How To Size A Variable Speed Heat Pump

Sizing an Air-Source Heat Pump

I need assist with air-source oestrus pump sizing.

My business firm is one,870 sq ft ranch business firm with a 900 sq ft finished basement. The house is located in Westchester County, NY. The basement air is already conditioned with a 1-Ton ductless mini-split up heat pump. I'chiliad looking to replace the 50-yr quondam key AC for the chief level. The house has gas-based hydronic heating with baseboards. The gas boiler is a 120,000 BTU/Hr System2000 EK-i boiler. It seems highly oversized for the firm. The system cycles a lot and the temperature variation is quite high.

To increase the comfort level (proceed the temperature steadier), I'm leaning towards using a heat pump to both absurd and heat the business firm. In the winters, I would use the heat pump as the primary source of heat and when the outdoor temperature falls too low for the oestrus pump to handle, use the hydronic system as the secondary estrus source. In the summers, the heat pump would be the but source of cooling.

I had a professional run Manual J and Transmission D calculations for me. The Manual J report is attached. It shows total cooling required as about 30,000 Btuh and total heating required at about 47,000 Btuh. I want to become with a variable speed system in order to keep the indoor temperature written report. I take narrowed downwards to the Carrier Infinity Greenspeed 25VNA4 series heat pump coupled with a Carrier FE4ANB005L air handler. My HVAC contractor is recommending the 4-Ton 25VNA448 heat pump (specs can be found at https://ashp.neep.org/#!/product/32814 and https://www.shareddocs.com/hvac/docs/1009/Public/06/25VNA4-02PD.pdf). This is an overkill for summer months but meets the wintertime heating requirement.

My question for the experts:

1. Should I go with a 3-Ton 25VNA436 or the 4-Ton 25VNA448 heat pump? 3-Ton would be more than adequate for the summers. Given that I accept reliable (though oversized) secondary oestrus source, would I be fine with a 3-Ton oestrus pump in the winters? One schoolhouse of thought says to but purchase what is needed for heating and let the heat pump adjust speed downwards to see the bottom summer load. Does the fact that I take a reliable secondary source of rut impact this rationale?

2. Are at that place published efficiency figures on the variable speed oestrus pumps running at 25 or 50% of capacity? Without the efficiency ratings at low speeds, I don't know whether a four-Ton unit would be every bit efficient in the summers as a three-Ton unit.

3. Would I have to wire the heat pump controls to the banality controller or would it suffice to use thermostat settings to make the heat pump the chief heat source. E.thou., I could set the rut pump thermostat to seventy degrees and the boiler thermostat to 65 degrees. Would that work?

I would profoundly appreciate any input.