Recommendation for minisplits vs. gas-fired HVAC for new Massachusetts building
wdperkins
| Posted in Mechanicals on
I am building an energy efficient 15 unit apartment building in MA this spring. We can either go natural gas or electric. I am considering going all electric since the MA Energy Code is so stringent and the heat load will be relatively small even though there are very cold temps at times. We might even put on solar panels for the house meter.
The electric units would take up much less space and I would rather not have to put in gas at all. I am not thrilled about electric hot water heaters but understand that the newer tankless units are much better.
Any input would be appreciated.
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Replies
Bill,
Questions to consider:
1. Who would pay for the natural gas: the owner or the tenants?
2. Who would pay for the electricity: the owner or the tenants?
3. Whoever is paying for the electricity has to be ready to assume that ductless minisplits will be used for cooling in the summer.
I appreciate the quick response. All utilities would be by the tenant.
Bill,
It's hard to find gas-fired heating systems that are small enough to handle the load of a single apartment, so if you want tenants to pay for their fuel bills, an electric approach makes more sense.
Okay thanks. Have you had experience with any mini-splits?
Bill,
I have no personal experience. But if you enter "ductless minisplit" into the GBA search box, you will get links to dozens of articles that will provide you with hours of reading.
Thanks Martin
Tankless electric hot water heaters in a 15 unit building would require a substantial service upgrade, and may STILL not provide sufficiently good mid-winter performance when the incoming water temps are bumping on 35F or cooler.
Tank heaters are cheap, and have only about 20% of the instantaneous draw from the grid of a tankless. Sized for the biggest tub you have to fill the flow rates can be quite high relative to any electric tankless.
Heat pump water heaters would work at higher efficiency and provide some summertime dehumidification/cooling, but the noise factor is less than ideal for apartments, unless they can be at least somewhat sound-isolated from the living spaces. That's hard to do, since they have to be installed inside of conditioned space, and have access to large volumes of the conditioned space air.
For most of eastern MA the 99% outside design temps are high enough that you can use dedicated mini-ducted systems like the Mitsubishi SEZ-KD/SUZ-KA series, splitting the output between 2-4 adjoining rooms with very short duct runs. These things have have a rated output at +5F, and can operate down to -4F without much problem. For apartment units with 99% design heat loads of 7,000-14,000 BTU/hr @ outside design temps of +5F or higher this series is pretty dialed-in. See the heating capacity tables on p26: http://usa.mylinkdrive.com/uploads/documents/4297/document/17_8_SEZ_Ducted_Heat_Pump_Systems.pdf
For higher efficiency and/or colder outdoor design temps ductless wall-coil type mini-splits are better, but you may need to use resistance heating in doored-off rooms remote from the ductless head to be able to hit the code-required 68F at the 99% outside design temp with the doors closed, unless the heat loads of those rooms are VERY low. You typically need modestly sized triple-pane window and high-R walls floor & ceiling in the doored-off rooms to get there completely without resistance heat backup. Boston's 99% design temp is +12F, Gloucester & Worcester is +5F, but Springfield & Lawrence have a 99% design temp of 0F, which means without a specified output below +5F you can't guarantee it's enough heat pump. The Fujitsu RLS2 series is specified down to -4F, the Mitsubishi FH series and Fujitsu RLS2-H series are specified down to -13F & -15F respectively.
A deep energy retrofit on a 3-family in Worcester I consulted on a few years ago is heated with one Mitsubishi FE series mini-split per unit, and they have been cruising through these -7F / -8F nights just fine without resistance heating backup. They are ~30-50% oversized for their calculated heat loads at +5F so it comes as no surprise that they still cut it at lower temps, and given how this year has gone oversizing by about that much is probably wise. Oversizing by more than that results in on/off cycling rather than modulating for much of the season, with bigger room temperature swings, lower comfort.
Thanks Dana there is a lot to think about and your input is very helpful. I know that Mitsubishi also just came out with Hyper Heat units which are effective at even lower temps.
Having rentals remember to KISS problems and don't add to them. Renters have a knack for throwing curve balls. Simpler the solution, the simpler the fix. Go electric, never gas. Mini Splits I would avoid for renters just like you avoid wood stoves. Both solutions are best for heating, except for renters.
1.). Mini splits cost more which lowers your ROI. PTHP and similar solutions have a much lower initial cost.
2.). As pointed out on earlier post is that mini splits need outside condensers cleaned during blizzards. Tenants will not do this, so that means maintenance cost for you.
3.) Lower cost of KISS HVAC solution means better features on the rentals which means more ROI.
4.) Tight envelope with expensive mini splits require a expensive Air Exchange equipment lowering ROI further
5.). When HVAC fails how quickly and how much is replacement? I use PTHP's that I can swap out. Haven't had to yet. The fix takes 15 minutes if I do with little maintenance cost. Tenant is happy instantly and I don't have a problem I have to monitor all day.
