Lately the team has been struggling a bit with the HVAC budget and design. The original budget was around $10K which is doable until we starting putting things like an HRV and solar thermal into our wish list. One of the questions we have been asking ourselves from the beginning is whether or not we need a traditional Air Conditioning system in the home at all?
Philadelphia’s summer’s are fairly mild and do not have a high number of cooling load requirement. I have a number in my notes that says we have a mean total cooling degree days of about 1,172 degrees F (with a reference of 70 degrees F). The vast majority of these CDD’s come between June and August (861) which means there are only three months out of the year that we can really make a good case for needing A/C in an average home in Philadelphia (source data).
The real issue we have in our area is really not heat, but humidity. Since the air is so much stickier here than other areas of the country, it feels much hotter than it often is during the summer. It is not as easy to cool our homes with passive cooling due to the high humidity levels as we will be bringing humid air into our homes.
So this brings us back to our original question - can we make a home comfortable during the summer is we employ simple passive cooling techniques in conjunction with a whole house dehumidification system? I think the answer is yes, but we are not 100% sure yet.
Let’s break this down into two parts here. A traditional air conditioning system will both cool and dehumidify the air in a home. We are simply breaking these two functions apart and handling the cooling requirement my mostly passive means, while employing a whole house dehumidifier for the dehumdification requirements.
Dehumidification
Let’s look at dehumidification first. The goal is to keep the humidity levels in the home below 50% ideally and 60% at the least. If we are successful in doing so, it has been proven that people are comfortable with their thermostats set between 78-80 degrees F during the summer. Since our baseline cooling degree days was calculated at 70 degrees, raising the target to ~79 degrees would drastically reduce and almost eliminate the total number of cooling degree days altogether. I don’t have the raw data to do this calculation officially, but there was a rough reduction of 600 cooling degree days for every 5 degrees added to the baseline from 55 to 70 degrees (source data).
The dehumidifier we are looking at is an Ultra-Aire 90H model that is capable of both dehumidifying the air as well as bringing in fresh air ventilation from outside (more on the ventilation benefits later). This model runs on a standard 110V outlet and only requires 6.3 Amps which means it should take much less power to run than a full A/C unit.
Passive (& some active) Cooling
Now for the cooling side. Here is a list of our cooling measures we are considering to employ in order to keep the inside temperature comfortable during the summer:
- Superior SIP Insulation - Keeps the house from getting hot and also remains a constant indoor temperature longer than a traditional home.
- Energy Star Windows - Low U values and proper glazing will help keep the home cooler.
- Cool Roof Coating - A white coating that will reflect more than 60% of the radiant heat from the sun.
- Landscape Shading - Trees in the back of the home will shade the south side and rear yard during the summer.
- Ivy Wall Covering - A wall of ivy over the entire south side of the home will shade and cool the home further from the summer sun.
- External Window Shading - Exterior shades above the south facing windows will block the summer sun from directly entering and heating the home.
- Low Wattage Lighting - Less heat from lighting indoors reduces cooling load.
- Ceiling Fans - Reduces the perceived temperature by three degrees (F) when running.
- Interior Thermal Shades - Increases the R-value of the window and can both help block heat from entering during the day or cool air from leaving during the night.
- Natural Ventilation - Natural ventilation from both the windows and the Ultra-Aire unit help to cool the home naturally day and night.
- High Thermal Mass - The exposed concrete slab floors on the ground floor (and possibly the bathroom) will absorb and store heat during the day and release it during the night if naturally ventilated. This is a cycle that can repeat each day.
Hey, that’s not a bad list. I have lived in a number of rowhomes and apartments in Philly now and many did not have any of these passive cooling features. We were still able to keep cool enough without A/C by simply opening the windows on both ends of the home. Many homes, we only had a window A/C unit in our bedroom to make it a bit more comfortable to sleep at night.
