Multifamily HVAC Solutions
I’m developer of small (6-20 unit), low embodied carbon, low operating carbon, 100% electric multifamily housing in Minnesota and would love the community’s thoughts on the most efficient, scalable and readily available solution for energy efficient heating and cooling an air tight (<1 ACH50) building in climate zone 6.
The default for most multifamily builders here is either a PTAC in each unit, sometimes VTAC. In comparison to mini splits, these appear to use WAAAAY more energy and create WAAAY more opportunity for air sealing issues.
In the 6-unit building I am currently building (all 1-bed, 620 sf units), I opted to equip each unit with a its own 1-ton Fujitsu mini split.
https://www.fujitsugeneral.com/us/products/split/wall/12lzas.html
This works for 6-units…but isn’t really scalable.
So my questions:
(1) Anyone have experience with or thoughts Ephoca’s products?
Their HPAC and VHP products look like they address a lot of my needs. For example, the HPAC (specs attached) truly minimizes wall penetrations / risk for air leaking, look better than most PTACs, claims to be quiet, and is somewhat efficient (e.g. SEER of 16).
BUT…they don’t distribute in Minnesota yet, and I’m not Dana Dorsett so I can’t decipher how they would perform compared to my Fujitsu units in cold temps. Specific questions here are:
A) How do you get a distributor to pick up a product line?
B) How much importance should I place on having a local distributor carry it vs. buying direct from a distant manufacturer (service, maintenance)?
C) Would these be able to provide primary heat at -13F like the Fujitsu?
D) Directionally…How would the energy usage for one of these in a 620 sf unit compare to the Fujitsu I’m putting in? Not specific numbers…but order of magnitude.
2) What is the most energy efficient (and air tight) solution for a building comprised of 12-16, 625sf units…assuming a single zone heat pump for each unit is out of the question. VRF? HPAC + electric resistance backup?
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Replies
While I wait for someone like Bill Zephyr with more expertise to chime in, I'll offer that you might want to look at hydronic systems. Specifically, something with hydronic fan units that handle both heating and cooling. This is the traditional way that large buildings are heated and cooled. They are conceptually similar to minisplit heads but they scale much better.
Traditionally these are done with an air-source chiller and a fossil-fuel burning boiler. The question I would ask is whether there are emerging alternatives, including air-source heat pumps of sufficient size to replace the boiler, or even ground-source for the whole system.
It's also pretty easy to configure a hydronic system to use air-source heat pumps in mild weather and switch over to fossil fuels at a certain temperature.
Do you really want a central system with the heat and AC included in the rent pricing? This seems to bucking a 70 year old marketing trend. The other drawback to a central system is a single fault could easily take down the system leaving everyone without heat.
A Generally it is about volume how many unit a month will they sell.
B Generally the distributor do not provide service or maintenance with the exception of stocking some parts and sometime making them available 24-7 for an extra charge. Most manufactures will only sell to distributors.
C Not as a heat pump looking at their chart at 5°the unit is down 90% on heat output. They do list models with electric resistant backup heat.
D it seems unlikely you can do better than a mini split.
The reason PTAC are popular is that the system are so redundant no single failure can affect more than one room. When there is a failure almost no skills are required to swap out the unit for a spare unit. Also very low cost to install.
Walta
This is a good read about this topic:
https://www.greenbuildingadvisor.com/article/designing-multifamily-building-approaches-passive-house-performance
My takeaway is that building an energy efficient structure and heating it with resistance heaters is less costly than any heat pump solution. It doesn't take much extra effort to get near passive house performance at which point heating costs are small enough that there is no ROI for a heat pumps.
I remember reading about a multi family project that used a shared oversized HRV feeding a ducted air handler for a number of units. This way the shared unit was not only providing fresh air to every unit (which is needed if you make the place sealed) but also sufficient airflow to handle cooling loads. You don't need all that much cooling for a 600sqft apartment with well designed glazing and shading. Something like a 1500CFM HRV+5 ton air handler is probably in the ballpark for 16 units.
This would mean the owner still takes needs to cover some operating cost but in colder climates with an efficient AC unit, this cost is minimal. Tenets would still carry the larger cost of heating the place rest of the year.
Why is using mini splits out of the question? I have worked on quite a few multifamily buildings larger than that with similar systems. Sometimes finding room for condensers is an issue.
Multisplits could work here. I don't really see a problem with minisplits either, but you end up with a lot of outdoor units that need to go somewhere. It's not a pretty sight to have them all wall mounted on the exterior of a residential structure, so you have to either designate some part of the grounds near the structure for them (which seems most common), or have some kind of penthouse area for mechanicals (more common in the commercial world). One potential issue with multisplits is that while it's easy for the indoor units to be metered per tenant, the outdoor unit would be shared between multiple units and would need to be a common area operating expense for the building. Maintenance would be another issue, and keep in mind that certain types of problems in one unit (damage to refrigerant lines, for example) would take multiple units offline simultaneously, affecting multiple tenants.
To address DC's post that I must have missed back in April last year, the biggest downside with hydronic cooling systems is that they tend to not be very good at dehumidification -- the chilled water is usually running around 45F or so, and while that does allow for dehumidification in most cases, it's not as good at it as the much colder temperatures a DX evaporator coil can reach. The usual way to address this with a reheat coil, which is often electric (but sometimes sourced from building heat if steam or hot water is available). This isn't very efficient though, so you want to avoid running that way as much as possible.
I don't see a problem with a hydronic system -- that is how commercial buildings are typically setup -- but you have two big issues with that type of system in a multiunit residence:
1- small air handlers aren't particularly common, so you're somewhat limited on equipment for the cooling side. For heating, you could just use regular radiators, but those aren't a good option for cooling season.
2- with a large, central hydronic system, your entire building is either in heating or cooling mode. That can be a problem if you have one unit that wants 68F and another that wants 74F around the shoulder seasons, since you might have one unit that wants heat while another wants cooling, and you can't do both at the same time.
Note that the common walls between units don't have anywhere near the heat loss you get with an exterior wall, so your per-unit heating/cooling load numbers will be much less than you might expect for "middle" units (those with only one or two exterior walls), but will be more for the "end" units (those with two or three exterior walls).
Bill
In multifamily each unit typically has a separate outdoor unit on the roof or in a garage if it's open air. I've done this on projects with up to around 100 units, in podium type buildings so the distance to the roof is typically within what is feasible for the lineset. Every unit has full control (and the metering is all per unit vs a combined system). You usually want to gang the condensers on pads on the roof and then run the linesets into a pony wall.