CaseyFCC2215 | Posted in General Questions on
Any advice would be helpful thanks!
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My bet is the consensus here will be that the money would be far better spend on improving the envelope, and a mini split or 2 if AC is desired.
If natural gas is available, it is the least expensive way to heat
Yes I agree but my client unfortunately does not. No Natural gas either.
Is natural gas cheapest? Consensus here seems to be that mini-splits are cheapest.
My experience has been mini splits are definitely cheaper than both oil and gas. The monthly connection charges and fees here are like $25 a month or $300 a year before you even use any gas. I have net metered solar but If I had to purchase the power I would have spent less this winter so far than just the connection charges alone to run my 2 12k mini splits. I use a heat pump water heater for hot water which is way cheaper and efficient to run than gas as well.
>"Is natural gas cheapest? Consensus here seems to be that mini-splits are cheapest."
At MA type (nearly the highest in the nation) electric rate and (also pretty high) natural gas rates it's cheaper to heat with condensing natural gas, with margin.
Geothermal tends to run $9-10K/ton in MA too (more that that for 1-2 ton systems), which is ridiculously expensive. If on one of the larger and more expensive net-metered utilities in MA (Nat'l Grid, Eversource) it's usually more cost effective to go with air source heat pumps + rooftop PV.
No matter what the solution, the first and most critical thing to get right is the load calculations. Do NOT let the HVAC contractor (especially a geothermal contractor) run those numbers- hire a certified P.E. who regularly does Manual-J calculations as a service, and make sure they understand that due to the extreme expense of geothermal it needs to be done as aggressively as possible. Also solicit suggestions for cost-effective upgrades to the building envelope, with the load numbers of the "after upgrades" version of the house.
>" I like not having a buzzing compressor outside my window. I believe that its inherent sensibility means it will be efficient."
With the exception of Dandelion Energy (not currently operating in MA), every geothermal system is a custom-designed system, fraught with design error risk that can bring even the best water to water heat pump to it's knees for as-used seasonal efficiency. Vet your contractors VERY carefully. There is a lot of pumping energy needed to move that ground source loop, and high velocity air handlers can chew through a lot of power too. Even though a perfectly designed perfectly implemented low-temp hydronic geo system can hit a seasonal COP north of 4.5 (HSPF 15) for the whole system, all power included, in a retrofit that requires a substantial amount of low-temp radiation. A more realistic expectation would be an average COP of 3.5 (HSPF 11-ish), which is pretty easy to hit with air source heat pumps in a MA climate.
Air source heat pumps with scroll compressors don't buzz (though not totally silent, they're pretty quiet), and there is no reason to install them outside your window. Most noise issues with mini-split compressors is the low frequency vibe when the unit is mounted to the wall. There is no reason to mount it on a wall either, but you DO want to mount it high enough that the bottom pan is above the record high snowpack depth in your area.
The real performance difference between best-in-class air source heat pumps and geothermal isn't average efficiency, but rather the efficiency at peak load. When it's sub-zero outside the geo system will still be hitting it's COP 3.5-4.5, whereas a best in class air source heat pump will be running a COP of 2. But binned hourly mean outdoor temps in January in almost all MA locations are north of 20F (it might be cooler than that on the summit of Greylock in January) and in coastal locations they're north of 25F, and in the Cape & Islands north of 30F, and that's just the coldest month. Properly sized an air source heat pump really CAN hit a seasonal average a COP of 3.5, even if it's burning nearly twice the power of a better class ground source heat pump system when it's below 0F. But the total number of hours in a year that it's below 0F in any MA location is mini-scule, and doesn't much affect the average efficiency.
So I'm that guy. I want geothermal in my new house. I'm drawn to the idea that it works just as well on the hottest day and the coldest night as any other time. I like the idea that once my well is drilled it will last forever, just the compressor has to be replaced periodically. I like not having a buzzing compressor outside my window. I believe that its inherent sensibility means it will be efficient.
While I'm generally in favor of efficiency improvements, I'd argue that if you're not going to make those improvements, then the more inefficient the house the more sense a high-efficiency heating source makes.
I'm a numbers guy. To talk me out of it you'd have to show me calculations that this thing isn't going to save much energy in reality.
