Multi zone units and air conditioners

Dual-part system
In the two-track system, cooling and heating coils are embedded in two separate channels where the supplied air is placed in two parallel paths, one for heating and another for cooling. The advantages of parallel two ways are the ability to provide flexible satisfaction based on different required volumes and at different speeds as well as reverse temperature if needed.Dual-part system
The two-track system can integrate and mix hot and cold air in any region at all times.The two-way system can be either a two-channel/split system or it can be considered multizone system.These two systems have the same function in areas such as thermal dynamics, how temperature, pressure, air volume and mechanical performance are effective.The distinctive point of these systems is only in terms of the physical schema of the air integration site for each. region.

Design Notices
Possible Applications
Multi-zone air conditioners and multi-floor units can be configured and designed as heating, cooling and ventilation systems or ventilation and heating.Considering that the supply of heating floors was placed as a splinter of income in some cases that still needed heating system for those areas of heating coil, this progress was made from the top due to the economic dimension of this product.

The concept of using a divergence is that where space was ventilated solely by recursive mixed air and outer air, it led to the creation of a dead band between cooling and heating. One of the most innovative implementations of this concept is the use of conventional hot floors to provide neutral air from the dedicated outdoor air of the unit to the variable air volume boxes. Other types of use of this strategy include Texas multi zones.
*Variable air volume chambers variable air volume boxes

Cooling Coils
In line with the purpose of this discussion, we will mention cooling coils called “cold water coils”. Its purpose will be to investigate both “cold water coils” and direct expansion or DX expansion coils.*Variable air volume chambers variable air volume boxesCooling Coils
The use of DX coils in multi zone-multi-zone systems can cause complexities. The selection of coils, coil currents and condensers should be examined with functional systems to ensure the accuracy of the system’s performance. The risk potential of DX coils is considered in performance, but not the ratio of limitations including a little amount of cooling volume and compressor cycle and poor result in cold control and possible failures in the compressor.
A specific functional check should be carried out as long as a multizone system with DX cooling is in question.

Dual duct system specifications
The dual-channel system has the ability to inject and distribute air into the building through two separate channels during the constant and continuous flow of air. Hot and cold channels can be generalized to places occupied with temperature mixes to control the temperature settling in the conditional environment.Hot and cold air are brought to each region by separate channels.

Dual duct system specifications
– One of the most common cases in dual channel systems is the use of high pressure air distribution systems by reducing the pressure in mixing box in each region.
– In each region of this system, a controlling thermostat is considered.
The two-channel system is used in larger buildings where air transmission through the air conditioner by a separate channel is impractical, as used in the multizone system.
Dual duct system specifications
– One of the most common cases in dual channel systems is the use of high pressure air distribution systems by reducing the pressure in mixing box in each region.
– In each region of this system, a controlling thermostat is considered.
A simple schema of the dual-channel system is displayed in the diagram below.

Multizone Air Conditioner

Specifications of multi zone – multi-zone multi-zone system
Multizone system is different from dual-duct system.
The conventional multizone system is a system of continuous airflow that can provide room air changes and provide suitable temperature and humidity space with extreme accuracy.

A primary multizone unit includes the air supply blower section, the coil section and the air drainage principle.Other parts such as filters, mixing boxes, access and storage compartment with an air suction return blower are recommended for customized functional needs. Units and discharge units with multi-zone dampers or two-channel openings can be performed in any standing or horizontal configuration mode.

• Multizone systems use regional dampers placed in the air unit to combine warm air from heating coils and cold air from cold water coils to regulate the air temperature required by a space and region to the necessary and appropriate amount.
• Damper zone, proportional mixed air, mixed air flow in each area will be kept almost continuous.

• A regional thermostat controls everyft of the damper zone.
• Each region is designed to have a separate channel stretching all the way from the airsazetta to the desired space.
Multizone system is one of the best choices for offices, schools and other similar buildings that have a small space and require independent temperature control of their region.

Multizone Dampers
Multizone dampers are very low leakage dampers with vertical orientation and parallel damper blades. Each multizone damper consists of two dampers. One for the cooling floor and the other for the heating floor. Damper blades are aligned to a balanced limit of 90°C for hot and cold floors. Check photos of number 2.
Multizone Dampers
Therefore, an activator may act simultaneously in two hot and cold floors, as long as the damper opens one floor, closes the other floor, and on the contrary, each region needs a use of the activator, so calculating the torque for each region is separately considered as a requirement. However, each region may have its own width.

Check photos of number 2.
Multizone Dampers
Solutions multizone section:
A multi-zone part should be used to provide different air discharge currents for specific parts of the building.
• Each region receives two types of air discharge flow from multizone.
One of the airflows is considered “cold” and the other is considered “hot”.
• These airflows merge and mix before entering space.

