I’m planning to construct a home sometime in the near future in hot, arid part of the country. Obviously, keeping the home cool is a major concern and I’ve been considering all available options.
One of the recurrent ideas discussed online is using geothermal cooling. But I think I don’t have enough land to implement it. I have a related idea though.
Water supplied during set hours of the day by the municipality is fairly cool even during the summer months and it is a common practice around here to first let it collect in an underground tank and then pump it to the overhead tank as needed.
What if I create a closed loop system of circulating water with two car radiators: one in the underground tank, submerged in cool water and another in the living area of the home with a fan blowing behind it.
Do you think it’ll cause perceptible change in room temperature if there is, say, a temperature difference of 10 degrees Celsius between water and ambiance? I intend it to only reduce the load on the air conditioners and/or just delay the use of AC.
What kind of math/physics will be needed to assess if this is a feasibility? I tried looking hard but could not find anyone else discussing this idea, so I’m reaching out to you guys.
Thank you for your time.
You’re describing a fancoil supplied with cool, regularly replaced, municipal water (normally this water would be a fully closed loop cooled with an air source or ground source heat pump). Your energy needs will just be a circulation pump. You’ll probably notice a little cooling but it depends on how cold the water is, the surface area of the radiator, and the flow rate of the water. It has the advantage of being low maintenance so give it a shot and perhaps build it in a way you can access the components and improve / experiment over time.
Look into an approach / methodology called Passive House. Passive House focuses on making buildings that have near zero heating and cooling load. If you get the math right / design from scratch with this in mind you can make a Passive House in nearly any climate. Common modern single-family-home building techniques are generally not at all closely aligned with building a Passive House.
When trying to keep a house cool, here are the things I would focus on (in order of priority):
Reduce solar heating impacts: either place shade trees or awnings to block direct sun on the entire structure (or the windows at a minimum).
Build a highly-insulating enclosure (~R30 walls and ~R50 roof at a minimum, but you could push that further). If you are set on building with lumber you still can, you could building an offset double-stud wall filled with insulation, and of course an appropriate amount of exterior insulation a well. The goal in addition to insulation quantity is to reduce thermal bridging. Consider a “simple” house layout. Avoid too many corners / details / flourishes that add construction complexity.
Utilize free-cooling first: as your first stage of cooling, open large windows close to the ground and open clearstory windows in the roof / top of a stairwell or similar, it really depends on the layout of the home (and ideally the layout is design around this concept). This allows the heat to be drawn out naturally via convection. Include ceiling fans for comfort. This approach will work until outdoor air temperatures get quite high. Once free-cooling will not longer work
Once free-cooling will not longer be effective you can transition to mechanical cooling. Close all windows and cool your space either a high-efficiency air-source heat pump (and / or your free-cooling municipal water fan coil).
Similar to the design methodology to encourage natural air / heat flow out clearstory windows or “solar chimneys”, also consider just having higher ceilings where heat can pool but you won’t feel it. Your exhaust should pull from these areas.
Dedicated outdoor air system (DOAS): don’t design your mechanical ventilation system to cool using air (aside from the free-cooling described earlier). It’s inefficient. Hydronic heating and cooling (moving heat with water) is much more efficient. That means heat pumps for heating as well as cooling. Mechanical ventilation rates should be the bare minimum, just enough for fresh air but not for temperature control. Perhaps look at flow rates included in ASHRAE 62.1 or a standard more focused on residential homes. Also, your supply air can be separately ducted to each room (not a shared trunk), each being much smaller than what you see in a “normal” house, this gives more control for every single room.
ERV: of course you’ll want to install an energy recovery ventilator to capture what heat / “cold” you’ve worked to produce before instead of throwing it away along with your exhaust air.
For heating your domestic water, get a heat pump hot water heater (with tank). Instead of making heat it takes heat from the surrounding room and puts it into your domestic water tank. That means it “outputs cold” into the surrounding room, the opposite of a gas or electric resistance water heater.
Earth tubes: to naturally pre-condition your supply air by running it through the ground first. Another form of free-cooling but useful when the house is “buttoned up” because outdoor air temperatures are too high. This is when you’re only supplying minimum ventilation air.
Limit the things in the house that make heat. Efficient refrigerators / freezers (see energy star website), computers that are no more powerful than what you need, etc. Place these things in areas where the heat won’t bug you as much.
Hope this helps.
Holy hell, how do you know all this?
I can’t thank you enough for taking the time to write all of this. I have come across most of these concepts and have been considering them with respect to the options I have.
I’m trying to design the house considering the natural air flow and sun angles. There is a garden with trees on one side of my plot and I intend to make use of it while also planning for other sides. Currently I’m making house plans on my own and discussing with some people I know. This is helping me understand what we want/need, or not, in our home. At some point I’ll definitely take it up to the professionals. There used to be a community of floorplaners and home builders on Reddit but it was not much active.
Stone is the cheapest construction material in my area but it practically converts the house into a furnace unless the walls are very wide. I plan to avoid it at all costs. On my radar is a technology called EPS (Extended PolyStyrene) Core panels which are nothing but high density PolyStyrene with a galvanized steel mesh in it. It is supposed to be load bearing and good enough to build the roofs along with walls. It has been used in some countries at various levels of success though not in this exact form (with wire mesh). It is supposed to be highly non conductive in terms of heat and so good for maintaining inside temperatures with minimal cooling. Most of the material available online are either research papers or companies selling it, both of which only have the incentive to talk good things about it. I intend to go and meet people who have actually built using this technique and take their feedback before I commit to it.
As regards this pet idea of mine, I think the consensus in this discussion is that it will not cause much difference. But since it does not involve much effort/investment, I’m going to try it anyway.
Another cooling technology that has my attention is desiccant based cooling. That too has some research papers and a nice set of videos by Tech Ingredients (https://www.youtube.com/watch?v=5zW9_ztTiw8). It looks more daunting and more suited for humid regions/months.
I keep dreaming about a setup with evaporative coolers for dry spells and desiccant based thing for humid ones, assisted with this pet tech of mine.
I hope I’ll have the courage to implement these ideas finally.
Thanks again.