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Good points. I guess implicit in your reply is that both designs are acceptable in some cases.

1/ No branch is more than 1,5m in length
2/ There is only one main trunk, everything will be made...

This particular board is coated with aluminium on the outside and a noise absorbing cloth on the inside. Pressure loss graphs are near identical to the ASHRAE ones for a galvanized tube and so the...

I have two designs for the same airduct to be made from glass fibre duct board. The distribution duct passes by two rooms which both need cooling and one design has two single branches (like off...

Hi yes I not from the US, was it the ductboard or the metric units?!!

Isover states a max speed of 18m/s (3500 PFM) at 90°C and suggests an optimum flow of 8m/s (1500PFM) in its literature. As you...

I have seen various speeds quoted in the forum and on the web for air flow velocities. Most sources dont quote material and I dont know if that is becuase the material does not matter (something I...

by "Reach" I mean the distance travelled by the air leaving the grille, normally taken as the distance at which the velocity has fallen to <= 0,5 m/s
The faster the air leaves the grille, the...

2CFM per square inch = 0,5 m3/h per 1cm2. That is slightly oversizing the grills, there seems to be some difference between manufactures of double-defection impulsion grilles. Some makes required...

I read that impulsion grille size has an impact on (turbulence) noise and note that the target noise level seems to be 30-35 dBA in homes. If the duct behind the grille is correctly sized to maintain...

I would appreciate opinions from members on whether or not it is worthwhile controlling the return airflow in a zoned system.

We plan to install a system of motorized rectangular grills located in...

I would appreciate comments on whether or not the new SEER rating (EU directive 626/2011) is a good indicator for efficiency in warmer climates. It is interesting to note that for heating they have...

VRV systems are clearly very different in terms of input power usage.

The daikin split concealed unit databooks suggest that the most efficient "seasonal units" have input power coefficients of...

I would love to know where you get ERR breakdowns by load. This data is not released normally in Europe, or at least Mitsubishi, LG and Fujitsu dont give it.

I believe SEER is based on constant...

First thanks for such a detailed reply.

A water based system is not an option as this is an old building with ceramic walls and marble floors but more smaller air units is. The issue is will...

Thank you for your comments. Efficiency in an actual application is difficult to define and measure but I believe in a lab with a set airflow and defined humidity and internal and external...

The 1kW min load is a night-time scenario and so the units would need to meet this 8hrs*7 nights or 35% the time.

The concern about cycling is not only higher power consumption but also the...

I spoke with Daikin and Mitsubishi. The Daikin units get to 50% of nominal before stopping. They are inverters but as with any motor, cycling consumes more power than running continuously. If their...

principally is the dynamic range. Can you identify HVAC that can work at 10% (ie cool at 10kW or 1kW)? Most seem to reach 50% at best.

We presently have a similar configuration: outdoor unit (10kW) and concealed internal unit with a fibreglass duct for distribution. There is a gas central heating system so the units are only used...

MEE: PUHZ-ZRP-VHA/ PEAD-RP-JAQ
http://www.mitsubishi-aircon.co.uk/mitsubishi_electric.asp?id=191236...

I can its not easy but if there a standard for the "nominal" numbers surely they could quote min compressor numbers using that?

Or measure power consumption versus cool air production?

We are looking to install 2-3 ceiling concealed units in a large house. The key problem we have is dynamic range: the cooling/heating requirement can be a low as 1kW and as high as 10kW.

We are...

the duct manufacturer passed me another spreadsheet to cross-check sizing with their specific material and this assumes airflow at the internal unit as 5-6m/s (1230-1476 fpm) and is reducing the duct...

thank you, that is 500 byt/hr sensible. 150W per appliance gives a much lower number.. Curiously that is what I was estimating for a PC with monitor.

I would like to check some figures I have been given for cooling loads.

I can see the loads from external sources but was wonder if 2kW of additional cooling is necessary for the electric oven,...

Thanks for the reference figures, which in SI are:
900 fpm= 4,6 m/s
700 fpm= 3,6 m/s
500 fpm= 2,5 m/s

I guess these figures are the limits to avoid noise? Should the design slow airflow in the...

Hi there, here are US units in decimal (sorry dont know how to make EXCEL format ft/inch). The CFM values are shown in the original post:



Section
Load (kW)
CFM
Actual width (feet)
Actual...

I would appreciate some help evaluating a proposal for renovating an existing central air conditioning system.

The new units provide 3 airflow rates of 17-21-25 m3/min (618-742-883 CFM) and...