HVAC System Design for Hazelwood Office Building

HVAC System Design for Hazelwood Office Building Introduction: The HVAC system design proposal includes 3 parts, the first one is the assumptions made to analyze, basically are the assumptions made for energy simulation. After obtaining the loads for design, the second part is the system chosen and design, which include the system introduction, product chosen as well as the installation. The third part is the assessment of the proposal. Assumptions: In general the Hazelwood office building is assumed to be a standard office building converted from an abandoned traditional 3-floor residential building. The assumptions to build up the IES model are listed as follows: Item Assumptions Source Occupancy 12 people in the building ( 250ft2/person) The ASHRAE 62.1 requirement is 5 people per 100m2 which is about 220ft2/person Schedule Lighting & Occupancy & Equipment: Weekdays: from 9 to 17 Weekends: from 9 to 12 Envelope Roof(R-38) Cool roof rated white TPO membrane Dark colored Elastic coat Polyisocynurate (R-19) Roof framing 3 cc SRF(R-19) Gypsum board External Wall East(R=24): Brickwork(9 inch) Insulation Board(1 inch) Expanded polystyrene(4inch) West(R=24.5): Paper Board(1inch) Insulation (4inch) Expanded polystyrene (2inch) North(R=26.3): Brickwork(4inch) Paper Board(1inch) Insulation board(4 inch) Expanded polystyrene (2 inch) South(R=24.5): Paper board (1 inch) 1 DOE Reference Building LECC 2009 LECC 2009

Insulation Board(4inch) Expanded polystyrene(2inch) Floor(R-30) 2*12 Frame with cavity insulation(r- LECC 2009 30) On the top of the cavity insulation, there is a layer of wood planks(1/4 inch) Basement Wall(R-12) Stone(4inch) LECC 2009 THERMALITE TURBO (3INCH) Basement Floor 0.5inch concrete+r-2.6 insulation LECC 2009 Glazing Company: Comfort Line Fiber Frame LECC 2009 8000 series Double Hung Double Glazed U-factor = 0.29 SHGC = 0.27 VT = 0.66 Air Leakage Rate 8 ACH@ 50 pa The LECC 2009 requirement is 7 ACH@ 50 pa but generally the building could not reach that level Lighting Manufacturer: CREE LECC 2009 CS18 for the main space and front space LR6-18L for the staircase The calculated LPD is 0.436W/ft2 Equipment equipment power density are assumed to be LECC 2009 0.5 W/ft2 2

System Design: The process for the system design is first to get the design load from the IES software. Then decide the system type to use and look for the suitable product. The energy simulation results will be used to see the performance. Last is the installation of the whole system to make it more feasible. 1. Design Loads Ground Floor First Floor Second Floor Peak Load Design Load Heating Cooling Heating Cooling 31742 12516 3Ton 1.5Ton 18692 8494 2 Ton 1Ton 20473 11998 2 Ton 1Ton So after the simulation, the peak load for each zone is calculated by IES. The total design load for each floor is obtained. It is found that the ground floor has the highest heating and cooling load. This is probably because the roof insulation on the top floor is much better than the wall insulation and meanwhile the ceiling height of the ground floor is much higher than the other two floors. The second floor has the lowest load due to its smallest exposure area. 3

2. System Chosen After obtaining the loads, it is time to choose the system. We have been considering the GSHP, ASHP, mini-split systems as well as the packaged HP with furnace and finally choose the last one. The main reason is that although the GSHP is the most sustainable one in long term, it is expensive initially and relatively harder to maintain. Although the ASHP is affordable, it won t be effective in extreme cold conditions. The mini-split systems failed to deliver the supply air in comfortable temperature unless one installed on each conditioned zone which is however too expensive. The biggest advantage of the packaged HP&Furnace system is that it does not have those issues and on the contrary cost effective, energy efficient, friendly to the user. The detail assessment will be discussed in the last part of this report. It also should be noted that for the initial proposal, the furnace is electric furnace which could get rid of the gas piping and metering and thus easier to build and maintain. As for the DHW system, there is no significant demand of domestic hot water in the small office building. According to the energy analysis later, it could be found that the annual energy consumption on the DHW is less than 1% of the total energy consumption. A small electric boiler in the basement could be useful because in this way there is actually no need of natural gas in the office building anymore. Also, some point of use electric water heater could also be considered, which reduces the energy waste from delivery. Next is to find the proper products. Actually the packaged system could be either prefabricated or assembled later by the user. There are some prefabricated products and some manufacturers are good at it like Carrier, Bryant. Here is a product link of the Carrier s hybrid system which is of packaged heat pump and gas furnace. (http://www.carrier.com/homecomfort/en/us/products/heating-andcooling/packaged-product/product---packaged-products---48xt/) However, since these systems are all gas furnace, the Heat pump and electric furnace has to be found separately. The heat pump power should meet the cooling load demand and the electric furnace should be able to cover the heating need. 3. Products chosen The final chosen system are listed as below: Heat Pump The heat pump found is an energy star certified heat pump with 1 and half ton of both heating and cooling capacity. The detail specification is pasted below. Its SEER rating is very high and therefore very efficient. Furthermore, all floors could use this Heat pump because it meets the cooling demand on each floor. 4