6.). Go with normal electric water heaters per unit. Tankless uses too many amps and doesn't offer much savings.
I would say save money on HVAC, build a tighter envelope and add features to the rentals. Most savings is behavior base in efficiency savings. Also the main way to save energy in buildings is lower square footage. Since most rentals are smaller they have better energy efficiency per person with everything else equal.
How many PTHP's are available with a 0 degree F operating temp as would be useful in Mass?
How many with SEERs over 11?
Mini splits are cheap reliable and easily replaced. You can hang the condensers on the wall
edit.
does not seem there are any around that perform under 24F, so they would be running on electric backup for example, this year, the month of February.................
There are plenty of PTHPs that will run at 0F, but the compressor kicked off and the resistance heat went on when the outdoor temps dropped below 25F.
In all but coastal regions of MA the binned hourly temp in a typical January is 25F or lower, which means only about half the time would you be getting the ~2.0-2.5 COP of the PTHP, the rest of the time you'd be running a COP of about 1, with a seasonal average less than 2. (This February is turning out to be even colder than January in all MA locations.)
But if the tenant is paying the bill, who cares? Wintertime residential retail power rates in MA are "only" about 25 cents/kwh this year- they can afford it, right? ;-)
For cheap apartments the tenant may be just fine with the noise and low efficiency of a PTHP. Higher-end tenants will usually prefer quieter equipment and steadier room temps than what they would experience at the Holiday Inn Express, no matter what the efficiency numbers are.
On the other hand, though I am no fan of natural gas, current prices are very favorable, and if the infrastructure is nearby, then RINNAI direct-vent wall furnaces could be a very attractive heating option. These are very efficient (AFUE of 80-83) and reliable, and are available in capacities of a minimum of 3000 BTU up to maximums of 38,400 BTU. Worth considering.
@Dana- the Fujitsu ducted mini splits are a much better product than the comparable Mitsubishi units at this point...more or less same price, but better efficiency, much higher capacity at low outdoor temps and higher static pressure rating....and they can be installed in vertical orientation. The duct runs for either of these don't necessarily have to be short....they just need to be relatively smooth. I routinely use them for whole house solutions with standard length duct runs, but the ducts I spec are slightly larger and the fittings are smoother in order to keep duct friction down.
@Bill Perkins- There might some opportunities for higher efficiency central or semi-central hot water equipment if you're allowed and willing to meter and bill the tenants yourself using a flow meter or BTU meter. From an investor standpoint, a lot of these decisions have a lot to do with your particular market, likely tenant base and marketing. In most urban areas, there are "niche" clients who are VERY interested in energy efficiency and low utility bills and niche building owners who set themselves apart from the crowd.
Thanks for all of the detailed, thoughtful comments. The biggest downside for me in not using gas is the hot water, as I think we are leaning on going with some type of mini splits for hvac. I want to build a portfolio of these buildings, and take advantage of some of the great technology and construction methods out there to make them low maintenance, efficient and sustainable.
Bill,
Also, be sure to check out the incentives that are available through the Mass Save program...up to $4,000/unit for low-rise multi-family buildings....up to $60,000 in your case.
http://www.masssave.com/residential/offers/12-homes-rebates
On top of that (!) that are other rebates that you can add on to the above..."In addition to per unit incentives offered through the Program, participants are eligible for additional rebates for the installation of high efficiency heating and water heating, a supplement to assist with the cost of working with a HERS rater, as well as an additional incentive if your project is certified as ENERGY STAR®"
Think of all the money you'll save repairing all those broken pipes in the walls when the power goes out . Gas service does not often get interrupted and a smaller back up generator can be quite large enough to run some ECM circs and basic service stuff during times of need .
A little company in East Freeport named HTP right there in Mass has some real interesting stuff . The closer the greener .
Believe it or not, Massachusetts is still in a first-world country where power outages during cold weather long enough to result in pipes freezing is relatively rare... The last one in MA was the ice storm of December 2010- when I was out of power for 10 days, most people were out for fewer than 5.
And, in a better-than code apartment building the odds of any pipes freezing even IF the power were to be down for days during a cold snap go way down anyway. My (way sub-code antique house) pipes didn't freeze, and it got down to ~+10F for three nights in a row during that outage. Others in my county weren't that lucky, but again, that was primarily in housing stock way below current code for building envelope efficiency.
The notion that 15 HTP based hydronic heating systems are all going to keep chugging away when the grid is down is somewhat fanciful too. A 15 unit apartment building is going to need more than just a 5kw Honda to stay ahead of the hydronic heating & other loads even if they DIDN'T all have separate electric services. That might be a reasonable approach for single family homes though. District heating and islanded micro-grid power based on a ~10wk of co-generator might get you there, but that's a very different design problem (and cost-basis). You would have the ongoing operational cost of basically running you're own micro-utility- probably not worth it at the 15-unit building scale.