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2016-05-13 02:41:57 -0500 | answered a question | GenOpt 3-1-1 installation problem Had the same issue recently. In section 10.2 (p. 75) of the GenOpt Manual it is recommended to install it in a different folder, one for which you already have read/write permissions. That would be any folder within your "User" folder, for instance your Documents folder. Then you can just copy the installed GenOpt folder back to "Program Files". Another (better) way though would be to open an elevated command prompt and run the installation script as Administrator. You can achieve that by typing |
2016-04-27 07:24:15 -0500 | commented answer | Baseline system parameters with DES heating in LEED? Yes, exactly, because when modeling District heating systems, the heating conversion efficiency is already taken into account in the purchased energy rate. So you end up having to model a "virtual" on-site boiler with 100% efficiency, which is equivalent to having no boiler and getting all of your heating energy from the DH network. By the way, if you are happy with my answer, please mark it as correct. Thanks, and glad to help! |
2016-04-26 09:03:38 -0500 | commented answer | Baseline system parameters with DES heating in LEED? Also, bear in mind that choices of supply and reset temperatures for hot water loop won't have a significant impact on the results (I checked one of my projects using DH and observed less than 1% difference). However, the pump specific power for the baseline will indeed have a significant impact. Which is why I usually stick to the baseline power limit specified in G3.1.3.5 in all situations. |
2016-04-26 08:58:46 -0500 | commented answer | Baseline system parameters with DES heating in LEED? Ok, now I see what can be confusing, thanks for pointing it out. I checked the 1.4 spreadsheet, and it's not clear whether this might be an error or not. And since the only clear indication is Section 2.4.1.1 of DES v2 Guidance which states that "Any system parameters not specifically referenced in Table 3 are modeled as specified in Appendix G", I would follow this and model the hot water loop according to sections G3.1.3.3 through 3.1.3.5 of ASHRAE 90.1-2007 App. G. |
2016-04-22 10:37:15 -0500 | answered a question | Baseline system parameters with DES heating in LEED? When going for DES v2 Option 1, you need to model both the Proposed and Baseline buildings' energy sources as purchased energy, as explained in section 2.4.1.1 of the DES v2 Guidance. The usual way to implement this option is to model a constant efficiency boiler with 100% efficiency on the hot water loop, and then apply a purchased heat energy rate to the estimated boiler energy. The exact implementation will differ depending on which modeling tool you use. Note that if your Baseline building uses the baseline system type 3, you will have to modify it according to Table 3 (page 11) of the DES v2 Guidance to make it compatible with a hot water loop. Now, with regards to the actual hot water loop parameters, Baseline supply temperature, temperature reset and pump power should be based on actual Hot Water loop conditions in the Proposed Case. I can't find this exact reference in the DES v2 Guidance document, but these are the instructions written in the Revised Section 1.4 spreadsheet. Also, keep in mind that when going for DES v2 Option 1 you have to calculate your purchased energy rate as outlined in section 2.4.2.1 of the DES v2 Guidance, under "District Hot Water Rate". Use these rates, which consider some default efficiencies for the District Heating plant, instead of those provided by your District Heating provider. Finally, be aware that you can only claim a maximum of 12 EAc1 credit points when selecting this option with LEED CS v2009, as per Table 1 of the same document. |
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2016-02-02 02:54:38 -0500 | answered a question | Estimate Fan pressure rise from ESP Once you have an idea of the ventilation system component layout, you can definitely estimate the AHU's Internal Static Pressure (ISP) using rule-of-thumb values, and from there estimate the Total Static Pressure (TSP = ISP + ESP). I've discovered that a good reference for typical pressure drops (in SI units) can be found in section 5 of AIVC Technical Note 65 - Recommendations on Specific Fan Power and Fan System Efficiency. Table 5 on page 23 gives rule-of-thumb component pressure drops for different design considerations (poor, typical or good design). According to these numbers, AHU's internal static pressure can be anywhere between 250 Pa (1" w.c.) for a good design and 650 Pa (2.6" w.c.) for a poor design, given a typical Filter+HX+HCoil+CCoil component layout. The External Static Pressure is usually between 400 Pa / 1.6" w.c. (for residential or smaller commercial buildings) and 750 Pa / 3" w.c. (for larger comercial buildings). The Total Static Pressure can therefore be anywhere between 650 Pa / 2.6" w.c. and 1400 Pa / 5.6" w.c. depending on the design assumptions and building size, and this obviously has a great impact on the fan energy use. Also, the TSP will be a bit different between supply and return (usually lower on return). This is important for EnergyPlus models but also for IES VE (when using ApacheHVAC) and eQuest models which also rely on Total Static Pressure to estimate fan system efficiency. |
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2015-09-29 09:54:58 -0500 | answered a question | Difference of n50 and infiltration rate It looks like by infiltration rate you actually mean the annual average infiltration rate, that is the air exchange under natural conditions. The given value (0.11 ACH) seems coherent with this assumption and it appears to be what you used in your energy model. As pointed out by @aparker, the n50 or ACH50 is the measure of the air exchange through the building envelope under a 50Pa pressure difference. Under natural conditions, the pressure difference will be much lower and varying depending on the building exposure and wind velocities and directions. However, a reference pressure of 4 Pa is typically used in the US to represent natural conditions (more details about that in this paper written in 1980 by M. Sherman and D. Grimsrud). If ACH50 is the air exchange at 50 Pa, we can say that the air exchange under natural conditions is ACH4 = 0.11 ACH at 4 Pa. In order to convert ACH4 to ACH50 some assumptions need to be made, and the air exchange rate should be converted to air flow rate first. Let's assume a building with an enclosed air volume of 10,000 m3. The air flow through the building envelope at 4 Pa would be: For a particular building, the relation between pressure difference and air flow through the envelope is linear, and the power law equation of flow through an orifice can be used to estimate the air flow at different pressures. Still, we need to make an assumption on the pressure exponent n which is unknown unless a blower door test was performed. This parameters represents the characteristic shape of the orifice and ranges from 0.5 (perfect orifice) to 1.0 (very long and thin crack). For a fairly air-tight envelope the exponent value would be around 0.6 or 0.7 and for a very good, air-tight envelope around 0.8 or even above. Let's assume n = 0.75 in the present case because this looks like a reasonably good, air-tight envelope. Using the power law equation we can determine the air leakage coefficient C given the air flow under natural conditions (4 Pa). Knowing the air leakage coefficient and pressure exponent, the air flow at 50 Pa can be estimated using the same equation: The previous two equations can be merged and Q50 can be obtained directly from Q4, without the intermediate step to calculate C: And because we know the enclosed air volume of the building, we can convert the air flow back to an air exchange rate: Fortunately, we can simplify all this by using substitutions and obtain ACH50 ... (more) |
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