GSHP vs ASHP
Newbie here sorting through first build in ICF and awaiting Architects preliminary sketches. House is 1650 sq ft per level, 2 levels plus basement and a separate 400 sq ft garage with apartment above. As well as heating for this there is the driveway to heat approx 1500 sq ft and a swimming pool 900 sq ft. We’re on 2.5 acres in Napanee Ontario near Kingston with space for GSHP.
Really early days yet, house is barely a collection of ideas but what system would work for us, CC ASHP or GSHP. If it was 4 or 5 years ago I would have leaned on GSHP but there seems to be a lot of improvements in efficiencies with ASHP. It’s hard though to find a consultant who would objectively give us costings on the options. They seem to push one system or another.
Are there limits to how much an ASHP can cope with since we’re adding in driveway heating and pool? In which case we’re back looking at GSHP.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
You won't find many options for ASHP heating of a driveway. It also works best with lots of BTU over a short period (eg, 200,000/hr for a few hours) - that's expensive with any heat pump (unless you have thousands of gallons of water tank to spread the load over time).
Here is one:
Off topic, but ICF is neither "green" , nor the most cost effective way to construct a house. Concrete and foam are near top of the list in terms of carbon foot print and pollution.
Heating a pool and driveway(!!) isn't all that green either.
Jevon strikes again.
When you run the numbers, an occasionally heated small driveway isn't nearly as bad as one would think - especially if it's mostly used to remove the little bit remaining after plowing.
Generally the belief is that Air Source Heat Pumps are less efficient, but significantly cheaper to install relative to the ground loops (the indoor system can be largely the same), the cost savings of the extra efficiency doesn’t make up for the disparate install costs. Perhaps on a new site, if you already have to do tons of excavation, these costs are already largely accounted for in your build. Not sure.
In terms of the pool, I would find a way to design things where the excess heat removed from the home is used to heat the pool, and if possible any hot water for the house. Likely however, the heat load of the pool, will be significantly higher than the cooling load of the house. This is like a GSHP, but, using the pool as the water source. Perhaps your heating contractors can work this out.
The driveway heat system is another matter entirely. Consider that the pipes heating the driveway need a mixture of glycol (or other antifreeze) to prevent them from freezing, and this glycol both degrades the ability of the pipes to transfer heat, and also corrodes the pipes over time. There is some real maintenance to deal with on this particular item. What is the BTU load of this item?
For air source, you might be in the range of the smaller LG multi V S. With a low temp and high temp hydro kit, you can get your pool heated and hot water.
Provided you size your hot water tank right, you can use the heat in there for the occasional driveway de-ice.
One of the biggest issues is finding somebody to size, configure and install the system properly.
The smallest unit to support the hydro kit is their 5 ton Multi V S, so you have to check if your loads fall within the range.
Thanks everyone, since it’s a new build I figured there might be a few cost savings in GSHP having the excavator onsite doing foundations already. I’ll talk to a heating engineer about ASHP and what we might need.
I’ll split the driveway heating off and see if there’s a separate system for it that might make sense. I’m not heating the whole driveway, just a path and an area in front of the house that may be way smaller than my initial estimate. The rest I’ll use a snowblower on. The pool heating is just to lengthen the months it’s usable, maybe there’s a solution for this.
I think the Multi VS is only rated down to -4°F, not nearly enough for Ontario weather.
>"...only rated down to -4°F, not nearly enough for Ontario weather."
That should be "...only fully specified down to -4°F...". It will still run at temperatures much lower than that, and with a reasonable oversize factor (or a RIDICULOUS oversize factor, in the case of a 5 ton), it will do just fine in a Napanee/Kingston type climate. The only caveat would be that it doesn't come fitted with a pan heater for managing defrost ice build up, and would have to be monitored during extensive cold weather operations. That's not a big deal- may ASHP without pan heaters have been running for a decade or more in climates cooler than that. But if that's an issue for this homeowner, it's time to find another alternative.
I stand corrected then. Not very familiar with those units, should've taken a closer look at the specs. Thanks for the info!
It's not just LG- all air source heat pumps are only fully specified down to some temperature in the capacity charts, but all of them keep going at temperatures lower than what's in the extended temperature capacity charts.
Just because the heat output and efficiency at temps below the bottom of the chart aren't specified doesn't mean the output automagically drops to zero, it only means it's output and efficiency not specified by the manufacturer when operated out of the specified temperature range.