There are a couple of key features in this list to me. I think the first is the very basic ceiling fans. By lowering the perceived temperature by three degrees when blowing directly on occupants, we now can raise the thermostat to 81-83 degrees (F). With all of the other features helping us out, I don’t see how we couldn’t keep the home at that temperature simply by naturally cooling the house with outside air during the night when it is 17-19 degrees (F) cooler on average in Philadelphia. It could be 100 degrees during the day, but it will most likely drop to near 80 during some point in the night and this is a worst case scenario for Philly that would not last more than 1-2 days.
LEED & Budget Impact
So how will this effect our budget? With the model of dehumidifier we have chosen, we have the potential to eliminate both the HRV and the Ductless Split Air Conditioners from our budget. These two items are currently taking between $8K - $10K of our budget. I am assuming that installing the Ultra-Aire will be much cheaper than this figure and will free up some HVAC budget that we can shift towards a solar thermal system to handle all of our domestic hot water demands year round. I’ll take it if I can get it!
The last thing we need to verify is that we will not be violating any LEED prerequisite by not installing a traditional A/C unit to cover the calculated cooling load of the home. I would hope not and I don’t see anything at first glance, but we have MaGrann verifying this for sure now.
16 comments ↓
Those are some great tips, for sure. I’m sad the dehumidifier is for full-house systems. Have you come across any that I could add to a 125-year-old house in a retrofit? We have steam radiators, so forced air really isn’t an option.
Chad,
I live in Lancaster, PA and completly agree with your assesment of the required cooling in this area, dehumidification is the key! I definitly think the (mostly) passive cooling and dehumidification that you are providing will be more than sufficient.
I always think in terms of if I end up owning this thing forever, would I want “x”, in this case a/c. You also have to remember that the average home buyer is not going to go through the thought process you did they will see the pictures, think it is small but neat looking (you know what I mean) and it does not have blah, blah blah in this case a/c or a garage or “x” so you can not keep cutting things out of the project.Great design can only overcome so many objections. This is just my opinion and I sweat alot so take it witha grain of salt.
Thanks for the comments guys.
Mark - Check the site that the dehumidifier is linked to. They have some free-standing models (Santa Fe) that are not for whole house use that might help you.
Rob - Thanks for backing up the concept with local input!
Millhouse - Thanks for the opinion. Try to think of it not as a home without A/C but without traditional A/C. We are still conditioning the air by actively removing humidity just like any traditional A/C unit would do. Then we are simply cooling the air with a whole bunch of passive and mildly active methods. Also, the person buying these homes will be far from the average homebuyer which gives us a bit of leeway…
I’m assuming that with the humidifier being a whole house system you’ll be needing to do some traditional duct work as would be done with a traditional A/C system correct? If that’s the case than it shouldn’t be too difficult for a future owner to just buy an A/C unit and have it hooked up if they really wanted.
Assuming my above assumption is true, you might want to think about the design in order to make it fairly easy for a future owner to make this upgrade if they so choose. I personally think the passive cooling system should suffice just fine, but a lot of people do love their A/C.
With only 6″ and 10″ round inlets and outlets I’m not sure if we will be able to accommodate a future A/C system but it is a very good point and worth looking into.
I would consider putting A/C for free in the future if the client was unhappy with the system. This makes me a bit nervous though as it requires determining someone’s unhappiness levels…
As a former realtor and long-time Philly resident, I’d agree with millhouse: you’d really be making things more difficult for yourselves by foregoing traditional A/C.
Sometimes difficult is a nice change of pace from impossible.
Thanks for posting you house plans/progress. My comments (..please take what’s useful and toss the rest)…
1. those whole-house dehumids cost about $2200. A Sears Kenmore free standing one goes for about $230. Your place will be small enough one for the bedrooms at night might do it.
2. The kitchen counter-bar area makes sense but is the area behind it -the 10ft distance to the wall-the eating area? With a table in there, and the small passage between the fridge and counter, you may be constantly running over your housemate especially if in a hurry. Suggest you move kitchen counter to the wall and have a table on rollers for dining. Then put the fridge in the corner- where it is now everytime it opens it blocks the passage to the kitchen.
