FAQ
Everything you need to know about all-season heat pumps.
AReCoS was founded in 2023 to make heat pumps a real choice in every season: heating that keeps going in the cold, without handing the building back to gas or resistance heat.
Company
Who we are.
When was AReCoS founded?
2023, to solve one problem: most air-source units stop to defrost and hand the heating to gas or resistance strips.
What does AReCoS make?
First, an all-season heat pump rooftop unit for light commercial buildings, up to 10 tons; next, a residential size, up to 5 tons. AReCoS also supplies and licenses the embedded controller for commercial and industrial refrigeration, and an EV heat pump and controller (vehicles).
How does AReCoS make money?
Four ways: heat pump unit sales; for selected customers, a share of verified energy savings; the refrigeration controller, supplied and licensed; and vehicle thermal systems.
More detail
The savings share is planned to be verified against a measured baseline by IPMVP methods, on terms set with each pilot site, and to need no added sensors, gateways or cloud optimization.
Operators buy the controller; manufacturers that build it in license it per unit, plus integration fees. Vehicle pilots are planned to get the EV heat pump and controller as one package; production programs are planned to license the control software per vehicle, plus integration fees.
Who does AReCoS serve?
The heat pumps: building owners and managers, HVAC contractors, distributors and utility efficiency programs, with equipment manufacturers as partners for the first builds. The controller: commercial and industrial refrigeration operators and the manufacturers that build those systems. The EV heat pump and control software: automakers and their vehicle programs.
What stands behind the technology?
Two things. The embedded controller is U.S. Patent 12,768,557, issued October 20, 2026, from application 18/592,624; the air–water heat exchanger is patent pending, on a U.S. provisional application.
We are now testing the controller with Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC for the U.S. Department of Energy (DOE), for rooftop-unit energy optimization, under a Cooperative Research and Development Agreement with UT-Battelle supported by the DOE, from October 2025 to April 2027.
More detail
A hardware test in the published application, FIGS. 4–7, shows the controller running a vapor-compression system in cooling from temperature sensors only, setting its compressor, electronic expansion valve, air blower and fan together.
What stage is the technology at?
The controller is available for evaluation today on commercial and industrial refrigeration systems, and in testing with ORNL through April 2027. The heat pumps are in design and development, with pilots planned from 2027.
More detail
The rooftop unit is in design with the air–water heat exchanger; chamber testing at the AHRI frost point precedes pilot units in 2027 and commercial units, targeted for 2028. The EV and residential heat pumps are in development on the same controller and heat exchanger (dates).
Who leads the company?
Ahmed Hussein, PhD, founder and CEO, invented the embedded controller and the air–water heat exchanger. Ahmed Atallah, PhD, is the physics modeling lead. More about the founder.
The heat pump RTU
How it works.
What is the AReCoS all-season heat pump RTU?
An air-source heat pump rooftop unit with the AReCoS embedded controller on board, designed to heat in winter and cool in summer. Its air–water heat exchanger is designed to keep frost to a thin layer the unit clears while it keeps heating.
Why does frost matter so much?
Frost on the outdoor coil, most often near freezing in humid weather, makes most air-source heat pumps reverse and stop heating to defrost, handing the building to resistance strips or a gas furnace. The AReCoS unit is designed to keep heating without a conventional reverse-cycle defrost stop.
In 311 UK homes measured over a year and a half, heat pumps on days averaging just above freezing reversed about ten times a day, about four minutes each, and took back about 5% of the heat they delivered; on days around 48 °F (9 °C), under 1%.1
1. OpenEnergyMonitor, heatpumpmonitor.org, open data downloaded October 24, 2026, used under CC BY 4.0. AReCoS selected 311 air-to-water systems with certified meters and grouped their daily data for October 2024 to March 2026 by outdoor temperature: heat taken back is the heat drawn from the heating water, as the site’s statistics record it, and the 10-second sample covers 195 near-freezing days on 39 systems. Homes heated through radiator water, not rooftop units. OpenEnergyMonitor is not affiliated with AReCoS.
What is the air–water heat exchanger?
The patent-pending outdoor heat exchanger of the AReCoS heat pump: a pumped water–antifreeze loop around the outdoor refrigerant coil. The heat still comes from the outdoor air.
The loop carries heat from the air to the refrigerant in winter, with the coil as the evaporator, and the refrigerant's heat out to the air in summer, with the coil as the condenser.
- Hot refrigerant
- Cold refrigerant
- Water–antifreeze loop
- Sensor
- AReCoS embedded controller designed to set compressor · reversing valve · EXV · fan · blower · water pump together
How does it keep heating without stopping to defrost?
