High velocity questions - Page 2
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  1. #14
    Join Date
    Apr 2003
    Location
    the Great Pacific Northwest
    Posts
    607
    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?

  2. #15
    Join Date
    Mar 2005
    Posts
    37
    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

  3. #16
    Join Date
    Apr 2003
    Location
    the Great Pacific Northwest
    Posts
    607
    Humidification:
    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
    control required.
    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
    downstairs.
    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
    trip.
    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
    examples.
    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
    is 26.
    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.


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