First let me say that this forum is beyond amazing. That said, I have tried to find answers to my many question and was only able to find answers to a few. Here it goes.
I have a 1930's all brick two unit house in Yonkers, NY, but I'm only concerned with the first floor right now. That unit has 2 bedrooms, a kitchen, a bath, a living, dining, and sun rooms, which add up to around 1100 sq ft. The living, dining, and sun rooms were all gutted and redone last year (They were originally plastered). The exterior walls were insulated with R-5 foam board, while the ceiling was insulated with R-20 for sound proof reasons. The bedrooms, having been done two years earlier, were not gutted, but the walls were framed out and insulated with R-11. I also had a 4.2 kw solar system installed on the roof.
I have a Weil Mclain EG-55-P1 natural gas boiler heating the whole house through steam radiators, but there are no cooling equipment currently installed. Which brings me to my options. I am exploring the possibility of adding some sort of centralized cooling but since I'm going to be implementing that, I figured I might as well explore a possible heating upgrade.
Get a mini split heat pump system (Mitsubishi Mr. Slim) installed. This would be a four zone system. The sun room and the living room would be combined into one zone while the other rooms will each be on individual zones. However, this would mean that the air handlers would most likely be wall mounted, which are somewhat intrusive.
Install mini ducts with a high velocity (HV) air handler or a conventional duct and air handler with some sort of heat pump. This raises the question of whether HV ducts are a better choice than conventional ducts. Everything I read about HV ducts states that they are less efficient than conventional ducts. But what is a good estimate (%) of how less efficient it is? And what is the respective cost difference?
With regards to the heat pump, I was thinking of a geothermal or a standard air source unit. At first glance, the geothermal route increases the complexity if used with a HV air handler, which would increase cost. But the increased efficiency is extremely appealing. The other possibility, air source, suffers from decreased heat pump efficiency in winter temperatures near or below freezing. Which brings up the topic of cold climate heat pumps. The only models I came across are the Hallowell Acadia and the Mitsubishi Zubadan. I believe Hallowell is out of business and the Zubadan series is not available in the US. Are there any other models that would perform well in those temperatures?
Use a duct system, either HV or conventional, as a common distribution source. But instead of having a heat pump, I would use a separate unit for heating and another one for cooling. Obviously this means that I will have three pieces of equipment and would increase cost and possibly maintenance.
Something that I have not thought of yet.
I was able to calculate the heating and cooling loads using the HVAC-CALC software in accordance with Manual J. After factoring in some of the insulation I will me adding, the heat loss is 34700 BTUs while the heat gain is 19950 BTUs. If I were to get a heat pump, what size would it be? Do I use the cooling load BTUs and be short on the heating side, or do I use the heating load BTUs and be over sized on the cooling side?
I would like to use electricity as the energy source in order to utilize my solar system. I know this is a lot of information all at once. All your help and advice is greatly appreciated.