Instead of letting frost build and then stopping to melt it, a new electromechanical system is designed to limit frost to a thin, controlled layer and clear it continuously while the unit keeps heating. If it faults, the unit is designed to fall back to standard defrost and report it.
The frost-clearing technique and its test plan are available to manufacturers and investors under NDA: request the technical brief.
More detail
The water–antifreeze loop is designed to be sealed and freeze-protected, including after a ground loop is connected, needing only pump and antifreeze checks at routine service.
How cold can it keep heating?
The rooftop unit is designed to deliver 100% of its 47 °F rated heating capacity at 0 °F (−18 °C), and at least 70% of it at −15 °F (−26 °C): for the 10-ton unit, about 120,000 Btu/h at both 47 °F and 0 °F, and at least 84,000 Btu/h at −15 °F. The residential unit targets at least 70% at 0 °F. Beyond that, backup heat.
More detail
The residential unit trades some low-temperature capacity for seasonal efficiency; the rooftop unit uses a wider-range compressor for commercial heating loads.
Do I still need electric heat strips or a backup furnace?
Not for everyday heat. The rooftop unit is designed to carry the load down to 0 °F without defrost stops, so electric backup is optional, for emergency heat and loads beyond its capacity (how cold); a home in a very cold climate may keep a small electric backup for the coldest hours. No gas backup is required, but in a home pilot an existing gas furnace is planned to stay in place as a backup, so the home stays heated if the heat pump needs service.
More detail
Electric backup is offered at 10, 15 or 20 kW on the 10-ton unit, designed to lock out on request.
Rooftop-unit sites that want gas can add an optional gas heat section from the first commercial units in 2028; the heat pump leads, gas carries what it cannot, and the unit is designed to switch between electric and gas heat on request. On a dual-fuel unit, the controller is designed to decide the switchover itself, from outdoor temperature, the heat pump’s available capacity and its frost state, or on a price, emissions or grid request, inside limits set at commissioning. Pilot units are all-electric.
What happens to defrost and backup heat during a grid event?
In normal operation the unit is designed to need no reverse-cycle defrost, so there is no defrost to schedule and no backup-heat spike with it. If the frost-clearing system faults, its fallback defrost is designed to start early or wait on request, inside the coil's frost limit.
More detail
Conventional units tend to defrost in the same damp hours near freezing, and the backup heat that tempers each defrost can stack into a peak. On this unit, backup heat is designed to lock out on request (backup options).
What efficiency is it designed for?
Rooftop unit: IEER 22.1 and EER 13.4, with COP 3.72 at 47 °F and 2.57 at 17 °F. Residential unit: SEER2 23.8 and HSPF2 10.9. These are prototype design estimates at standard rating conditions, with the AReCoS controller, to be updated during certification; the methodology is available under NDA.
How much carbon does a unit avoid?
About 2 to 3 tonnes CO2e a year per 10-ton unit in a Minneapolis building: an estimate, not a measured result, from the 5,000 to 8,000 kWh a year it is designed to save.
Across a thousand units, that is 2,000 to 3,000 tonnes a year: more where a gas furnace carries the cold hours today, less on a cleaner grid, more on a coal-heavy one.
More detail: how it is estimated
By Minnesota’s method for estimating utility-program savings, a conventional 10-ton heat pump rooftop unit at the federal minimum efficiency uses about 20,000 to 25,000 kWh a year for heating and cooling there.2 Using 15 to 20% less energy than that unit saves about 3,000 to 5,000 kWh; heating through the cold without leaning on resistance backup is designed to avoid roughly 2,000 to 3,000 kWh more.
The design ratings alone account for about 14 to 17% less energy; the rest of the 15 to 20% is designed to come from heating without defrost cycles, which the 47 °F rating behind that baseline leaves out.
The tonnes are at the U.S. average grid intensity, about 0.35 kg CO2e per kWh (EPA eGRID2023).3 AReCoS is working this up into attributable tCO2e per unit per year and at fleet scale (method and assumptions under NDA), and will update these numbers with measured data during unit certification.
2. State of Minnesota, Technical Reference Manual for Energy Conservation Optimization Programs, Version 5.0, 2026, measure 2.02.10, Tables 1–3, pp. 380–381. A code-minimum baseline of IEER 14.1 and COP 3.4, at the full-load hours for Minneapolis–St. Paul: about 19,000 to 24,000 kWh for most building types, from about 17,000 (manufacturing) to 32,000 (hospital) across all sixteen, and about 20,500 for a low-rise office. Excludes resistance backup.
