I work on a website – http://www.degreedays.net/ – that automatically generates heating and cooling degree days to any base temperature.

It should save you some hassle and give you more accurate figures in the future. Hope you find it useful!

Just curious – did you calculate actual heating and cooling loads considering the row-house/party wall construction? Living through a gut rehab of my own rowhouse, the party walls create quite a consistent atmosphere – even in the extreme Chicago winter months the interior never dropped below 48 degrees in the untempered portions of the house – or above 82 in cooling seasons. Though, I have joked that completion of our home may help out the neighbors utility bills .

Best option seems to be to double the ventilation rate (to say 60 cu.m/hr versus 30 cu.m/hr) to transport twice the “coolth” for the same temperature drop. In summer this increased air flow may also aid comfort. On the down side it means higher power consumption by the ventilation fans and more fan noise. Also means the HRV/ERV needs to have twice the capacity in summer than it does in winter and would be more expensive to acquire and operate. However,the higher flow rate only needs to be used when the outside temperature warrants it.

I have designed a belvedere with a cupola on top in the center of the roof to function as a solar chimney to passively pull air through the house. I have designed a “passive cooling” and “active dehumidification” chamber in the north side basement of the house to condition incoming air. Fresh air can enter from basement well windows heavily shaded by the foundation plants on the cooler north side of the house be dehumidified in the conditioning chamber and pulled through the house by the air rising and exiting out of the solar chimney (with all other windows in the house closed).

With cooler air entering the basement and hotter air exiting the roof belvedere, the higher moisture capacity of the exiting hot air should help further control humidity in the house (passive dehumidification). I also intend to install active ventillation systems in the bathrooms, kitchen, and laundry room to pull humidity and tainted air out of the house at the source, before it can circulate through the house.

I learned a lot when I looked into tying this active ventillation system into a whole house ERV… I didn’t think I would need an ERV with the passive airflow generated by the solar chimney and the basement dehumidification of the “replacement” air.. So I figured I would just actively vent the air in these rooms and have the replacement air come through the basement the same as the replacement air for the solar chimney.

However, with the higher number of cooling degree days in Alabama, I will likely need an active cooling system for at least one month of the year, plus the house will require active heating in the winter. On those days where the house is sealed tight, I expect the ventillation system and intake replacement air (required to maintain indoor air quality when the house is sealed for active conditioning — heating or cooling) will be a HUGE waste of energy without an ERV.

Studying PassivHaus design I have learned that very little energy is required to maintain a comfortable steady state in a super-insulated (effective R of over 50) sealed house with limited interior thermal loads and which has an active ERV and dehumidification system. In fact, such a “tight” and energy efficient PassivHaus design utilizing an ERV with a dehumidifier, essentially makes passive cooling techniques, passive ventillation design, and thermal mass benefits redundant at best and likely useless since it ends up cheaper just to leave the house closed and allow the active systems to continuously operate… I have come to the conclusion that the best overall bang for the buck when it comes to energy efficiency and comfort is to invest in a tight, super-insulated envelope with an efficient ERV and dehumidification system.

After following PassivHaus design principles, a relatively inexpensive, (even energy-inefficient) supplemental cooling system will provide the only additional cooling you might ever need, if any, at a MUCH LOWER operating cost than even a highly-energy efficient multi-stage geothermal heat pump can when it is trying to cool and dehumidify a house that is bringing in fresh replacement air without an ERV/dehumidifier!

Thus, after I have put enormous effort into a very effective “passive” design to save energy, the heating and active cooling months which require a “sealed house” are ultimately forcing me towards an active ERV and dehumidification system and a super-insulated always closed “tight envelope” as my most energy efficient option!

With so many heating days in Pennsylvania requiring a “tightly closed” but well ventillated home, the ERV makes perfect sense. Just keep the house “closed” year round and let the ERV maintain a year-round “steady state.” Limit the heat energy from appliances and fixtures inside the tight envelope (low heat lighting, convection cook top, laundry in the garage outside of the ERV conditioned envelope, etc.), and allow the ERV to help cost-effectively maintain a year round “steady-state.” If you do this, you likely won’t need an active cooling system in Pennsylvania.

I will likely still need some active cooling down here in northern Alabama. But the radiant floor system used for heating my home can also be used to circulate a cool fluid during the summer to pull some additional heat out of the home. Properly designed, the solar hot water heaters (used to heat the raidant floor as well as the hot water) can do an excellent job at cooling fluids during the night time, and thereby dumping heat from my home over night! I will use high thermal mass to prevent temperature swings from occuring during the day and the night and across seasons, and to thereby allow the ERV to be even more efficient at maintaining a “steady state.”

Anyway, I’ve been deeply researching similar concepts as you and this is some of my thoughts so far. I look forward to hearing how your project turns out and learning from your experience. I likely won’t begin construction for about 18 months.

In addition to the scientific analysis, it helps to actually “live it” for a while, since personal comfort levels differ between individuals. The computer model cannot generate a number to quantify your “coolness” when you are lying naked on top of the covers with the ceiling fan on. By the way, that scenario should work all the time, and if it’s OK with the homeowner, then A/C is unnecessary.

My answer to the question is no, and there are two issues working against you.

1. Personal comfort is the intent here. A/C systems are designed to deliver personal comfort. Dehumidifiers are designed for a slightly different goal, which is drier indoor air.

2. During those two hot months, the nighttime temperature doesn’t always drop far enough to get the house to say, 76F by morning.