Electric Furnace The electric furnace is not usually used compared to the gas furnace. 2 possible choices that could be used here are presented below. First one is 3.5 ton for ground floor and the detail is shown below. (http://mobilehomepartsstore.com/merchant2/merchant.mvc?screen=prod&product_code=360601) Another reason to choose this one is because this one has a built-in cabinet which could easily install the heat pump inside 5

The second one is Winchester 32,765 BTU 2 Ton Multi-Positional Electric Furnace. It could be used for the first floor and second floor which have relatively lower load. (http://www.homedepot.com/p/winchester-32-765-btu-2-ton-multi-positional-electric-furnace- WMA24-10/202771104#) This system has average performance and it is hopefully to get upgraded by the manufacturer. The cost is %649 each. 4. System Installation The schematic diagram of the proposed systems is presented as below: (Packaged HP and electric furnace): The left cooling coil and heating coil are from the heat pump and the heating coil on the right side is the electric furnace 6

There are lots of controllers basically used to make the furnace work in winter while heat pump work in the rest of time of a year, which is not extremely cold. Each floor has one set of the system and duct work, including supply, return and exhaust The heat recovery device in the chart is not activated, but it is possible to activate it. The detail system component placement and installation in the building is presented as below: 7

This diagram shows how the ducts connected in the building. There are two ducts out of the package unit to supply and return the air. There is one input duct with mixed fresh air and return air. Two pipes of the unit connect to the condenser on the top of the building. The supply grill must be far away from the return grill to help air circulation inside. The fresh air is from a hole cut on the same floor but wellsealed to ensure air tightness. The exhaust duct is from the restroom and possible to exchange heat with the fresh air. 5. Energy Simulation Result: With all the retrofit strategies, the IES is used to run the simulation and detect the energy performance. In order to have a comparison, the before-retrofit HVAC system is standard DX and furnace system recommended by ASHRAE 90.1 2007 and sized for the building which should be much better than the existing HVAC systems. The site to source energy conversion factor used here are electricity: 3.363, gas: 1.092 from national average in Building America House Simulation Protocols. Before Retrofit 8

After Retrofit Energy Saving: Energy Savings include both site energy and source energy and the main concern is the heating, cooling as well as total energy. Site Energy: 30% 20% 10% 0% -10% -20% -30% -40% -50% -60% -70% Site Energy Saving after HVAC Retrofit 18% Heating Cooling Total -33% -63% Heating Cooling Total 9

Source Energy: Source Energy Saving after HVAC Retrofit 25% 23% 20% 18% 15% 10% 13% Heating Cooling Total 5% 0% Heating Cooling Total The site energy of the proposed HVAC system is pretty low due to its application of electricity which is much more efficient in terms of site energy. With consideration of the conversion factor, the electricity is 3.365 while the natural gas is only 1.092, the source energy is increasing. It should also be noticed that there are some assumptions made to run the simulation, like when to use the heat pump when to use the electric furnace. In the modelling, the furnace will be used from December to February and the heat pump be used for the rest of time. But furnace may not be necessary to be used for the whole winter. The electric furnace is less efficient compared with the Heat pump, therefore the more use heat pump, the more energy saved. Based on this result, a further step is taken to detect the energy performance. As I introduce before, the energy simulation with heat recovery has been tried. An ERV system with average performance (70% sensible heat recovery, 70% latent heat recovery, 0.15kW) is added to compare the energy performance. 10

Additional ERV system: Site and Source Energy saving compared to the proposal: 6.00% 4.00% Source Energy Reduction after HVAC Retrofit 3.63% 2.00% 0.00% -2.00% -4.00% -6.00% -8.00% -10.00% -12.00% Heating Cooling Total -9.85% -4.28% Heatin g Coolin g 11

The result shows that both the heating and cooling energy consumption have been reduced while there is extra energy consumption running the ERV system that on the contrary causes the total energy consumption increased. This result is also reasonable because the heating energy consumption has been reduced by almost 10%, cooling by 4.3% and they are within the reasonable range. The difference with that expected is the power consumed by the ERV is more than the benefit caused by the heat recovery. It is probably resulted from the relatively complicated system that requires a higher head pressure to run the ERV. However, as mentioned before, the result is based on several assumptions. If the ERV system is more efficient, the energy performance might be different. But meanwhile it reflects that the heat recovery system may not be performing as well as we expected in the Hazelwood office building. Furthermore, it actually could be predicted using the natural gas furnace will definitely have a better performance in terms of source energy if not for the convenience of metering and to avoid extra work of gas piping. This is because the electricity conversion factor is too high; the electric furnace is not very efficient with consideration of the conversion factor while the natural gas furnace is more efficient. Therefore, another study on the gas furnace is taken and the result proves the predication. Energy Performance Using Gas Furnace 12

