VRF with DOAS Flashcards
What are the two main options for a VRF System?
Heat Pump VRF and Heat Recovery VRF
What is Heat Pump VRF?
All zones are in heating or cooling at once (majority rule)
Where is Heat Pump VRF applicable?
Large single zones, electrical rooms, etc.
What is Heat Recovery VRF?
Heating or cooling is determined at zone level. (energy RECOVERED between zones)
Where is Heat Recovery applicable?
Hotels, offices, condos, etc.
What are 3 key components for a VRF system?
Condensing unit, ducted fan coil and branch selector(HR VRF)
How does the FC modulate?
It looks at RA temp vs zone set point and uses an electronic expansion valve to regulate refrigerant flow
How does the CU modulate?
With variable speed compressors
What are branch selectors and when are they used?
They separate hot gas, cold gas, and liquid phases and direct flow of refrigerant to FCs. They are only used in Heat Recovery systems?
Thermal Expansion temperature difference in cooling and heating?
Roughly 40-50 in cooling and 170-190 in heating
What are the two pipes in a 2-pipe sytem?
High pressure liquid, low pressure gas
What is the added pipe in a 3 pipe system?
A high pressure gas
What are 3 expansion compensation strategies?
L bend, Z bend or pipe loop
2 things to remember about expansion loops
They should lay flat and be constructed with pipe and elbows, not flex joints
Hard pipe between ___ and ____
CU to BC
Line sets between ___ and ___
BC to FC
Single CUs generally don’t exceed ___ T
18
______ is the process of connecting more than one CU in a single system
Twinning
Common to see up to ___ CUs twinned together
3
Total system tonnage varies by manufacturer, but is typically
50
Where are isolation valve(s) located if branch selector is multiport?
Downstream of BC to allow system to stay operational if one zone has a leak, or if construction is phased.
Where are isolation valve(s) located if it is 1:1?
Upstream of branch selector to allow for service of BC or FC in this arrangement.
_____ ceiling units can have filter
installed at rear of unit
Unducted
_____ ceiling units should add the
optional factory filter box
Ducted
Pipe junctions should always use factory “_____” or Headers
Y Splitters
CUs become ____ in heating mode. If installed indoors they will need _____.
Evaporators, drip pan and condensate pipe to drain
Some branch controllers require condensate. _____ requires this. Check IOM
Mitsubishi
