°F to 185°F (45°C to 85°C), with invalid or missing cells. It is not a complete operating envelope.
AEHCO2/125 performance table — p. 1
Use the performance at the project’s actual air and water temperatures. Published maximum temperatures are not a promise of full rated capacity at every condition.
Information to prepare for your hot-water review: Location and outdoor design temperature with its source; winter cold-water temperature; production setpoint; recovery window; backup expectations; shutdown conditions.
Make heat when the system can produce it. Store energy for busy periods. Deliver hot water when the building needs it.
Production: set the charging conditions
Specify inlet and outlet water temperatures and how many hours are available to recover the required energy. Heating capacity is a rate; daily energy depends on the actual duty cycle and operating conditions.
AEHCO2/125 performance table
Storage: preserve useful layers
The manual emphasizes stratification for CO₂ water heating and shows both tank and pressure-tank arrangements. Storage should be evaluated against the time profile of demand, useful temperature range and recovery capacity—not a fixed number of gallons per heat pump.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 5, 21, 23
Distribution and recirculation
Insulated distribution carries water to fixtures. Recirculation returns water from the building to maintain service temperature, adding a thermal load even without fixture draw. Its return path must be designed without unnecessarily warming the heat pump inlet or destroying storage stratification.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 12, 18, 23
Control the available energy
Tank temperature sensing and the unit’s temperature/time controls govern charging in the manual. Setpoints, sensor positions and demand priorities must be coordinated. P07 leaves the recirculation connection and any return reheating as a project-specific design decision.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 10-13, 24, 26
Keep production volume separate from mixed delivery
A volume produced at the storage setpoint is not the same as the volume delivered after mixing with cold water. Demand data must identify its temperature basis before any tank or production calculation.
Air-to-water CO₂ (R744) heating system — user’s manual — p. 4
Production, storage and distribution must be sized together. Equipment flow is calculated at the stated water temperature rise; it is not the mixed flow available at fixtures.
Information to prepare for your hot-water review: Daily demand and its temperature basis; hourly or peak-period profile; storage setpoint; existing tank volumes; recirculation supply/return temperatures and operating hours.
A shower, a kitchen, a busy morning: the plant’s job is to support dependable hot water throughout the building.
Three temperatures, three purposes
Production temperature is the heat pump outlet. Storage temperature describes the tank condition. Delivery temperature is what the distribution and fixture controls provide. They should never be presented as interchangeable.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 4, 10-11, 21
Availability during the busy hour
Simultaneous showers or other demands draw on storage while the plant recovers. The design must also account for distribution losses and the building’s recirculation duty. An attractive production number alone does not establish the number of showers served.
Comfort also depends on the piping
Pipe length, insulation, balancing, recirculation operation and local mixing affect wait times and temperature stability. The building survey should record complaints and measurements at representative fixtures.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 12, 18, 23-24
High-temperature production is not shower temperature
The manual calls for hot/cold mixing and warns of scalding at high temperatures. Delivery protection and a water-management approach must be designed for the building. The heat pump’s maximum outlet rating is not a recommended fixture setpoint.
Air-to-water CO₂ (R744) heating system — user’s manual — p. 4
Review delivery temperature, availability and water management as building-system requirements, including the existing distribution network.
Information to prepare for your hot-water review: Fixture types and quantities; occupancy and simultaneous-use patterns; current wait times or complaints; delivery setpoints; available temperature measurements.
A new role for hot water in your existing building
Study a dedicated CO₂ heat-pump system for domestic hot water while assessing the existing space-heating system separately.
Separate the two duties
Identify how the gas boiler currently serves domestic hot water and space heating. The study separates the DHW production duty from the existing heating distribution, so each service has an explicit source and control strategy.
Build the DHW branch around cold inlet water
The CO₂ system heats cold water and charges stratified DHW storage. Distribution and recirculation are then coordinated with that storage. Existing tanks are reused only where ratings, condition and connections fit the design.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 5, 21, 23-25
Keep space heating on its existing branch
The existing radiator or steam heating distribution remains on its own boiler branch. The new CO₂ plant and storage serve DHW, with a separate source and control strategy for each service.