3. U.S. Environmental Protection Agency, eGRID2023 Summary Tables (Rev 2), June 2025: U.S. total output emission rate, 770.9 lb CO2e per MWh.
What does "ground-ready" mean?
The unit runs as an air-source heat pump from day one, and its water loop is designed to connect externally to a ground loop later, when the owner is ready, without replacing the unit: no ground loop to pay for up front, and the option kept. Once a loop is connected, the controller is designed to draw each hour on the warmer of outdoor air and loop fluid, through the same antifreeze circuit, with gas, where fitted, for the coldest hours.
What refrigerant does it use?
R-454B, an A2L refrigerant, with a global warming potential (GWP) of 465 by EPA’s method, below the limit of 700 that EPA’s Technology Transitions rule under the AIM Act sets for new air conditioners and heat pumps in buildings.4 Units for the UK and Europe are planned with a low-GWP refrigerant (UK and European units).
More detail
Other published values, 466 to 531, use other reference data (IPCC assessment reports AR4 to AR6). Both units are designed to carry a refrigerant detection system and leak mitigation to UL 60335-2-40.
4. U.S. Environmental Protection Agency, Phasedown of Hydrofluorocarbons: Restrictions on the Use of Certain Hydrofluorocarbons under Subsection (i) of the AIM Act, final rule, October 2023.
Which standards is it designed for?
It is designed to be safety-listed to UL 60335-2-40, rated to AHRI 340/360 (AHRI 210/240 below 65,000 Btu/h), and to the U.S. DOE and ASHRAE 90.1 minimum efficiencies.
More detail: other standards
- AHRI 1340, with IVEC and IVHE, when required.
- Refrigerant safety to ASHRAE 15, for an A2L refrigerant classed under ASHRAE 34.
- BACnet (ASHRAE 135) at the building interface.
- With its controller and optional cloud monitoring, it is also designed to the EU Cyber Resilience Act’s essential cybersecurity requirements.
- The residential unit is designed for UL 60335-2-40 listing and AHRI 210/240 ratings.
Does it cool in extreme heat?
Yes: it is designed to keep cooling up to 115 °F.
Does it need a cloud connection or a smart supervisor?
No. The embedded controller is designed to optimize each unit on the unit itself; units on one site share the load and agree their best operating setpoints among themselves over the local network or BACnet, within the building's comfort limits. The cloud is optional, for monitoring only, with no internet link in the control path.
A building automation system, where there is one, keeps the goals: setpoints, schedules and demand response.
More detail: supervisors, and a field test
Several rooftop units, each on its own thermostat, usually need a smart supervisory system to coordinate them, often with a yearly cloud subscription: a second system to install, integrate and keep paying for. One that only writes setpoints can tell a unit what to aim for and when to run, not set its compressor, valve, fans and pump together, and its cost weighs against its savings.
In a national-laboratory field test of advanced rooftop-unit controls on eight buildings, adding a remote monitoring package to the controllers raised the average payback per site from 2.3 to 4.4 years; at the one single-unit site, from 3 years to 10, and at the lowest electricity price tested it never paid back. More units per site shrink that penalty per unit.5
5. W. Wang et al., Advanced Rooftop Control (ARC) Retrofit: Field-Test Results, PNNL-22656, Pacific Northwest National Laboratory, July 2013, section 8.2 and Tables 23 and 24. Paybacks at the highest of the three electricity prices in the report. That package recorded performance for the test and did not control the units.
Could someone hack the cloud and take over the heating and cooling?
The AReCoS cloud is designed so it can’t: it only monitors. Every command is designed to stay inside the units, so no AReCoS service online can command them, and optimizing continues with the internet down.
Firmware is designed to be updated only on site, never through the cloud, and each controller is designed to install it only after checking AReCoS’s signature itself (security).
More detail: official guidance, the network and the firmware
Keeping commands inside the units covers the optimizer and every command to your equipment: setpoints, starting and stopping, sharing the load. The cloud is optional, for your visibility and data collection, and monitoring can stay offline at the store or building.
Official guidance agrees. NIST warns that the risk of cyberattack on building controls increases significantly
as they join corporate networks and the cloud.6 CISA, the FBI, EPA and DOE put removing control systems’ connections to the public internet first of five steps.7 DOE’s technology reviews name unintended access points
among the concerns when controls join a building’s network.8
Your building’s own network still needs protecting: AReCoS plans BACnet Secure Connect, which encrypts and authenticates the link between units. The controllers and rooftop heat pump are being designed to the EU Cyber Resilience Act’s essential cybersecurity requirements; the security page says how, and how to report a flaw to AReCoS.