I'd add that you have a business opportunity to sell some efficiency improvements to the house. If I'm installing a whole new HVAC system, and tightening the envelope allows for a smaller system that costs less, the payback period for those improvements is right now. With geo the biggest cost is the wells, and you need a certain amount of well per ton. There's a very direct proportion between system size and cost. So if the installer says, "with the house the way it is you need a 3-ton system which costs $30,000, but if you insulate the attic you'd need a 2-ton system which costs $20,000, and insulating the attic costs $5,000," that's a pretty compelling case for insulating.
>"There's a very direct proportion between system size and cost. So if the installer says, "with the house the way it is you need a 3-ton system which costs $30,000, but if you insulate the attic you'd need a 2-ton system which costs $20,000,"
That never happens.
A 3 ton system only rarely comes in at $30K, and a 2 ton system literally never comes in at only $20K. If those are the kinds of numbers they are using it's time to get VERY skeptical about the competence. There is a base cost they need to recover for designing the system that doesn't change with the bill of materials or the depth of the wells, and it's not cheap. Most contractors will still want to oversize the system even when handed a third party Manual-J performed by a competent engineer.
GSHP installers are not in the building-improvement business. While some will point out the lowest of the low hanging fruit, building performance isn't in their wheelhouse.
>"I'm a numbers guy. To talk me out of it you'd have to show me calculations that this thing isn't going to save much energy in reality."
In this MN study involving in-situ monitoring of dozens of GSHP installations, the heating seasonal performance median was a COP of 3.19 (~HSPF 11) and the 75th percentile was a seasonal COP of 3.75 (HSPF 12.8). The 25th percentile was a none too impressive COP 2.88 (HSPF 9.8) See Table 7, p33 (p44 in PDF pagination):
So about half of the installations did no better than a typical ducted Fujitsu or Mitsubishi, and many did worse.
There are other older studies with a smaller cohort of systems under study, but the trend is similar, no matter where it is in the country. Unless you're designing in VERY low temp radiation you're very unlikely to beat a seasonal COP of 4, even with an ultra-competent system designer. It's pretty easy to hit an COP of 3.5 with air source heat pumps in a MA climate with a competent designer and careful sizing.
Just to be Contrarian, is it fair to compare the average installed performance of ground-source with the specified performance of air-source? Air-source installers mess up too.
I have a cottage up north which is around Zone 6 climate where I recently had a deep well drilled.
I can definitely say that there is no way to justify the cost of even getting one more drilled, never mind the two needed to get near the capacity to heat the place with a GSHP.
Compared to even the cost of a brand name cold climate heat pump, the extra bit of efficiency improvement, the ROI on just drilling the wells alone, never mind the equipment is many many decades.
Horizontal fields are cheaper but lower COP, so you are still spending a fair bit for a marginal efficiency gain.
>"Just to be Contrarian, is it fair to compare the average installed performance of ground-source with the specified performance of air-source? Air-source installers mess up too."
Yes, it's totally fair.
Air source heat pump systems are "HVAC systems in a can", with very few things needed to get right. Air behaves pretty the same everywhere- local humidity & temperature determine the local average efficiency. The only way a system designer can screw it up is really the sizing, or by using completely inappropriate equipment designed for more temperate climates.
Of course the more idiot-proof you make something, the more creative the idiots become, but a reasonably self-educated homeowner lurking on this site can probably spot the inspired creative geniuses of the air source heat pump world and avoid them.
By contrast there are myriad ways to screw up geothermal, at both the system design and implementation phases. Every system is a custom system, with lots of ducks to get in a row to achieve the theoretical efficiency numbers.
Electricity in mass is high, so Gas would be cheaper
I think 30k might dig you the wells.
Get realistic quotes for you client, double check them with actual installs, don't let a contractor underbid and then add on. Get references, with prices.
Geo is blindingly expensive to install, and you need a lot of space to do it
Get an air source heat pump number
Let the numbers do the talking
“My client currently has oil forced hot water.”
Is the current system forced air with domestic hot water or is it an oil boiler feeding hydronic heating loop?
For forced air In terms of dollars recouping the well drilling costs in electric saving compared hyper heat mini split is very unlikely.
For geothermal the pump usage is a total wild card. The horse power is random choice of the installer. The loops and wells are all different from one sire to the next.