Site Energy compared with the baseline HVAC: 30.0% 20.0% Site Energy Saving of Packaged HP & Gas Furnace 18.3% 10.0% 0.0% -10.0% -20.0% -30.0% -40.0% -50.0% -60.0% Heating Cooling Total -55.6% -28.2% Heating Cooling Total Source Energy Compared with Baseline HVAC: 30.0% 20.0% 10.0% 0.0% -10.0% -20.0% -30.0% -40.0% -50.0% Source Energy Reduction of Packaged HP & Gas Furnace 18.3% 1.3% Heating Cooling Total -40.4% Heating Cooling Total The result proves that the source energy performance of the gas furnace is much better than the proposed with electric furnace. However, it is surprising that the source energy consumption of the system is still a little higher than the baseline performance. The increase mainly occurs in the increase in the system electricity, like fans, pumps as well as cooling. Probably this is because the complexity the systems are, the more head pressure in the system. As a result, the power to deliver the air is raised. 13

From the studies above, it could be simply concluded that the packaged Heat pump and gas furnace, is generally in the similar level of performance as the baseline HVAC system in terms of source energy performance. But the site energy could be saved significantly. System Assessment Based on all the study above, a conclusive analysis about the proposed system could be conducted using triple bottom line. The triple bottom line includes the planet, people and profit. Planet: As for the planet, the main two concerns are the energy and environmental impact. In theory, the proposed packaged heat pump and electric furnace system is energy efficient. This combination of use is better than the packaged A/C and furnace. Heat pump could be used for moderate heating conditions and all the cooling demands. The electric furnace will be switched on when the outside temperature is significantly dropped. This way ensures the efficiency of both systems and thus makes the system energy efficient. The result shows that the site energy saving is indeed tremendous while source energy consumption is actually increased. As discussed before, this is because the electric furnace is not too efficient if with consideration of the source to site energy conversion factor. However, it should be known that the baseline HVAC system is already a standard system that meet ASHRAE standard and are actually above the existing level of Hazelwood Office HAVC system performance. Meanwhile, it is also recommended to use gas furnace instead of electric furnace because the gas furnace will be more energy efficient in terms of source energy. The impact on the environment here could be analyzed based on the Carbon emission amount. The results are generated from the IES software: Total Carbon Emission (lbco2) Baseline (DX+Gas Furnace) Packaged Heat Packaged Heat Pump Pump & electric & electric Furnace Furnace +ERV 36998 13859 17137 13859 Packaged Heat Pump & Gas Furnace It shows that both the packaged Heat pump with electric furnace or gas furnace performs the best and is much better than the baseline HVAC system. 14

Another concern for the environmental impact is the refrigerant. The system I have chosen is using R410 in the heat pump, which is very friendly to the Environment. Meanwhile, it is very normal today. Therefore, the proposed systems with either electric furnace or gas furnace are the environment friendly choices. Profit: As for the profit, the main concern is the economic feasibility for the project. According to another case study for housing retrofit in MA which is 1400 SF that about 1/3 of our size, the proposal is a completely feasible one within budget. (Single-Family House BEDFORD) It uses 14 SEER split system for cooling and 95% AFUE gas furnace for heating. In this case, the total cost for electrical, pluming, mechanical equipment as well as installation is only about $21/SF, which is attractive. Further, the initial cost for the electric furnace is even lower than the gas furnace and the normal life span of electric furnace is higher than the gas furnace. Because there is no gas piping and gas metering, the initial cost is possible to be even lower. Therefore, the proposed system with either electric furnace or gas furnace as well as the related pluming should be totally affordable and the electric ones are even more economically feasible. So, if the proposed systems could be applied, lots of investment could be saved and used to improve the design of other parts, especially the envelope. However, the proposed system does not save operating cost compared with the baseline HVAC system because actually the operating cost is in line with the source energy performance. But the difference is quite small. People: The big advantage of the proposed system is the easy maintaining. Compared with VRF, GSHP, this system is easy to understand and maintain even without technician. Furthermore, if electric furnace is used, there is no gas piping and therefore the house is safer without the concern of the leakage. In conclusion, the recommended system could be different based on the owner preference. if the priority is the source energy saving, long term financial saving, a packaged heat pump and gas furnace system is recommended, actually a well-performed DX +furnace system is also recommended. If the priority is the site energy saving, environmental impact, initial cost and as well as the easy maintaining for the user, the initial proposal with electric furnace is recommended. In addition, the ERV system may not perform as well as we expected and therefore it is not necessary a choice to further improve energy performance. 15

Reference: 1. Carrier Hybrid Heat System http://www.carrier.com/homecomfort/en/us/products/heatingand-cooling/packaged-product/product---packaged-products---48xt/) 2. Electric Furnace 1 (http://mobilehomepartsstore.com/merchant2/merchant.mvc?screen=prod&product_code=3 60601) 3. Electric Furnace 2 http://www.homedepot.com/p/winchester-32-765-btu-2-ton-multi-positional-electric- Furnace-WMA24-10/202771104#) 4. Source to Site ratio http://beopt.nrel.gov/sites/beopt.nrel.gov/files/help/electricity%20source_site%20ratio.htm 5. Single Family House BEDFORD, MA http://www.buildingscienceconsulting.com/presentations/documents/02-bedford_single.pdf 16