6. NIST, NIST Releases Tips & Tactics for Building Automation & Control System Cybersecurity, Cybersecurity Insights, August 19, 2026.
7. CISA, FBI, EPA and DOE, Primary Mitigations to Reduce Cyber Threats to Operational Technology, May 6, 2025.
8. U.S. Department of Energy, Building Technologies Office, High Impact Technology Catalyst: 2017 Prioritization Analysis, October 2017, Table 12, barrier 8, p. 12, Security concerns
.
Can it respond to the grid?
Yes, as part of its own optimization rather than as an override: it is designed to shed 15% of its power on request and 40% in a critical event, and to add 15% when the grid has power to spare, winter and summer.
The controller is designed to shed what the building will miss least, backup heat before compressor speed, with the fans and pump rebalanced, and to store heat or cold ahead of a peak, coast through it and pace the recovery.
More detail
A thermostat, the building automation system, an aggregator or the utility can ask for a setpoint or an offset, a kW cap, or a cut or increase in percent or kW, as a value or a level (how requests arrive).
Its controller is designed to model the machine and learn how fast the building warms and cools, so the rebound sets no new peak, warming up earlier in winter on the heat pump, not late on backup heat.
It is designed to say how long it can hold and report what it delivered against what it would have drawn. Programs often set a minimum load per enrollment, so a building usually enrolls its units together or through an aggregator.
Can the utility or an aggregator take control of my units?
No. The grid can ask; the controller decides how. Each request is designed to be answered inside comfort and equipment limits set at the unit, which no request can change.
Levels map to limits you set at commissioning, and emergency heat and the building's low-temperature limit are designed to keep priority. At a limit, the unit is designed to end its part and report it (no AReCoS service can command your units).
More detail: how requests arrive
Requests are designed to arrive by OpenADR 2.0b at your building automation system or a gateway and reach the units over your own wired Ethernet network (IEEE 802.3), or by IEEE 2030.5 through a gateway that translates it. Without a building system, a grid-ready thermostat wired to the unit is designed to carry setpoint-shift and pre-heat or pre-cool requests. The unit has no Wi-Fi or Zigbee radio.
Over BACnet on the local network, the unit is designed to take a setpoint or offset, a kW cap, a cut or add in percent or kW, shed levels, pre-heat and pre-cool, a defrost request or delay, backup lock-out and, on dual-fuel units, fuel select.
The residential unit is designed to take OpenADR or IEEE 2030.5 through a connected thermostat or gateway, with capacity cap, setpoint shift and pre-heat modes.
Owners, contractors and utilities
Owning, installing and verifying it.
Why reserve now?
The first units are limited, and the reservation list decides where they go. Reserving is free, with no obligation.
Holders hear first about pricing, configurations and schedules, and early sites can shape the first builds, with most of the first pilots’ cost planned to be covered (pilot cost).
What will a pilot cost us?
For the first pilot sites, AReCoS plans to cover most of the pilot’s cost. Places are limited and offered in reservation order. What a site would pay, if anything, is agreed with it before the pilot starts.
What will it cost, and what will it save?
Pricing is being set with manufacturing partners and will be shared with reservation holders before the first units are scheduled.
For a 10-ton rooftop unit in a Minneapolis building, savings are estimated at about 5,000 to 8,000 kWh a year, from higher efficiency and from heating without defrost cycles or resistance backup (how it is estimated). The embedded controller is designed to need no separate cloud subscription. Prototype estimates: efficiency.
Will it lower demand charges?
It is designed to. On an all-electric rooftop unit, one cold morning's warm-up on backup heat can set a month's demand charge; the AReCoS unit is designed to run that warm-up on the heat pump, starting earlier, and to hold a kW cap on the whole unit.
In a Minnesota field study, a 5-ton unit averaged over 25 kW on backup heat, against about 3.3 kW on its heat pump alone.9 Units on one meter are designed to share a site cap.
9. Center for Energy and Environment, Performance Report: Room & Board Heat Pump Rooftop Unit, Next Gen RTUs, v.20251203, p. 16.
More detail: how demand charges are set
A demand charge is usually set by the highest 15-minute average demand in the billing period; a national-laboratory survey of U.S. demand charges notes that such charges often make up 30 to 70% of a commercial electric bill.10 See also how cold it heats.
10. National Renewable Energy Laboratory, Identifying Potential Markets for Behind-the-Meter Battery Energy Storage: A Survey of U.S. Demand Charges, NREL/BR-6A20-68963, 2017, p. 2.
