Inside the Aris system

The outdoor unit charges an indoor hydronic loop and a stratified storage tank. Inside the home, water-temperature reset and modulating terminals deliver the comfort. Because the refrigerant circuit stays outdoors, there are no refrigerant line sets running through interior walls — the leak surface is dramatically smaller than a conventional ducted split or mini-split system.

The compressor is a variable-speed inverter that ramps continuously to match the home's instantaneous load instead of cycling on and off. Aris's control logic picks the lowest compressor speed whose capacity covers the current hourly load, because part-load operation is where heat pumps run most efficiently. Below the coldest tested outdoor temperature the performance is held constant rather than extrapolated — no fictional capacity claims.

The working refrigerant is R32, a single-component HFC with a global warming potential roughly a third of legacy R-410A and a clear regulatory path forward in the residential heat-pump category. A typical Aris install carries about 3 lb of R32 in the outdoor unit.

When the room loads briefly exceed the heat pump's capacity at extreme outdoor temperatures, an electric resistance element inside the thermal storage tank covers the shortfall. The element is the backup, not the workhorse — sized for tail conditions, not for daily duty.

Between the heat pump and the home sits a multi-chamber tank that combines two functions: domestic hot water (DHW) and thermal energy storage (TES) for space heating and cooling. The DHW chamber stores water hotter than the tap; a built-in mixing valve blends it with cold for delivery, so the usable supply is bigger than the tank's nominal volume. A standard 40-gallon configuration holds roughly four back-to-back standard showers' worth of hot water before the heat pump steps in to recover.

Recovery is fed by the full output of the home's heat pump, not the trickle from a small dedicated water-heater compressor. Back-to-back showers stay hot — the heat pump that warms the home in winter also pours energy into the tank between draws.

The TES side acts as a buffer between production and demand. When the heat pump produces more than the home needs, the surplus is stored as hot or cold water; when demand outpaces production, the home draws from the buffer. The result: the heat pump runs longer at its best-efficiency operating points instead of short-cycling to chase transients, and the system can shift load in time to take advantage of cleaner or cheaper grid hours.

The same tank hosts the electric backup element. When peak loads exceed heat-pump-only capacity, the element kicks in to cover the gap — and the hourly model tracks exactly how often that happens for your specific home and your specific weather.

Tight, well-insulated homes don't breathe on their own. Without a deliberate ventilation system you get stale bedroom air, moisture in the wrong places, and CO₂ levels that get in the way of good sleep. A balanced ERV moves air continuously and quietly in the background: fresh air to the rooms where people sleep and live, stale air pulled from the rooms where humidity and pollutants are generated (kitchens, bathrooms, laundry).

Per-room flows are designed against ASHRAE 62.2 with a 0.30 ACH reference, then validated with manufacturer-rated sensible-recovery data in the same hourly simulation that drives the rest of the design. Post-install commissioning verifies that the installed terminals actually move the airflow the design called for — not just that they exist.

An energy-recovery core transfers most of the heat from outgoing air into incoming air (and the reverse in summer). You get the indoor-air-quality benefits of generous outdoor-air exchange without throwing away the energy you've already paid to condition. The unit also handles the boost cases — cooking, showering — automatically, so there's no separate range-hood duct or bath fan to coordinate.

Filtration is MERV 13 on the incoming side, the residential rating that captures most fine particulates and a meaningful fraction of bioaerosols.

Water carries thousands of times more energy per cubic foot than air. We can move the same heating or cooling through PEX tubing that's a fraction of the diameter of equivalent ductwork, with much lower distribution losses and dramatically less noise. The system is broken into circuits sized per zone; the Hydro Control Unit dispatches flow and supply temperature to each zone independently.

At the room level, fan coil units (FCUs) deliver heating or cooling on demand. Each FCU is a small, quiet, low-voltage cabinet that pulls water from the hydronic loop and exchanges energy with room air through a coil and ECM fan. Microzoning is the default rather than the upgrade — every room gets its own coil and its own setpoint.

Radiant floors are available as an option for rooms where the architectural and comfort payoff is worth it. Most installs combine a few radiant zones with FCU-served rooms, which keeps the radiant cost contained while preserving the responsiveness FCUs give you for the rest of the home.

Cooling water leaves the heat pump in the high 40s°F with a dew-point margin built in, so un-insulated radiant tubing doesn't condense and FCUs run dry-coil whenever they can.

The Hydro Control Unit (HCU) is the indoor brain. It runs embedded firmware that handles real-time decisions — which circuits to open, what supply temperature to target, when to fire the heat pump, when to ramp the ERV — and talks back to an Aris-managed cloud service that handles longer-horizon orchestration.

The cloud side pulls weather forecasts, time-of-use electricity rates, and learned thermal data from the specific home, then plans the next several hours rather than reacting moment-to-moment. It decides when to pre-heat or pre-cool, when to charge the storage tank, and when to let the home coast on its own thermal mass.

Every Aris install gets over-the-air firmware updates: as the fleet teaches us, the improvements ship to every system automatically. Aris technicians see the same telemetry stream the homeowner sees; if something starts to drift, we usually notice before they do.

Traditional HVAC sizing uses Manual J: one outdoor design temperature, one indoor setpoint, multiply UA × ΔT per component, and pick equipment that covers the peak. It's a useful sanity check but it misses almost everything about how a home actually behaves through a year.

Aris sizes each install by running a full hourly building-energy simulation. Hourly weather comes from the TMYx dataset (Typical Meteorological Year, extended) compiled from 1999–2023 observations at the nearest weather station, with dry-bulb temperature, dew point, GHI/DNI/DHI solar radiation, wind speed, pressure, sky cover, and precipitation. The thermal solver models each room with a coupled three-node RC network (air, interior surface, structural mass) so heavy-mass walls actually behave like heavy-mass walls. Window solar gain is computed per orientation from the floor-plan azimuths and tempered by SHGC. Infiltration is modeled with a Sherman-Grimsrud wind/stack-effect formula driven by the hourly wind and indoor-outdoor ΔT.

Heat-pump capacity and COP at each hour are interpolated bilinearly across a performance grid built from third-party lab testing of the Aris heat pump — outdoor temperature, supply water temperature, and compressor speed. A second sub-hourly hydronic plant model steps within each hour to schedule time between space conditioning, DHW recovery, and tank standby; DHW priority events and defrost cycles show up in the hourly results.

The thermal engine is validated against ASHRAE Standard 140 (BESTEST) reference cases for low-mass and high-mass envelopes — annual heating and cooling totals fall within the reference range for cases 600, 610, 620, and 900. The conventional baselines (gas furnace, central AC, gas water heater) use the same hourly loads and weather, only the equipment differs.

After install, the same model produces the customer's performance report: predicted runtime, energy use, and comfort against the measured reality coming out of the system. Over time the model and the home converge.