• Multizone damper adjusts and controls the amount of cold and warm air flow that will be transferred to the environment according to the needs of that section, especially to cooling or heating.
• The part of the multizone that supplies cold air is known as the “Cold deck” and the part that supplies hot air is known as the “hot/hot deck floor”.
• The bottom row is cold deck, which includes diffuser or Plenum diffuser and cold water coil and a damper of the cold floor section.

1- When the DWDI fan immediately establishes the opposite airflow of the multizone, the multizone should use a /diffuser player as the first component in the lower row of the multizone.
2- As long as the airflow part of the multizone is not a DWDI fan, access to the Plenum plenum is considered as the first component in the multizone row.

– The upper row of heat floor includes a heating coil installed horizontally (in order to create vertical airflow) and hot floor dampers.
– The inlet air is divided into two airflows or plenum. One of the airflows that rotates upwards and passes through the heating floor and passes through the coil, exits from the back or top of the unit by passing through the hot floor dampers.

– The other airflow passes horizontally through the cold water coil and exits from the back or above the unit by passing through the cold floor dampers.
• Air pressure balance reduction plates are used to balance the pressure drop during hot and cold floor coils when needed.
When the DWDI fan is immediately located in the opposite air stream of the multizone, the configuration and placement of the fan should be such that the horizontal reverse imagination is done.

Multi-zone air conditioner

ANSI/ASHRAE/IESNA Restrictions
The increase in energy costs has limited the use of conventional multizone systems that consume more energy than single-channel systems as long as they need to supply cold and warm air simultaneously and integrate it to create the required airflow with the required temperature and humidity.

Also, controlling multizone system is more important to limit heating and cooling.
In addition, the best way to conserve energy in multizone reheating system is to minimize the integration of cold and warm air. You can reduce energy consumption by basically adjusting the temperature of the desired area or determining the temperature of the heating air and cold water coils.

Reset controls are also used to automatically supply air temperature to achieve optimum temperature, which in these methods is considered considerably low cost.

However, we should mention the limitations imposed by organizations such as ANSI/ASHRAE/IESNA in 2004 to multizone systems. Standard 9001 per section (6.5.2.1) states that the thermostat control system in each region should be such that it is possible to arrange the amount of heating and cooling of each section. Control systems should be such that cooling or reheating and merging and mixing simultaneously air that has already been mechanically heated or cooled, whether for mechanical or economical reasons.

Compliance Standard 9001
In order to implement the 2001-(6.5.2.1) 2004 multizone system contract, they must comply with one of the following standards.
1- Simultaneous cooling and heating is permitted when the airflow rate which is re-cold or hot or merged is minimized. And this rate is greater than the following:

.a Outdoor air volume required for ventilation in accordance with ASHRAE standard 6.1.3.
.b cfm /ft2 0.4 ground level conditional area.
.c 30% of the peak supply rate in the design area.
.d 300cfm to this standard is for sectors whose peak flow rate generally does not exceed 10% of the fan system flow rate.

.e Any higher rates observed, to reduce the overall annual energy consumption by neutralizing heating and re-cooling of wasted energy along the way, reducing the intake of inlet air in accordance with the required space according to ASHRAE 12 standard.
2- In sectors where the need for high pressure, especially mutual doping or minimum circulation rate code-required, different air volume systems become practically unusable.

3- Parts where at least 75% of the energy for reheating or providing hot air in the mixing part of the system is provided by site-recovered (which includes heat condenser) or solar site system.

Design Tips:
In the following, we will discuss some points that should be considered when designing a multizone system:
– Designers should use a main volume damper with reverse blades and against the manual direction near the unit in order to help create the aerial balance. The amount of air received in our desired location may vary depending on the static pressure fluctuations passing through the filters and conditions.

– In designs that include a considerable number of sections, it is better to keep the static pressure of the section channel as low as possible to the leakage boundary. The maximum leakage rate of the canal should be about 2% of the air injection rate. (According to SMACNA standard, leakage up to 10% is allowed).

– Measing or merging dampers should be periodically checked in terms of proper placement and operation, as they must provide the ability to prevent air merging and mixing when full cooling or heating is required in the sector.
– Selecting the dampers with minimal leakage is very important.
– Specify places with the same volume received for an area and do not mix interior spaces with outdoor spaces.

– Place the sensor or t- start in the section itself and determine that the part sensor is functioning properly to control the relevant part.