What about warranty, service and reliability?
The target for the first commercial units is an industry-standard commercial warranty, typically 1-year parts and 5-year compressor, with extended coverage planned.
Controller boards are planned to be stocked through distribution, and final terms, set with the manufacturing partners, will reach reservation holders before the first units ship.
The unit is designed around standard compressors, valves and fans from established suppliers and keeps its hard-wired safeties; its controller is designed as one replaceable board that screens every command against component limits before it is sent.
Will it replace my existing rooftop unit?
It is designed to replace light-commercial rooftop units up to 10 tons. Dimensions, curb options, weight and electrical requirements will be in the unit specification for the first builds. Contractors can reserve for a site now, and we will review its existing curb and electrical service with them.
How big an electrical circuit will it need?
A smaller one than an all-electric unit that leans on large resistance strips: backup is designed to be sized to the gap, not to defrost, and the 20 kW option draws 55.5 A at 208 V or 25.1 A at 460 V.
Carrying a 10-ton unit’s full 120,000 Btu/h on resistance would take 35.2 kW: 97.6 A at 208 V or 44.1 A at 460 V, three-phase.
More detail: supply, options and the coldest hours
Resistance strips are often the biggest load on a heat pump's circuit. The unit is planned for 208–230 V and 460 V three-phase, 575 V optional, with backup of none, 10, 15 or 20 kW, each the heat delivered at the unit's own supply voltage, not a 240 V nameplate figure that falls at 208 V (how cold it heats).
At −15 °F, where the heat pump is designed to deliver at least 84,000 Btu/h, 10 kW of backup would bring the unit back to about its full rated heating capacity. MCA and MOCP for each option will be in the unit specification.
For contractors: what will the specification cover?
The unit specification for the first builds will answer what a replacement job needs; the design basis set so far:
| Contractor concern | Design basis today |
|---|---|
| Existing curb | Replaces light-commercial rooftop units up to 10 tons; adapter curbs planned for common 7.5–10 ton footprints |
| Electrical | 208–230 V and 460 V three-phase, 575 V optional; designed for a smaller circuit, with backup, if any, sized to the gap, not to defrost (circuit) |
| Backup heat | Optional electric, up to 20 kW; optional gas heat section from 2028; pilot units all-electric (backup heat) |
| Refrigerant | R-454B (A2L); A2L service practices apply (refrigerant) |
| Diagnostics | On-unit fault codes, local service port, manual service mode; readings, charge history and fault flags over BACnet (diagnostics) |
| BAS | BACnet (ASHRAE 135), or a standard thermostat where there is no BAS; demand-response points and power read-backs in the points list |
| Grid | OpenADR 2.0b or IEEE 2030.5; no Wi-Fi or Zigbee radio (grid requests) |
| Warranty | Target: industry-standard commercial terms (warranty) |
More detail: data, carbon, training and parts
| Contractor concern | Design basis today |
|---|---|
| In the specification | Approximate unit weights and cabinet envelope, supply and return air configurations, economizer compatibility, MCA/MOCP |
| Point metadata | Designed to ship with Brick, ASHRAE 223P and Haystack metadata checked with BuildingMOTIF, so building controls find each setpoint, power, demand and fault point by name |
| Embodied carbon | A kg CO2e estimate by CIBSE TM65 North America, refrigerant included, designed to ship with the specification |
| Performance data | Designed to ship heating and cooling across the operating range, from the same model the controller carries, in ASHRAE 205 format wherever the standard has a specification for it |
| Training | AReCoS installer training program planned with the first units |
| Replacement parts | Standard compressors, valves and fans from established suppliers wherever possible |
How will contractors diagnose and service it?
The controller is designed to check every reading against a physics model of the unit and report each fault with its likely cause, where to look and when to act, most urgent first. No cloud is required.
With a building system, the diagnosis is designed to arrive over BACnet before anyone goes on the roof, naming a sticking valve, a failing fan, a bad sensor or a slow leak, so the likely part is on the first truck. With a standard thermostat, it is designed to show on the unit and at its local service port.
More detail: on the roof, and why today’s checks fall short
The residential unit is designed to report through a connected thermostat or gateway, so the technician arrives ready to fix it.
On the roof, a manual service mode is designed to let the technician run the compressor, expansion valve and fans within safe limits to confirm the diagnosis. After the repair, the controller is designed to check the work, including the new charge in heating and in cooling, so the owner knows the fix held.
