arvono

I read your earlier post and meant to respond.

What were your design temperatures both cooling and heating and inside thermostat settings?

generally, you don't see air source heat pumps used often in Ma due to electric costs. any other heating fuel available?

small setbacks can be used successfully depending on your system's spare capacity. I use setbacks on my dual fuel system but I live in an area with moderate winters, totally different than yours.

If you do pursue HPs, then I would go two stg and oversize with a two ton system to get the extra heating BTUs. I would have someone review your load calcs especially on the heating side.

IMO

Hey Tigerdunes,

I used a winter design temp of 4F, a summer design temp of 88F and a thermostat setting of 72F. Two story colonial. 725 SF each floor. Closed cell spray foam.

In my area, we have oil, wood and in some areas natural gas. I could go with oil, but I like the idea of heat pumps. Currently, I'm thinking of air source or DX ground source.

Prior to getting the heating/cooling system, I'll have the contractor calc the loads...I just want to know what I should expect when they suggest something.

Just out of curiosity, why would you oversize a heating system? Or was that suggestion only for air source heat pumps in cold weather? Let's say I was going to go with an oil furnace, and I only needed 17,000 btu, would I also go with 2 tons or would 1.5 tons be sufficient.

Thanks in advance,

An air source heat pumps's output declines as the air temperature drops. There is a number you need to know about. It's called the COP, or coefficient of performance.

As the temperature drops, so does the COP. If the temperature gets low enough, the COP will drop to one. At that point there is no advantage to a heat pump over straight electric resistance heat.

You should review any candidate system's COP to get a feeling of just how much heat you will get when the temperatures are down there, especially in your locale.

Broadly speaking, air source heat pumps are not cost effective for heating in northern climates. Since you are going against that convention, you have a lot of homework to do to justify heating with a heat pump.

I wish you luck, but I suspect you will find that it makes more sense to heat with some other fuel and cool, if you really need to, with straight AC.

It's possible that you may find that it makes sense to buy a dual fuel heat pump, which switches to an alternative fuel when the temperature drops low enough and the heat pump starts to lose effectiveness. However, given the low temperatures in your area, even that may not be cost effective.

arvono

what size heat strip was recommended?

I am skeptical of your load calculation for heating.

Because of your home's tight construction, you probably should consider a fresh air ventilator and humidifier.

IMO

I don't remember the heat load program giving any recommendations regarding heat strips. Just heat gain and heat loss per floor, walls, ceiling, windows, doors, infiltration, etc. I had no idea how much was lost due to infiltration until I saw it calced.

A little skepticism is warranted as this is the first time I'm looking into heating and cooling loads.

However reasonable, I may have taken some shortcuts. The floor plans call for a 2 story building with a footprint of 26 ft by 30 ft and 8 ft ceilings. There's a garage underneath and a walk-up attic. Walls will be 2 x 6 construction. As only the first and second floors would be heated, I treated the house as a single room that would be 25 ft by 29 ft by 17 ft high (8+1+8). Then I added the windows, doors, and isulation r-values and used the programs recommended air change per hour for tight construction.

A ventilator and a dehumidifyer/humidifier sound like nice ideas.

The air source heat pump's conception resulted from the invention of air conditioning units. It was Willis Carrier, a mechanical engineering graduate who initially came up with the first drawings for an air conditioning unit in 1902. In 1914 Willis Carrier lost his job due to cut backs as World War 1 began. It was than that Carrier and seven fellow mechanical engineers set up their own company, the Carrier Engineering Corporation

The air conditioning units employed a 'refrigeration cycle' in order to produce cooler air, therefore de-humidifying and cooling the environment. Air source pumps adopt a similar process in reverse, therefore emitting heat instead of cooler air into the environment.

Theses pumpa are more commonly used in milder climates where temperatures are more consistent although there have been recent developments as in 2007 an Oklahoma inventor developed an ait to air heap pump defrosting system, allowing for their use in colder climates.

Here is a link that might be useful: Air Ventilators