Andrew Corney
Overview
This template generates a central DOAS air handling unit that provides a constant volume of conditioned outside air to all zones. It also generates an object in each zone that can provide heating and cooling, supplied by central chilled water and heating hot water plant.
Application
This system is used for five system options within Sefaira:
- Fan Coil Units (4-pipe)
- Active Chilled Beams
- Passive Chilled Beams
- Ventilation and Heating Only
- Radiant Floor
For each option the central AHU is virtually identical, with the exception of some defaults.
Changes were made to defaults and equipment at the zone level to achieve equivalents to the above systems.
Air Handling Unit (AHU) – Return Air
The table below describes the key properties of the AHU for this system where there is return air:
|
AHU Feature |
Default |
Extent of user-control |
|
Airflow Rate |
Based on ventilation rate by zone |
Can change zone ventilation rate or set a fixed constant primary air flow rate |
|
Supply Air dry bulb Temperature |
Constant with defaults as follows: 13 C or 55.4 F (Fan Coil) 11C or 51.8F (Active beams) 14C or 57.2F (Passive beams) |
Can change constant value |
|
Supply Air Temperature Reset Controls |
None |
No control |
|
Supply Air Dew Point Controls |
Constant with defaults as follows: Min: -5 C or 23 F Max: 13 C or 55.4 F (Fan Coil) Max: 11 C or 51.8 F (Active Beam) Max: 10 C or 50 F (Passive Beam) |
None |
|
Supply Air Humidification Controls |
Via Min Supply Air Dew Point Control |
None |
|
Peak Fan Power |
3.5 W/(L/s) or 1.65 W/cfm |
Can control peak load |
|
Fan Curve |
Standard ASHRAE. Click to see fan curve. Note airflow is not variable |
No control |
|
Outside air configuration |
100% outside air |
No control |
|
Return Air Rate |
100% of air assumed to be returned for heat recovery |
No control |
|
Heat Recovery Efficiency |
Sensible and Latent effectiveness available. Default is 50% sensible and 0% Latent. |
User can change sensible and latent effectiveness |
|
Cooling Coil |
Chilled Water coil post heat recovery |
No |
|
Heating Coil |
Hot water coil post chilled water coil |
Can change to electric coil or direct gas |
|
Frost Coil |
Electric coil pre-heat recovery |
Can change to hot water |
|
Frost Coil Setpoint |
Setpoint for coil – default is 2C |
Can Change default |
Zone Fan Coil Units
Fan Coil Units are the basic system applied to the following options:
- Fan Coil Units (4-pipe)
- Active Chilled Beams
- Passive Chilled Beams
- Ventilation and Heating Only
In other words – for all of the above systems it is assumed that heat transfer by the zone heating and cooling unit is purely convective. For the above systems the only variables that are changed are defaults.
The table below describes the key properties of the zone level Fan Coil Units for this system:
|
Fan Coil Unit Feature |
Default |
Extent of user-control |
|
Heating Coil Type |
Hot water |
No control |
|
Cooling Coil Type |
Chilled Water |
No control |
|
Fan Coil Motor Type |
Constant Volume (On/Off) except for Chilled Beam Systems that has none |
No control |
|
Peak Fan Power |
0.64 W/(L/s) or 0.3 W/cfm |
Can control peak load |
|
Fan Curve |
Constant Volume Fan |
No control |
|
Supply Air Temperature - Heating |
Variable for Fan Coils and Heating Only. Constant for all zones (35C / 95F) |
User can change constant |
|
Supply Air Temperature - Cooling |
Variable for Fan Coils and Heating Only. Constant for all zones (13C/55.4F) |
User can change constant |
|
Demand Control Ventilation |
None |
None |
|
Dehumidification Load |
All systems will dehumidify to achieve the cooling setpoint at 60% Relative Humidity in the zone |
None |
Radiant Floor
A radiant floor element replaces the fan coil units for the radiant panel option
The table below describes the key properties of the zone level Fan Coil Units for this system:
|
Fan Coil Unit Feature |
Default |
Extent of user-control |
|
Heating Coil Type |
Hot water |
Can change to electric coil |
|
Cooling Coil Type |
Chilled Water |
No control |
|
Temperature Control Method |
Operative Temperature. Note this means that the setpoints in internal conditions become operative temperature setpoints |
User can change to dry bulb or radiant temperature. |
|
Surfaces conditioned |
Floor only |
No Control |
Central Plant
The base case option is assumed to have a central plant that provides heating hot water to the AHU and Fan Coil Units and a chilled water system that provides chilled water to the central AHU. The only exception is the heating plus ventilation system which does not include a cooling plant.
|
Central Plant Feature |
Default |
Extent of user-control |
|
Heating Hot Water Source |
Natural Gas |
Can change to electric boiler |
|
Boiler Peak Efficiency |
Assumed to be 0.9 |
Value can be changed |
|
Boiler Performance Curve |
No Control |
|
|
Supply and Return Temperatures – hot water |
80/70 C or 176/158 F |
User can control |
|
System losses |
Constant efficiency of 15% |
User can control loss rate only. |
|
Peak Pumping Energy |
1.32 W/(L/s) or 21 W/gpm |
No control |
|
Pump Efficiency Controls |
Variable Speed Drives |
No control |
|
Efficiency Curve for Variable Pumping |
No control |
|
|
Pumping Configuration |
Primary Only |
No control |
|
Chilled Water Source |
Water-cooled Chiller |
Can change to air-cooled |
|
Chiller Peak Load Efficiency |
5 |
Value can be changed |
|
Chiller Performance Curve |
No Control |
|
|
Supply and Return Temperatures – chilled water |
7/12 C or 44.6/53.6 F |
User can control |
|
System losses |
Constant efficiency of 10% |
User can control loss rate only. |
|
Peak Pumping Energy |
1.32 W/(L/s) or 21 W/gpm |
No control |
|
Pump Efficiency Controls |
Variable Speed Drives |
No control |
|
Efficiency Curve for Variable Pumping |
No control |
|
|
Pumping Configuration |
Primary Only |
No control |
|
Separate chilled water loop for fan coils |
None |
None |
|
Waterside Economiser |
None |
None |
|
Condenser Water Source |
Cooling Tower |
No extra options |
|
Cooling Tower Efficiency |
245.7 W/(L/s) or 15.5 W/gpm |
Value can be changed |
|
Supply and Return Temperatures – condenser water |
29/35 C or 84.2/95 F |
User can control |
|
System losses |
Constant efficiency at 5% |
User can control loss rate only. |
Post Expansion notes about Fan Coil Units
There are a large number of objects that are modified post-expansion which can result in inconsistencies between some outputs in the standard E+ reports and the Sefaira outputs.
- Impact of Ventilation Air on space load
- Heat Recovery in the central air handling unit
- Insertion of radiant heating in lieu of fan coil units
Please explain me please explain in more detail your comment regarding the Post expansion nodes about Fan Coil I. E. Insertion of radiant heating in lieu of fan coil units