A warm building is not proof of an efficient heat pump. In a year of measured data from 310 UK homes, the least efficient tenth, judged against their own water and outdoor temperatures, delivered a quarter less heat per kWh than the best tenth and kept rooms just as warm.11
Today's tools fall short: in nearly a thousand lab tests on rooftop units with other faults present, standard charge checks were right less than half the time, and a gauge hookup without low-loss fittings can let out about half a percent of the charge.12
11. OpenEnergyMonitor, heatpumpmonitor.org, open data downloaded October 24, 2026, used under CC BY 4.0. AReCoS selected 310 air-to-water systems with certified meters and a full year of data, ranked them by measured heat as a share of the ideal at their own temperatures, and compared the bottom and top tenths: COP 3.34 and 4.47, rooms 20.7 and 20.8 °C. UK homes, not rooftop units; the data does not say why a system is less efficient. OpenEnergyMonitor is not affiliated with AReCoS.
12. Robert Mowris & Associates, Laboratory Test Results of Commercial Packaged HVAC Maintenance Faults, for the California Public Utilities Commission, February 2016, pp. iii–iv: 992 tests of faults on four units, and 0.4 to 0.5% of the factory charge lost per hose hookup.
Will it catch a slow refrigerant leak?
It is designed to, in heating and in cooling, well before the unit struggles: the controller is designed to track the refrigerant in every mode and report how much is gone, how fast and since when.
The technician's leak detector still finds the joint, and the controller is designed to confirm the new charge after the repair. The refrigerant detection system stays the safety device, sensing refrigerant in the air; the controller is designed to track what is left in the circuit.
More detail: why a leak hides, and an example message
In lab tests, a rooftop unit a fifth short of charge lost about 3 percent of its efficiency, and at 30 percent short, a quarter.13 At rest, a circuit with any liquid left reads nearly the pressure of a full one, and in one study of fault data from over 28,000 monitored rooftop units, no monitoring watched the refrigerant circuit directly.14
13. U.S. Department of Energy, Building Technologies Office, High Impact Technology Catalyst: 2017 Prioritization Analysis, October 2017, Table 31, p. 36, from Southern California Edison laboratory tests.
14. G. Shoukas et al., Analysis of Fault Data Collected from Automated Fault Detection and Diagnostic Products for Packaged Rooftop Units, NREL/TP-5500-77077, National Renewable Energy Laboratory, September 2020, section 3.
RTU-3 · heating · 6:40 a.m.
Refrigerant charge falling. Act at the next visit, within two weeks.
About 7% below nameplate, falling about 1.5% a week for five weeks. No efficiency loss yet.
Ruled out: a sensor (both pressure sensors agreed at the last rest) and the weather (the shortfall holds at every outdoor temperature since it began).
Bring: an A2L-rated leak detector and R-454B.
Look at: the compressor lines, service ports, brazed joints, the coils and the refrigerant-to-water exchanger.
After the repair: weigh in the charge. The unit re-checks it in heating now, and in cooling at the next changeover.
Can it tell a bad sensor from a real fault?
Yes, that is what the physics is for: a loose or drifting sensor moves its own reading and breaks one of the model's checks, while a real fault moves the readings around it together, so the controller is designed to say which it is.
More detail
At rest, as the unit is designed to be at every changeover, its pressures equalize, so both pressure sensors must read the same and agree with the refrigerant's temperature; running, the refrigerant side and the air and water sides must carry the same heat.
Naming the sensor spares a wrong fix: in lab tests with other faults present, standard charge checks could call a correctly charged unit low, and adding refrigerant to it can cost efficiency (the lab tests).
Will it bury us in alarms?
It is designed not to. Findings are designed to arrive ranked: safety, then equipment damage, lost heating or cooling, then energy, each with a cost per day and a time to act, so a roof of 40 units reads as a short worklist. Ranking is designed never to hold back a safety alarm.
More detail: how a fault is raised, and the alarm count today
The controller is designed to raise a fault when the evidence clears the model's own margin of error, not when a timer runs out, to say when it cannot judge yet rather than guess, and to report a symptom once, at its cause. Findings show on the unit and over BACnet.
In one study of 317 buildings, fault tools reported a mean of 245 faults per building each month,15 too many to act on unranked.
15. Lawrence Berkeley National Laboratory, How Faulty are Commercial Buildings? HVAC Fault Prevalence Study Results, DOE Building Technologies Office Peer Review, 2023.
How will performance be verified?
Rated performance will come from certified testing: safety listing by a nationally recognized testing laboratory and ratings through an independent industry program. First pilot sites will be measured and verified against utility metering and the unit's own sensors, with results shared with host sites and program partners. Every pilot’s data is also planned to be public (how).
Will the performance data be public?