Advantages of multizone system:
Multizone units offer the following advantages:
– From the control point of view, multizone units are relatively simple and inexpensive and have a small error percentage. If you combine the sensors in the damper mixing actuator for each area and the heating and cooling valves, you will have a multizone control.
– The convenience of multizone system includes minimal need for high coverage, convenient installation capability and having control tools to integrate cold and hot airways located in the center of the air conditioner.

– Since the multizone fan acts as a system with low static pressure, it thus creates a relatively lower sound. Also, the fan is located in the middle position of this unit in order to minimize the fan output vibrations and coil or kissing failures. Removing the performance defects of the fan will be very related to the sounding problems of different aerial systems, because the fan works at a very low speed, hence it is classified as class I fans that create soft performance with high and long-term tolerance.
– Multizones will also be very durable systems that are limited only to subsidiary care and repairs.

Disadvantages of multizone
The disadvantages of multizone units are as follows:
– When there is a need for many separate channels, the number of sections should be limited.
– Also, in these systems, the amount of energy loss due to the existence of two floors of simultaneous cooling and heating to produce the required airflow of the conditional section and the re-temperature control of the hot floor is high compared to other systems.

– In these systems, it is very difficult to run an affordable cycle.
– Multizone system is generally customized and designed and a fixed range is specifically set to meet certain needs.

Segment sizing
The example ahead uses a multizone damper for a unit the size of @10,000 cfm. Each section consists of blades “6. The end of the sections for this particular damper will each have “8 widths. The internal sections of this section are “6 widths for the total “100”.

Note:
The end of each section includes a “6” blade and a fitted sheet for cabins of different sizes. (Photo No. 7) The total maximum cfm will be section 1000, which will be broadcast in 9 sections. Sections will require cfms ahead: 700; 1000 ; 2500 ; 1700 ; 500 ; 400 ; 400 ; 1000 ; 2000cfm

First, determine the amount of cfm per inch of damper length. 100cfm/in= 10000/100ʺ so cfm ideal for section 8″ will be equivalent to 800cfm and 600cfm for section 6″.

– The first part requires the equivalent of 700cfm, .cfm ideally the first blade will be 800. The first part is referred to the first blade. (First zone to the first blade ).
– The next part will require the equivalent of 1000cfm.The ideal total cfm of the next two blades will be 1200.The next part will be referred to the next two blades.
This process will continue until the completion of the second referral to the last section is fully determined. The specifications of the sections will be in accordance with the table below.

• The last area will require 1800cfm but the ideal cfm for the last blade available will only be 800.
The last area will require 20″ of the dampery with the related width. Therefore, two “damper 6” blades should be taken from the previous area and given to the last area.
Sections 1, 5,6,7 only each have one blade so smaller cannot be made. Sections 8,4,3,2 will have more than one blade.

Part 2 has an ideal cfm of 1200 and a real cfm of 1000 with a difference of 200cfm. If we reduce a blade it will have an ideal cfm of 600 and a real cfm of 1000 difference of 400cfm. The ratio of this difference to actual cfm is 400/1000 or 0.4.
We will have the same calculations for regions 8,4,3 by offering ratios of 0.4, 0.29, 0.28, respectively.

The 4,3 zone had the lowest ratio, so we can get a blade of 6″ from each area. However, if only one blade is removed from zones 3 or 4 in zone 9, we will have an ideal cfm of 1400 and a real cfm of 1800 with a difference of 400, which will have an impact of 0.22 ratio.

Note:
For more information, please refer to the source: Installation Guide for Air Conditioners Form 102-20-171.
The last segmentation order is as follows:

Contractor’s responsibilities:
In order to finally connect the channels of the sections to the damper zones, the person responsible must check the damper blades before installing them to ensure that all blades are detached at an angle of 90 degrees. Rotate the dampers to ensure that no interference occurs. All bars, shoulders and screws of dampers should be checked to ensure that each of them is firm. Also, it should be ensured that the correctness and safety of the connection of shaft kits and couplings in each damper should be ensured that the specific needs of each section of the connection and placement needs should be examined and considered in the design type. It should also be noted that in addition to the performance of the equipment, the person responsible should have thoroughly studied and understruded the full information about the types of equipment, connection, transportation and assembly and demontage methods.

” fundamentals of HVAC systems” chapter 9 & 10, Richard R. Johnson,Ph.D.ASHRAE society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

“Air Conditioning Design Mannual” chapter6, ASHRAE 581-RP Project Team, 1993 American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

ASHRAE.2004.ANSI/ASHRAE/IESNA standard 90.1-2004 Energy Standard for Buildings. Atlanta,GA; American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

ASHRAE 2004.ASHRAE standard 90.1. User Manual, chapter 6.Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers, In