Most Mitsubishi units have an outdoor temperature sensor calibration/error condition that occurs at some temperature below -18F (which is 5F colder than the coldest temp in the chart) that the controls sense and turn off when it reaches that unstable range (presumably to self-protect) but returns automatically to normal operation somewhere between -18F and -13F. Vendors understand that sometimes the equipment will be operate outside of the fully specified temperature ranges- they just won't give you a number of what to expect.
It's sometimes a problem convincing the code officials that it can still heat the place even if the local outside design temp is a few degrees below the coolest temp in the chart, since they may need to see it in print from the manufacturer to believe it.
The 99% outside design temp in Kingston, ON is -7F. With any oversizing factor at all a unit specifed at "only" -4F would cover the 99% load. I'd be a bit reluctant to install it in Kenora though, where the outside design temp is -22F.
Aventino68 - is your new build by chance located on County Road 7 in Loyalist Township?
It sounds like your loads will be outside the range of using an ASHP, assuming cost is a factor. They make air-to-water heat pumps like this one: https://www.nordicghp.com/wp-content/uploads/2019/05/ATW-Brochure.pdf that might be able to produce enough btu's to meet your loads with a appropriately sized buffer tank. Once you nail down your building, pool, and driveway loads, you could find out for sure.
Not to be a shill but if you end up needing someone to size and design your HVAC system, the firm I work for in Havelock ON could help you.
Be careful with the GSHP, it's highly dependent on site specific design to make sure it works right. Make them show you a load calc and how they arrived at their piping layout/lengths. An eyeball is not an effective method.
Matt we looked for a year or so on County Road 7 but nothing turned up so we ended up in Napanee.
I’ll have a look at what we need btu wise when the architect gets back with more drawings. With the bulk of the driveway getting cleared with a snowblower we may be able to use electric for the remainder.
Landscape architect has put in space for some solar and therefore net metering so electric for the small portion of driveway might still be economic.
The 5 ton unit can be connected with heads down to 50% rated capacity, at which point at -25C it delivers 32kbtu. That is in a ballpark for a 3400sqft house. I can't find the minimum system output so hard to tell how well it will modulate.
There is also a pan heater kit for the larger unit.
Thanks for the responses, plans finally back from architect, two levels in total 6862 sq ft of which 1053 sq ft is garage. Need load calculation next. Heating pool separately using solar and own pump system since I'm doing 10KW back onto grid and have an area with solar on ground mounts, will put up a few more mounts and run pool heating through it. For driveway, will only heat 15 x 20ft in front of garage and path/steps leading to house (so I can get from car to house avoiding ice) and initial thoughts are electric seems best here.
So that leaves me looking for an ASHP system for the house based on the Kingston ON climate. Plans show a gas fireplace in Living room and a woodburner in 3 season room. Won't go for in floor radiant heating. But I might do electric floor heating in bathrooms. What is the consensus on ducted ASHP vs Mini splits for a new build that's quite open plan. Unless I'm confused I can only find Cold Climate ASHP ducted systems and I think minisplits would struggle with our open plan design ?
What are your cost of fuels? This would help me narrow down what is truly green and what has a lower cost of ownership.
Have you considered GEO? This would allow you to dump some heat from the home into the pool in the summer. And, this isnt effected by the cold weather up north.
The other thing to consider is an accurate heat loss and manual J calculation.
Often when I perform these after an engineer has done so, my numbers are lower due to real world considerations.
For a home around 5000sq ft of occupied dwelling, a ducted system would pay dividends. With having closed bedrooms and offices, and possibly a not so open floor plan, conventional mini split system will leave you with many interior heads, lots of piping, and poor dehumidification due to the poor turn down ratio.
Reach out if you need assistance.
For clarity , GSHP is Geo , so to speak . Ground source heat pump however is different than GeoThermal . GeoThermal in it's true form does not require mechanical operations to extract heat from water whereas GSHP relies on that operation .
>" Unless I'm confused I can only find Cold Climate ASHP ducted systems and I think minisplits would struggle with our open plan design ?"
You're probably confused then. Even on cozy 6700' weekend getaway places with 1000' garages such as this it's possible to spec (ductless or ducted) mini-split solutions. It's not likely to be a single compressor serving the whole shebang though. Kingston's +2F/-17C outside design temperature isn't particularly challenging.
When you have the room by room, zone by zone load numbers setting the " Heating Capacity (Max Btu/hr @5℉) " cursor 10% -40% range above your design temp load for those rooms or zones would allow you narrow down this database of air source heat pump products, most of which will be mini-splits:
Ok so next up I'll get the plan more detailed and work on room by room, zone by zone load numbers and that will give me what btu we need to run the system. Then from there I can look at Propane and power costs and figure out the best way forward. David