Yes. Every pilot and every home heat pump sold, anywhere in the world, is planned to ship with independent, open-source monitoring: certified, billing-grade meters for the electricity going in and, on air-to-water units, the heat coming out, logging continuously. AReCoS would rather be judged by measurements than by its own claims.
With each owner’s agreement, that data is planned to go live on heatpumpmonitor.org, the open, community-run record of how real heat pumps perform, side by side with every other system there. The community, not AReCoS, will be the judge.
More detail: meters, rooftop units and air-to-air
Pilot systems are planned with the MID-certified meters it asks of manufacturer-run systems. Anyone can read the data: owners, installers, utilities and competitors. Rooftop units are planned to publish their measured performance openly in the same way.
On air-to-water units the heat is metered directly. No open monitoring kit covers air-to-air heat pumps yet, so for those AReCoS plans to develop an open method, an energy balance across the unit’s internal water loop, checked in a test chamber, and to share it with the monitoring community.
For utilities and programs: how will pilots work?
Pilots are planned at cold-climate host sites in 2027 and 2028, with AReCoS supplying the unit and the metering, sharing 15-minute data with the program and verifying savings against a metered, weather-adjusted baseline.
DOE’s 2021 prioritization (preliminary, refined May 2021) ranked the cold-climate rooftop heat pump, as a technology category, 5th of 26 top technologies for commercial buildings.
More detail: data, verification and demand response
Data: unit power, heating and cooling delivered, backup-heat runtime and defrost events at 15-minute intervals. The same readings, with fault flags, are designed to be readable over BACnet and exportable to third-party monitoring and energy platforms, with no cloud required.
Measurement and verification: against the existing unit's metered, weather-adjusted baseline (IPMVP Option B), or a calibrated model (Option D) where there is none to meter.
Demand response: designed to answer OpenADR 2.0b requests with 15% and 40% sheds and a 15% load add, winter and summer (grid response, how requests arrive). Each unit is designed to report, from its model, the power it would have drawn without the request beside what it drew, for the site to check against the program's own baseline.
To discuss a pilot, email info@arecos.net.
How will the no-defrost claim be tested?
In a test chamber, at the AHRI heating rating and frost-accumulation points and down to the 0 °F and −15 °F targets, recording heating capacity, power, frost thickness on the outdoor heat exchanger and any interruption of heating. Results will be published with the first units' specification, and first pilot sites will report the same measurements over a full heating season.
More detail: the test points
The AHRI 340/360 heating rating points, 47 °F and 17 °F; the AHRI 210/240 frost-accumulation condition, 35 °F dry bulb and 33 °F wet bulb; then 5 °F, 0 °F and −15 °F.
Reserving and buying
Getting one of the first units.
When will the first units be available?
Targeted: rooftop pilot units in 2027 and commercial rooftop units in 2028; EV heat pump pilots with vehicle programs in summer–fall 2027; residential pilots in early 2028. International pilots are targeted from late summer 2027.
Pilots in the UK, Europe and other international markets depend on finalizing agreements with local manufacturing partners (outside the United States).
Can I reserve from outside the United States?
Yes. You can reserve a place from the UK, Europe or any other international market now, with no payment and no obligation. International pilots are targeted to begin in late summer 2027, depending on finalizing agreements with local manufacturing partners (UK and European units).
More detail
Those agreements will decide which products are piloted first in each country. AReCoS plans to build each country’s units with those partners and to have them certified to its own safety, refrigerant and efficiency requirements.
What will units for the UK and Europe be like?
An air-to-water home heat pump for radiators and underfloor heating, planned at about 3.5 to 17.6 kW (1 to 5 tons), and a light-commercial rooftop unit planned up to about 35 kW (10 tons), each with the same air–water heat exchanger and embedded controller, and refrigerant, electrical supply, ratings and marking set for each market.
Both are planned with a refrigerant below GWP 150 in the EU, Northern Ireland and Great Britain alike, so one design serves both markets; propane (R290) is the likely choice for the home unit.
More detail: supply, rules, ratings, grants and marking
- Electrical supply. Planned for 230 V single-phase and 400 V three-phase, 50 Hz, the same in the UK and the EU.
- Refrigerant, EU. Under F-gas Regulation (EU) 2024/573, self-contained (monobloc) heat pumps and air conditioners up to 50 kW that use a refrigerant with a GWP of 150 or more may not be placed on the EU market from 1 January 2027. Where safety requirements at the installation rule out a GWP below 150, the limit is 750.16
- Refrigerant, Great Britain. Great Britain has no GWP 150 limit for heat pumps in law; Northern Ireland follows the EU rule.
