AN EXPERIENCED H.V.A.C. CONTRACTOR submitted today a proposal for a two-stage HVAC system for the Social Hall. The installed cost of a ventilation system would be $28,000. Later, we could add heating and A/C for another $21,600, plus the cost of electrical work. Subtotal: roughly $50K.
I asked for this bid because the Ad-Hoc Committee on Capital Priorities recently named such ventilation one of its top five items:
“The Social Hall should once again become an integral part of Mishkon’s life. [It] needs new ventilation and heating.”
Below the jump, I describe the elements of the vendor’s proposal and discuss them, including related options.…
VENTILATION STAGE
The ventilation proposal from Jessy Perets, owner of Grand Heating & Air Conditioning, includes the following items. (The first 4 are discussed below, in turn.)
- Two fan-coil units (with blower motor), one for each side of the room
- Supply ductwork and registers, for each side of the room (see photo above)
- Hospital grade filtration (MERV-13)
- Two duct smoke detectors*
- Two thermostats
- Return ducts
- Removal of old equipment as needed
- Installation of new equipment
- Electrical connections for the fan-coil units
The system would nominally provide 80% filtered indoor air and 20% fresh air, to be drawn through an enormous existing duct that vents from the wall at the top of the emergency exit staircase alongside the play yard (hidden under the shed roof).
FAN-COIL UNITS
The Carrier FJ5 fan coil model looks something like this (cutaway view):
It has a 5-speed ECM-type blower motor, which is relatively energy efficient and capable of handling a hospital-grade air filter (which restricts air flow compared to standard filters).
This fan coil appears to be a middle-of-the-road choice in the Carrier product line, in terms of its cost versus energy efficiency, noise reduction, and other bells and whistles.
These units would be installed in the mechanical room (sometimes called the “dungeon room” because of its heavy fire door) in the southeast corner of the Social Hall.
Carrier fan coils are covered by a 10-year parts limited warranty upon timely registration, at least in residential applications.
SUPPLY DUCTWORK
The supply ducts would be mounted along the top of the long walls. They would be spiral ducts (rigid, spirally wound tubes made of metal), with a register (grille) located about every 10 feet.
Advantages of spiral ducting (versus traditional rectangular ducts) include: more energy efficient, quieter, better airflow, stronger and more durable, and offering a clean, uniform appearance.
FILTRATION
The MERV-13 filter rating is considered to be at the low end of hospital-grade filters, offering some protection against airborne viral or bacterial infection. It seems optimal for the Social Hall, especially given we have some standalone filtration units already. Other things being equal, a higher MERV rating would only slightly improve the amount of purified air delivered, while increasing energy and filter costs.
VENTILATION ADEQUACY
The proposed system would provide 4 air changes per hour in the Social Hall.
Twin fan coils @ 1750 CFM each (blower rating) = 3500 CFM
3500 CFM ÷ 52,026 Cu ft/ air change * 60 min/1 hr = 4.0 ACH
Because that level of air turnover is considerably less than the 6.0 ACH that is generally considered the standard for avoiding the transmission of airborne diseases, it would be prudent to continue to operate the standalone filtration units in the room, to supplement the mechanical ventilation system’s filters.
DUCT SMOKE DETECTORS
A duct smoke detector is an HVAC-system device that can prevent flames and smoke from being fanned by the system. In the event of smoke, the detector sends a signal to shut down the fan. Jessy has included a pair of them in the belief that its presence is required by code. However, the applicable codes appear to exempt systems whose fan is rated at 2,000 cubic feet per minute (cfm) or less. And according to an email from the manufacturer (Carrier), the rating for the proposed fans is only 1,750 cfm. Therefore I believe that this system would be exempt from having smoke detectors in the ducts. And so I have not included the cost of those devices in this post.
HEATING AND COOLING STAGE
This ventilation system is compatible with twin heat pumps that could be installed later on the roof. The present installed cost for those heat pumps would be $21,600, not including the cost of an electrician’s wiring work.
The recommended Carrier 27SCA5 heat pump appears to be the bottom-of-the-line model for that manufacturer. Its energy efficiency (SEER2) rating is 16.0, which is better than the state-required minimum of 14.3, but lower than their other models. Yet because we are not likely to use heating or A/C much, this model is probably optimal for us, in terms of capital efficiency. (Energy-efficient units cost more.)
The proposal is for two 5-ton units. That is actually half of the capacity that would be called for according to standard engineering calculations. But because decades of experience have shown us that we seldom need heating or A/C in the Social Hall, this sizing seems optimal; it should take care of the vast majority of our HVAC needs. Again, it enables us to use our capital efficiently.
Just to be clear, some of the cost of the ventilation stage of the proposed system is for the coils, which are really needed only if the heat pumps are eventually installed. I.e., we would be paying up front in order to have that flexibility later.
Although the Ad-Hoc Committee did not make A/C a high priority, it turns out that the added cost for A/C is not much different from installing heating alone, which Jessy says would cost roughly $20K. That’s because many of the components are shared in common. Jessy also believes that if the room were filled with people, there would be a felt need for A/C due simply from the heat generated by so many bodies.
Like the fan coils, Carrier heat pumps are covered by a 10-year parts limited warranty upon timely registration, at least in residential applications.
(BTW, Jessy told me that it’s not worth paying extra for the Carrier model with extra corrosion protection “for a coastal environment.” He says it is twice the price and doesn’t last. Instead, he recommends monthly spraying a certain protective coating on the exterior of the heat pumps and of our existing rooftop condenser units; I think THIS product is what he was referring to.)
Rough cost comparisons
With Jessy’s proposal, we could get full HVAC for the Social Hall (including installation, but not the attendant electrical work) for roughly $50K. He says that it is $2,200 less than his standard pricing.
CaptiveAire’s quote in April for equipment only was more than $65K. (Installation would be extra.)
The Historic Structure Report (HSR) offered an estimated cost of $42K in 2003 dollars, which is equivalent to more than $71K in 2024 dollars.
I.e., there is indeed reason to think that Jessy is offering a relatively inexpensive approach.
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