Plan the changeover
Define any retained DHW backup, peak support, outage sequence and controls before work starts. Check electrical capacity, airflow, structural support, drainage, access and available shutdown time. The drawing shows functional separation, not construction connections.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 16-18, 23-28
DHW load transfer does not imply that all gas use disappears. Space-heating fuel use and any retained DHW backup must remain in the building energy balance.
Information to prepare for your hot-water review: Existing schematic and nameplates; utility bills; tank and plant photographs; temperatures/pressures; electrical one-line; access survey; allowable shutdown window.
Consider low-temperature space heating as its own application, with a separate building load and supply-and-return temperature study.
Design the building and emitters together
In new construction, evaluate radiant floors or low-temperature radiators around the room loads and a cool return-water target. The manual provides a central-heating example with fan coils; the radiant and radiator pathways shown here are project concepts requiring emitter-specific design.
Air-to-water CO₂ (R744) heating system — user’s manual — p. 22
Return temperature changes the result
At 44.6°F (7°C) outdoor air and a 131°F (55°C) outlet, the supplied table lists 127.4 kW and COP 4.28 with a 50°F (10°C) inlet, versus 90.5 kW and COP 2.45 with a 104°F (40°C) inlet. A warmer-return heating circuit cannot inherit the cold-inlet DHW figure.
AEHCO2/125 performance table — p. 1
A cool-return design target
For this offering, target 68–77°F (20–25°C) at the heat-pump inlet/return. That target is not automatically achieved by calling an emitter “low temperature.” Select and verify its output, flow and return temperature at the design load. Secondary mixing does not by itself guarantee a cold heat-pump return.
AEHCO2/125 performance table
Keep heating water and potable water distinct
P10 depicts a closed heating-water concept with storage and a secondary circulation loop. It is not connected to the DHW taps. If one plant serves both duties, define separation, load priority and recovery explicitly before claiming simultaneous service.
Air-to-water CO₂ (R744) heating system — user’s manual — pp. 21-22
This heating pathway is for new construction. Below a 113°F (45°C) heat-pump outlet, the supplied table does not provide performance values; any lower-temperature secondary emitter loop needs its own design.
Information to prepare for your hot-water review: Room-by-room heating loads; emitter schedule; design supply/return temperatures; outdoor design condition; operating schedule; water/glycol specification if proposed; DHW priority.
Turn your assumptions into a first project brief. Explore a preliminary estimate, then prepare the information for a technical review.
Dalrada: the product documentation
Dalrada publishes the DCE-125 product literature. The review should identify the applicable model revision and obtain its current performance, installation and electrical submittals before the project advances.
ATI and Dalrada announced a distribution agreement in August 2024. ATI describes design and specification assistance among its consulting services. The precise supply, installation, commissioning and maintenance scope for your project will be defined in the proposal.
ATI — Dalrada distribution agreement announcement · ATI — Consulting services
Prepare a useful first review
Organize the building brief, measured or estimated demand, existing-system information and site constraints. Separate facts from assumptions so the team can identify missing information and the next engineering decision.
What happens next
The proposed study workflow is: review the inputs, identify an application concept, check equipment and site compatibility, then define the detailed engineering scope. A preliminary result is not a stamped design, firm quotation or compliance certificate.
The project proposal defines the supply, engineering, installation, commissioning and ongoing service responsibilities.
Information to prepare for your hot-water review: Company and project contact; building brief; available technical documents; desired decision date; who is responsible for the building’s engineering.
Prepare a first technical brief. Known values, estimates and unknowns should be clearly identified so the initial assumptions can be reviewed.
Your project workspace
Open the studio after the ATI introduction, without an account or sign-in link. Replace the example inputs with your project conditions, calculate a preliminary balance, then keep a readable summary for technical review. Nothing is sent automatically.
Define the hot-water requirement
Enter daily volume and units, and state whether it is measured at the fixture or at the storage/production temperature. Add cold-water inlet, delivery and production temperatures, recovery hours and the peak-period profile. Leave unknown values identified in the project brief; a numerical result requires the essential inputs.