- Ratings, EU. Planned to be rated in kW to EN 14511, with seasonal efficiency (SCOP) to EN 14825. The home unit is planned to comply with Ecodesign Regulation 813/2013 and to carry the energy label under Regulation 811/2013. The rooftop unit is planned to comply with the Ecodesign rules for its class.
- Ratings, Great Britain. The same tests apply, under Great Britain’s own retained versions of those Ecodesign and labelling rules. Northern Ireland follows the EU versions.
- Grants, Great Britain. For homes, we plan certification under the Microgeneration Certification Scheme (MCS 007). The Boiler Upgrade Scheme in England and Wales needs MCS-certified products and an MCS-certified installer for its £7,500 grant.17 Scotland’s Home Energy Scotland grant needs MCS too.
- Safety standards. Designed to EN 378, the safety standard for the refrigerant system, and to EN IEC 60335-2-40, the safety standard for the appliance. The 2024 edition of that standard allows larger propane charges when added safety measures are in place.18
- Product marking. We plan CE marking for the EU. For Great Britain we plan UKCA, or CE, which Great Britain now accepts with no end date for these products.19
- Cybersecurity. The connected controller is planned to follow the EU’s cybersecurity rules for radio equipment and connected products. In the UK it is planned to follow the security rules for connectable consumer products.
- Noise for homes. In England, a heat pump installed without planning permission must be assessed by the MCS 020(a) method, and the result must be 42 dB(A) or less at the window of the nearest neighbour’s habitable room.20 The home unit is designed to that limit, and to national and local limits elsewhere in Europe.
16. European Commission, Climate-friendly alternatives to F-gases: air conditioning, accessed October 2026, online.
17. Ofgem, Boiler Upgrade Scheme, accessed October 2026, online.
18. Swiss Association for Standardization (SNV), SN EN IEC 60335-2-40:2024, accessed October 2026, online.
19. Fieldfisher, UK government extends the recognition of the CE mark in Great Britain indefinitely, accessed October 2026, online.
20. MCS, MCS has published an updated version of MCS 020, accessed October 2026, online.
How do I reserve a place?
Join the list with the reservation form. There is no payment and no obligation. We will contact you when the first units are scheduled; the list decides where they go.
Who builds the units?
AReCoS designs the unit, the controller and the air–water heat exchanger; the first units are planned to be built with a few established manufacturers.
Before sale in the United States, each model will be safety-listed by a nationally recognized testing laboratory and its performance certified through an independent industry rating program; before sale elsewhere, each model will be certified to that country’s own requirements.
Can contractors, distributors and utilities get involved now?
Yes. Contractors and distributors can reserve for their customers, building owners can offer to host one of the first units, and utility and efficiency programs are welcome to talk to us about pilots. Contact us.
The controller
One controller, many machines.
What does the AReCoS embedded controller do?
It is designed to run a physics model of the refrigerant cycle on the equipment, estimate what its sensors can't measure, and set the compressor, valves, fans and pumps together, not each actuator on its own loop.
A second model is designed to screen each command for likely component failures before it is sent. The physics model is also designed to name each fault's likely cause and where to look, and to count the refrigerant so a slow leak shows as a trend. See fault detection.
More detail: on the heat pump
- Startup and shutdown. Designed to bring the unit up without liquid floodback, and to track where the refrigerant settles as it stops, so the next start begins from a known state.
- Changeover. Designed to sequence the compressor, reversing valve and expansion valve through each switch between heating and cooling, moving the motor-driven reversing valve at rest, once the coil pressures have come together.
- Winter. Designed to need no reverse-cycle defrost in normal operation (how it clears frost).
What if my cases run thermostatic expansion valves?
Yes, around them: on a case that keeps its thermostatic valve, the controller is designed to set the compressors, fans and defrost while the valve runs on its own bulb. The full optimum needs an electronic expansion valve fitted in the retrofit. See what it replaces.
Can I use it on my own equipment?
Yes, on a commercial or industrial refrigeration system; for vehicles, see below. We supply the controller matched to the equipment, or license it per unit if you build the equipment, and it is designed to run standard components from different manufacturers. See the product brief.
Do you work with vehicles?
Yes. For pilots, the EV heat pump and controller are planned as one package, targeted for summer–fall 2027. For production, AReCoS plans to license the control software to run on the automaker's own thermal controller or in its supplier's heat pump module. EV heat pump and controller.
Still have a question?
Ask us about the heat pump, the first units, the controller or the EV heat pump.
Grand Rapids, Michigan 49546