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Thread: High velocity questions
03-15-2005, 02:15 AM #14Professional Member
- Join Date
- Apr 2003
- the Great Pacific Northwest
True hepa wont work just as a replacement for a standard filtration unless properly designed, either a bank of hepas with a pressure drop that meets unico specs or a fan powered sidestream unit. also hepa should have pre-filtration to extend the life of the hepas that load fast and are costly.
Out of curiosity why hepa in a residential application?
03-15-2005, 11:49 AM #15Regular Guest
- Join Date
- Mar 2005
Hvac tech lane, from what I've keep hearing from contractors on the job is that the architect and engineers have design alot of the systems similiar to what would be used in a commercial appliccation rather than residential. The home is somewhat large, I'm not sure if that's the reason. For instance he has scheduled redundant plans for multiple circulators in each zone for the radiant heat incase of fails. The hvac contractors want to reduce the number of coiling unit to four rather than six and want touse dampers to zone it to six zones of cooling. Changing the first floor to conventional and keeping the second floor and loft as High velocity. The propose using natures choice electronic air filtration and Aprilaire light commercial steam humidification. Any thoughts Thanks
03-16-2005, 11:45 PM #16Professional Member
- Join Date
- Apr 2003
- the Great Pacific Northwest
From unico web site tech note #109
Where the Unico System is located in conditioned spaces
and where there is no danger of freezing of water lines
there are additional choices. These are listed in the following
paragraphs from highest to lowest recommended.
1.) Heated Pan or Steam Type Humidifiers. One of
the more viable choices is the heated pan or steam
type humidifier that can be mounted in the supply or
return plenum. See Fig. 1 for detail of placement. In
such cases the plenum should be insulated sheet
metal. Because of the small plenum size and high
pressure of the Unico System, the return location
would be a better choice. A plenum box can be fabricated
to match the end of the Unico System coil module
and the humidifier mounted through the side or
on the bottom of this box that should be insulated.
When mounting through the side, keep the humidifier
as low as possible so obstruction of the airflow is
minimized and permit the air to flow across the top of
the humidifier-evaporating pan.
To minimize mineral build-up be sure to use a humidifier
that has a flush timer that replaces the water
in the pan periodically. If not built in, it should be
available as an optional accessory (e.g. Skuttle). Be
sure to follow the manufacturer’s instructions for periodic
cleaning to remove any mineral build-up. See
Table 2 for model listings.
I've not heard of natures choice filters and couldn't find them with a google search. A recent job I did was for a customer with severe allergies I used a large 2" pleated filter followed by a 1" cimatec 1500 electronic panel filter then a feild UV bio light, the customer has reported that her symtoms have been virtually eliminated with this system.
Multiple pumps for the radient sound like overkill unless the application is critical and going down would cause potential harm.
Six systems also sounds like a lot, did the engeneer do a heat loss/gain for the house? If the load diversity calls for that many systems then that's OK but many houses have enough diversity that zoning can do a fine job while delivering excellent performance and simplifying system design.
Unico company says zoning is OK if done according to their specs.
This Tech Note provides instructions for zoning the Unico
System for heating or cooling. Do not attempt to zone a
system without reading these instructions as there are
some limitations for doing so.
A zoned system is designed to independently heat or cool
more than one space with one or more units. Zone control
is accomplished by modulating the airflow or air temperature
flowing into each conditioned space. The best
method is dependent on the type of system and level of
Quite often in multiple story homes and buildings it is
difficult to design a system that will evenly heat and cool
each floor. It is normal that the upper floors require less
heat in the winter but proportionally more cooling in the
summer. Therefore, multiple story buildings are always
prime candidates for zoning.
Zoning with Multiple Units
The easiest and best method for zone control is to provide
separate units with their own thermostats. This keeps the
design simple and provides redundancy. A good example
is a two-story house where there are two units. Each unit
conditions each floor. This works well as the sleeping
area is usually on the upper floor while the living area is
There are no limitations for this type of zone control, provided
each system has the proper number of outlets for
the air flow required for that zone.
Zoning with a Single Unit
The type of system installed determines how easily the
system can be zoned. The easiest to zone is a hydronic
system – either chilled water or hot water. The most limited
is any refrigerant system – cooling or heat pump.
Systems with an electric duct heater fall in-between.
The simplest zoned system uses a separate plenum for
each zone. Each plenum should have a two-position
(open/close) damper with an end switch. A simple thermostat,
located in each zone, will open the damper and
close the end switch to start the blower. Additional relays
may be required to operate the condenser or boiler/pump.
Closing the damper (off cycle) will reduce the total airflow
and build up static pressure in the remaining open
duct. This could create noise in the remaining open ducts
by blowing more air than designed but the increased noise
level is not normally objectionable.
Refrigerant Systems All refrigerant systems automatically
balance themselves to the outdoor and indoor conditions.
Reducing the airflow decreases the evaporator
temperature and may cause the anti-frost switch to short
cycle the condensing unit. If the system is a heat pump,
reduced airflow could cause a high-pressure limit nuisance
Therefore, do not reduce the airflow below 200 cfm per
nominal ton. Likewise, do not bypass the supply air into
the return duct, as this is similar to reducing the airflow.
If you close off a main trunk you must open another. In
other words, make sure that the number of open outlets
remains essentially constant.
The most common type of system has two zones, where at
any given time, the airflow never falls below the minimum.
Delivering more than the minimum amount of air
is rarely a problem. To illustrate, consider the following
Example 1. Consider a nominal 3-ton application with
two equal zones. Each zone has a plenum serving each
area. The minimum airflow is 600 cfm so the system
requires at least 15 full open outlets. Both zones are installed
with 10 outlets. Each plenum has a two-position
damper that is fully open or partially open (in the closed
position). When either zone requires air, the damper in
the plenum for that area is fully open. Otherwise, it is
partially closed equal to half the airflow (or the equivalent
of 5 full outlets). With either zone calling for conditioning
the minimum number of outlets is 15 and with both
zones open the number of outlets is 20. Notice the number
of outlets never drops below 15 when the system is
operating. The actual number of outlets in each zone does
not have to be equal so long as the equivalent of the
minimum number of outlets is always open.
Example 2. Consider a nominal 5-ton system with three
equal zones with a plenum serving each zone. Only two
of the zones need to be controlled by a thermostat, the
third zone is common space (between the zones) where
the temperature does not need to be closely controlled.
The minimum airflow is 1000 cfm with 25 full outlets.
Both controlled zones have 13 outlets and the common
zone has 12. Use two-position dampers in each plenum.
The dampers are set for fully open or fully closed. With
either controlled zone calling for conditioned air, the
common zone is open and the minimum number of outlets
is 25. If both controlled zones require conditioned air, the
common zone damper is closed and the number of outlets
You will notice that the refrigerant systems in the examples
just shift the air from zone to zone. The system
never reduces the air below the minimum. This is called
load switching and it does not rely on airflow modulation.
Hydronic Systems Hydronic systems are the easiest to
zone as there is no possibility of coil freezing or high discharge
pressure. The only limitation occurs if you have
floor registers. If you have floor registers, you will need
to maintain enough air to keep the discharge temperature
below 140.F (60.C).
These systems do not have any limit to the number of
zones. Just be aware that reducing the airflow could create
noise in the remaining outlets due to overpressurization
of the plenum. If this occurs, use a spring
loaded bypass damper to recirculate some of the supply
air to the return duct.
It sounds as though you may benifit from investigating if a common chiller for all cooling needs' if your house is as large as the system design indicates you could reduce from 6 condensors to one or two chillers and not have long refrigerant lines.