hvac appropriate for new 4 floors/units building in Brooklyn

gerold

We are tearing down a derelict building and rebuilding from scratch a 4 floor building with one 1300 sq foot 2 bedroom unit per floor. We will want central AC in addition to heat. What is the most sensible/efficient/construction cost effective approach to this situation? Roof and cellar are available for mechanicals as needed. We are inclined to have all separate systems. ALso hot water. Thanks for your input!

GMcD

Envelope

Design the best envelope you can with triple pane or better windows with exterior solar shading and reduce the loads as low as possible. Then you don't need very much heating or cooling in the first place, there will be better indoor comfort and quieter indoor conditions. Use a small HRV/ERV unit in each suite for individual control, maybe even small instantaneous wall hung individual boiler/water heaters with low temperature panel radiators with thermostatic control valves. Perhaps look at geo-exchange for cooling, or a conventional hydronic two-pipe heat pump circuit. There are packaged hydronic heat pump fan-coils with ERV sections for vertical closet installations that are good choices- I'm not at work right now so I can't get the link to some examples- very popular in Europe. Do a google search on these residential package AC/HRV/ERV units - very energy efficient. Here's one I found with a quick search:

http://www.ekocomfort.com/

Brad White

With all due respect to my Northern Compatriot

I take exception on one point: I would back away from the triple-pane window scenario and use good Low-E double-pane or historic sash with storms for at a few reasons:

1) Payback may be prolonged. 3-pane is expensive and often not cost effective in mid-latitude climates.

2) Thickness of muntins may not work if historic and can be ungainly (at least the ones I have seen) if you desire screens for summer operation. May not be of concern to you.

3) Triple-pane may thwart desired passive-solar gains. If you feel compelled to use triple-pane, reserve it for the north and north-east sides.

That said, the use of low-temperature HW and panel radiators is an excellent suggestion. The one drawback is capacity- If this is a row house with neighbors to either side, the heat losses can be rather small. This may not seem like a problem but it can result in oversized equipment because of what is commercially available. The upside is, your domestic hot water load becomes your largest heating requirement and any modulating-condensing (Mod-Con high efficiency) boiler can probably handle that with ease.

If masonry as I envision it might be, ICF's or insulated concrete forms may have a place. Dense wall insulation and high mass may allow passive or even active solar to thrive. Your ventilation load may be your largest heat loss as Geoff intimated. A heat recovery ventilator (HRV) can mitigate that well and provide a healthier indoor environment.

Heat pumps, even ductless split types may have a place here if the heating loads are low. These will provide AC as well of course.

I would secure the services of a competent architect or engineer to ascertain the heat loss, solar gains, general characteristics and features of which you can take advantage. Get accurate heat losses calculated too. Do that first. Without those, discussion of "real systems" is just hypothetical. Often "the loads dictate the system". Electric heat may even make an appearance (try not to gag, it has happened!).

It sounds like a fantastic opportunity to create a modern home (with perhaps an historic character?)!