3. If you can turn the bathtub lengthwise against the wall you will gain a few feet of more useable floorspace. Otherwise the narrow area along the tub is just for getting in it. This will be especially good if a couple both want to brush teeth at the same time. It’s so romantic! you might even fit 2 sinks that way. woo woo!
4. the location of the stairs creates a narrowing of both the upper and lower floor. If possible, locate it along the shortest wall at the entrance to the house. that way a loveseat can go under it and a coffee table creating a reading nook. Or make it a bookcase, or put the tv under it on floor 1.
5. I am not sure how much passive heating you will get in the summer unless there is more sunspace/windows on the south side.
6. The tall narrow windows are nice, but suggest at least one “picture window” visible from couch area or eating area. If the local views are not nice, put it high enough to see treetops, clouds, or even birds on an electric line.
7. Make sure the diagonal views through each floor are as open as possible, preferably with windows extending the diagonal outside. Makes for nicer small rooms.
Thanks for letting me kibitz!!
DB
The dehumidifier does not appear to be for a ducted system, and I think the whole idea of this is to reduce (less ducts), not to allow the homeowner to increase. This is being marketed as a green house and if you are going to do it, do it right and make it a green house. Not a house that sucks a ton of electricty so that its residents can have it refrigerator cold during the summer. I have lived most of my life (about 23 of 28 years) in this same climate and I see no need for AC, I am however not normal.
People who are intersted in this house will want to live there for the green benifits and will have to understand that low cost green can be acheived but with mostly passive systems. This means that the inhabitants will need to participate and close blind or open windows as the day changes, its part of living a lowtech, green lifestyle. If they want it all done for them this is certianly not in the 100K budget to have completly active and hightech systems…Rant over.
Rob,
You are right on with your assessment! Feel free to rant here anytime.
dbomberg,
I’ll try to address your questions as best I can:
1. Room units may be a consideration for supplements to an HRV or ERV. They do not bring in fresh air as the whole house unit does though, cannot be hooked into a central control system (programmable thermostat), can be unsightly and have to be manually emptied if a convenient drain is not near the unit.
2. Noted. Ten feet in the city is actually a pretty large space to put a narrow, long table.
3. This was the original design. The new design is a bit more unique and adds a modern flair to the bathroom. Two sinks is out of the questions as it is excessive for our design…
4. This would require entering directly into a bedroom and passing through it to get to the bathroom and second bedroom. This orientation was considered and passed on early in the design process.
5. We are actually right in the range of window space needed on the south with about 11% of the floor area of the house. The problem is our house is not truly south facing and is more like south-west.
6. Picture windows are going on the south side where we can afford more window area. We are already slightly over the amount we were targeting on the north side.
7. Good suggestion. We will consider before finalizing the window placement.
Thanks for the comments and welcome to the blog.
- Chad
Have you considered an indoor air exhaust fan placed high near the roof line with inlet air provided by low windows near ground level ?
The only concern I have for a NON AC house in the city is noise abatement issue. AC is used to overcome street and neighbor noise (dogs, traffic, basketball bouncing, kids) all common to row house living. Your SIP panels and new construction should minimize this as compared to a normal row home.
Ben,
We are trying to design the windows on the second floor of the south side to be twice the area of the opening windows on the ground floor of the North side. When both sets of windows are opened this will create a natural current from the bottom north windows to the top south windows.
We are also looking into cooling techniques using the HRV/ERV that will still allow all of the windows to be closed during the summer if desired. This is especially important at night when people want more quiet to sleep. During the day it most city dwellers become accustomed to the “city noise” and actually grow to like it…
Questions:
Will the windows be left open when the house is unoccupied ?
Is security an issue in the neighborhood ?
Will windows if left open be shielded from rain ?
What is the operating style on the lower windows on the street side of the house ? Casement/awning inward or outward operating ?
Just thoughts from a lifetime Philly row house owner.
The windows will not need to be left open while unoccupied. The idea of the whole house ventilation system is that the exchange of fresh, cooler air can be done through a series of vents without ever needing to open the windows.
If the temperature and humidity levels are acceptable outside, then the homeowner could choose to manually override the system and open their windows for natural ventilation.
Leave a Comment