Describe the operating conditions
Provide the outdoor design temperature and its source, rather than today’s weather. Add recirculation conditions, storage information, available electrical supply, proposed location and whether backup must remain. Heating projects also need a separate load and emitter schedule.
AEHCO2/125 performance table · Air-to-water CO₂ (R744) heating system — user’s manual — pp. 16-28
What the preliminary result can show
A first assessment can summarize the thermal duty, recovery window, available documented performance points and missing inputs. It must label assumptions and distinguish equipment power from whole-system electricity use. Equipment count, storage selection and compliance outcomes require further validation.
A transparent thermal calculation
For water, an initial energy estimate is Q ≈ 0.001163 × V × (Ttarget − Tcold), with Q in kWh, V in liters and temperatures in °C, before losses. Recovery duty is Q divided by the available hours. This is a water-heating balance, not a heat-pump selection or a space-heating load calculation.
Air-to-water CO₂ (R744) heating system — user’s manual — p. 9 energy-balance principle
The studio uses the supplied performance table within its available conditions. It does not establish equipment selection, annual savings or LL97 compliance. Inputs and results stay in page memory; download the summary before reloading or closing.
Information to prepare for your hot-water review: Prepare a demand profile, schematic, equipment nameplates, plant/roof photos, electrical one-line, plans and utility data for the project review. Explain which values were measured, estimated or supplied by others. This studio does not upload or send these documents.
Explore hot-water applications for laundries, fitness clubs and aquatic centers.
Commercial laundries
Repeated wash cycles. Overlapping fills. Plan hot-water production and storage around the way your laundry works.
Start with the cycle
Record hot-water gallons per cycle, required inlet temperature and the machines filling at the same time. A daily total alone cannot describe a short demand peak.
Plan production and storage together
Storage can bridge short peaks when enough energy is available. It cannot make up for an ongoing daily production deficit.
Confirm the process
Check equipment requirements, water quality, available power and connection points. Process water and domestic hot water may have different requirements.
Information to prepare for your hot-water review: Machine schedules, hot-water gallons per cycle, simultaneous fills, cold-water and supply temperatures, operating hours and existing equipment.
The Dalrada DCE 125 CO₂ air-to-water heat pump produces hot water for commercial applications. Its suitability for your laundry must be confirmed for your operating conditions. The calculation tools support a preliminary review of daily energy needs; a separate assessment is required to evaluate short demand peaks when multiple machines fill simultaneously.
The busiest class ends. The showers fill. Understand the peak, usable storage and recovery before the next busy period.
Follow the busy period
Start with simultaneous showers, flow rates, duration and class finishing times. Assess daily energy and the timing of peaks separately.
Separate delivery and storage
Define shower delivery, stored-water and incoming cold-water temperatures before comparing demand with production.
Study the complete system
Distribution, recirculation, temperature control and water hygiene require project-specific review. A warm recirculation return is not automatically a suitable direct heat-pump return.
Information to prepare for your hot-water review: Shower count, US gal/min, use duration, simultaneous users, class timetable, water temperatures, storage and recirculation details.
The calculation tools provide a preliminary review of domestic hot-water needs. Final system selection, water hygiene and distribution design require project-specific technical review.
Look beyond the surface. Showers and changing rooms need domestic hot water; heating the pool is a separate engineering study.
Showers and changing rooms
Assess domestic hot water (DHW) from visitor patterns, shower flows and peak periods, including storage, recovery and distribution.
Study the pool separately
Pool dimensions, target water temperature, covers and operating hours matter. Indoor air temperature, humidity and ventilation also affect the assessment.
Confirm equipment suitability
Pool-water chemistry, heat exchangers and hydraulic separation must be evaluated. This illustration does not establish DCE 125 suitability for heating the pool water.
Information to prepare for your hot-water review: For showers: visitor schedules, flows and temperatures. For a pool study: dimensions, indoor/outdoor location, target temperature, cover schedule and existing heating.
Use of the Dalrada DCE 125 CO₂ air-to-water heat pump for pool heating requires a separate technical assessment. The current DHW calculator covers showers and changing rooms only. Pool-heating calculations and sizing require a separate technical review.
